Chapter XV

(the most elaborate mechanism included in the book) with

very simple tools. Some of the items which I had on my original list were abandoned, because they presupposed the possession of comparatively expensive machines.

My selection has also been guided by the desire to cater for different tastes. In some cases the actual manufacture of the thing described may be regarded as the most instructive and valuable element, and may appeal most forcibly to the “handy” boy; in others—the Harmonograph provides a good instance—the interest centres round the experiments made possible by the construction of a simple piece of apparatus; in some the utility of the article manufactured is its chief recommendation.

I feel certain that anyone who follows out the pages of this volume with hand as well as with eye, will have little reason to regret the time so spent. The things made may in course of time be put aside and forgotten, but the manual skill acquired will remain. Nowadays one can buy almost anything ready-made, or get it made without difficulty; yet he who is able to make things for himself will always have an advantage over the person to whom the use of tools is an unprobed mystery.

Contents

I. SAWING TRESTLE II. A JOINER’S BENCH III. A HANDY BOOKSTAND IV. A HOUSE LADDER V. A DEVELOPING SINK VI. A POULTRY HOUSE AND RUN VII. A SHED FOR YOUR BICYCLE VIII. A TARGET APPARATUS FOR RIFLE SHOOTING IX. CABINET-MAKING X. TELEGRAPHIC APPARATUS XI. A RECIPROCATING ELECTRIC MOTOR XII. AN ELECTRIC ALARM CLOCK XIII. A MODEL ELECTRIC RAILWAY XIV. A SIMPLE RECIPROCATING ENGINE XV. A HORIZONTAL SLIDE-VALVE ENGINE XVI. MODEL STEAM TURBINES XVII. STEAM TOPS XVIII. MODEL BOILERS XIX. QUICK-BOILING KETTLES XX. A HOT-AIR ENGINE XXI. A WATER MOTOR XXII. MODEL PUMPS XXIII. KITES XXIV. PAPER GLIDERS XXV. A SELF-LAUNCHING MODEL AEROPLANE XXVI. APPARATUS FOR SIMPLE SCIENTIFIC EXPERIMENTS XXVII. A RAIN GAUGE XXVIII. WIND VANES WITH DIALS XXIX. A STRENGTH-TESTING MACHINE XXX. LUNG-TESTING APPARATUS XXXI. HOME-MADE HARMONOGRAPHS XXXII. A SELF-SUPPLYING MATCHBOX XXXIII. A WOODEN WORKBOX XXXIV. WRESTLING PUPPETS XXXV. DOUBLE BELLOWS XXXVI. A HOME-MADE PANTOGRAPH XXXVII. A SILHOUETTE DRAWING MACHINE XXXVIII. A SIGNALLING LAMP XXXIX. A MINIATURE GASWORKS

THINGS TO MAKE.

I. A SAWING TRESTLE

A strong and stable sawing trestle is one of the most important accessories of the carpenter’s shop, whether amateur or professional. The saw is constantly being used, and for it to do its work accurately the material must be properly supported, so that it cannot sway or shift. Anybody who has been in the habit of using a wobbly chair or box to saw on will be surprised to find how much more easily wood can be cut when resting on a trestle like that illustrated by Figs. 1 to 3.

The top, _a_, of the trestle is 29 inches long, 4 inches wide, and 2 inches thick. At one end it has a deep nick, to serve much the same purpose as the notched board used in fretworking; also to hold on edge such things as doors while their edges are planed up. Pushed back against the wall the trestle is then “as good as a boy.”

[Illustration: Fig I.—Leg of sawing trestle (left). Trestle seen from above (right).]

The four legs are made of 2 by 2 inch stuff. To start with, the pieces should be 24 inches long, to allow for the waste of cutting on the angle.

Cutting the Notches.—Make four marks 7 inches from the four corners of the top, set your bevel to an angle of 70 degrees (or cut an angle out of a card with the help of a protractor), and lay a leg against each mark in turn, the end projecting an inch or so above the top. Move the leg about till it makes the proper angle at the mark, and draw a pencil line down each side of the leg as close up as possible. Since the legs may vary slightly in size, use each once only for marking, and number it and the place to which it belongs.

Lines must now be drawn along the upper and under sides of the top, parallel to and 3/4-inch from the edge, to complete the marking out of the notches.

Cut just inside the side marks with a fine tenon saw, and remove the wood between the cuts back to the top and bottom marks with a broad, sharp chisel, making the surface of the cut as true and flat as you can. Then “offer” the leg that belongs to the cut, its end projecting an inch or so. If it won’t enter, bevel off the sides of the cut very slightly till it will. A good driving fit is what one should aim at. While the leg is in place, draw your pencil in the angles which it makes with the top above and below, to obtain the lines AB, CD (Fig. 2, a).

Bevelling the Legs.-The marking out of the bevels will be much expedited if a template is cut out of tin or card. It should be just as wide as the legs, and at a point 4 inches from one end run off at an angle of 162 degrees from one edge. (See Fig. 2,b.)

[Illustration: FIG. 2.-Showing how to cut sloping joint for trestle leg.]

Draw with a square a line, EEl, across what is to be the inside of the leg. The template is applied to the end side of the leg and moved up till its sloping edge occupies a position in which a perpendicular dropped on to it from C is 1/2 inch long. Mark the line EF (Fig. 2, b) and the perpendicular CG. The bevel is marked on the other side of the leg, the, angle of the template being at E1 (Fig. 2, a) to guide the saw, which is passed down through the leg just outside the marks till in line with CD. The piece is detached by a cross cut along CG, CD. This procedure, which sounds very complicated, but is really very simple, and performed much more quickly than it can be described, yields a leg properly bevelled and provided with a shoulder to take the weight of the top.

[Illustration: Fig.3—End elevation of sawing trestle.]

The leg at the diagonally opposite corner is an exact replica of the one first made; the other two are similar, but the direction of the bevels is reversed, as will be evident after a little consideration.

When all the legs are ready, knock them into place, driving the shoulders tight up against the top, and nail them on. The projections are sawn off roughly and planed down flush with the top. Then affix the tie C at each end, and plane its edges off neatly.

Truing the Legs.—Stand the stool on end, top flat against the wall. Measure off a 20-inch perpendicular from the wall to the outside corner of each of the two upper legs. (Fig. 3.) Lay a straightedge from mark to mark, and draw lines across the legs. Reverse the trestle, and do the same with the legs at the other end. Then turn the trestle on its side, and draw lines on the other outside faces of the legs, using the lines already made as guides. If the operation has been carried through accurately, all eight lines will be in a plane parallel to the top. Cut off the ends of the legs below the lines, and the trestle is finished.

II. A JOINER’S BENCH.

After finishing his sawing trestle the reader may be willing to undertake a larger job, the manufacture of a joiner’s bench—if he does not already possess a good article—heavy and rigid enough to stand firm under plane and hammer.

For the general design and detailed measurements he is referred to Figs. 4 and 5, in which the dimensions of each part are figured clearly. The length of 5 feet, width of 2 feet (exclusive of the back E), and height of 2 feet 7-1/2 inches will be found a good average. If the legs prove a bit long for some readers, it is a simple matter to lay a plank beside the bench to raise the (human) feet an inch or two.

In order to give rigidity, the struts S1S2 of the trestles at the end and the braces DD on the front are “halved” where they overlap the legs and front so as to offer the resistance of a “shoulder” to any thrust.

[Illustration: Fig. 4.—Front elevation of Joiner’s bench]

Materials.—The cost of these will be, approximately: wood, 12s. 6d.; [12 Shillings. 6 Pence] bench screw, 1s. 6d.; nails and screws, 1s.; or 15s. in all. It is advisable to show the timber merchant the specifications, so that he may cut up the stuff most economically.

If the wood is mill-planed before delivery a lot of trouble will be saved, as no further finish will be required, except perhaps at the top corners. In passing, one should remark that the boards used should be of the widths and lengths given; while as regards thickness the figures must be taken as nominal, as in practice the saw cut is included. Thus a 1-inch board would, when planed, be only 7/8 to 15/16 inch thick, unless the actual size is specified, in which case something extra might be charged.

Construction.

The Trestles.—These should be made first. Begin by getting all the legs of exactly the same length, and square top and bottom. Then cut off two 22-inch lengths of the 6 by 1 inch wood, squaring the ends carefully. Two of the legs are laid on the floor, one end against the wall or a batten nailed to the floor and arranged parallel to one another, as gauged by the piece C, which is nailed on perfectly square to both, and with its top edge exactly flush with the ends of the legs.

Next take the 3 by 1 inch wood for the struts, and cut off a piece 32 inches long. Two inches from one end of it make a cross mark with the square, and from the ends of the mark run lines towards the end at an angle of 45 degrees. Cut along these lines, and lay one of the edges just cut up against C, and flush with the outer edge of L1 (Fig. 5). Tack the strut on temporarily to both legs, turn the trestle over, and draw your pencil (which should have a sharp point) along the angles which the strut makes with the legs. This gives you the limits of the overlaps. Detach the strut.

The marking-gauge now comes into use. Set it at 3/8 inch, and make marks on the sides of the strut down to the limits, pressing the guide against what will be the inner face of the board. The ends must now be divided down along the gauge scratches to the limit mark with a tenon or panel saw, the saw being kept on the inside of the mark, So that its cut is included in the 3/8 inch, and a cross cut made to detach the piece and leave a shoulder. The strut is “offered” again to the legs, and a mark is drawn across the bottom parallel to the ends or the legs for the final saw cut. Nail on the strut, pressing the legs well up against the shoulders. Its fellow on the other side of the legs is prepared in exactly the same manner; and the second trestle is a duplicate of the first, with the exception that the directions of the struts are reversed relatively to the C piece, to preserve the symmetry—which, however, is not an important point.

[Illustration: FIG. 5.—End elevation of joiner’s bench.]

Back and Front.—The only operation to be performed on the front piece B and the back G is the notching of them both on the inside faces at the centre to take the ends of the bearer F, which performs the important function of preventing any bending of the top planks. Lay the boards together, top edges and ends level, and mark them at the same time. The square is then used on the faces to give the limits for the notches, which should be 1/4 inch deep and chiselled out carefully.

Draw cross lines with your square 3 inches from each end of both pieces, on the inside, to show where the legs are to be. Bore holes in the boards for the 3-inch screws which will hold them to the legs.

Attaching the Trestles.—Stand the trestles on their heads and lay the back and front up to them, using the guide marks just drawn. A nail driven part way in through one of the screw holes, and a batten tacked diagonally on the DD lines, will hold a leg in position while the screws are inserted. (Make sure that the tops of the legs and the top edges of B and G are in the same plane.)

Affixing the Braces.—The braces DD, of 3 by 1 inch stuff, can now be marked off and cut exactly down the middle to the limits of the overlap. Screw on the braces.

The bearer F is next cut out. Its length should be such as to maintain the exact parallelism of B with G, and the ends be as square as you can cut them. Fix it in position by two 2-inch screws at each end.

The bench is now ready for covering. Begin with the front board, A1. Bore countersunk holes for 3-inch screws over the centre of the legs and half an inch from the front edge, 1 foot apart. Arrange Al with its front edge perfectly flush with the face of B, and tack it in place by nails driven through a couple of screw holes, and insert all the screws. The middle board, A2, is laid up against it, and the back board, A3 (bored for screws like the front board), against that. Screw down A3.

You must now measure carefully to establish lines over the centres of CC and F. Attach each board to each of these by a couple of screws. All screws in the top of the bench are countersunk 1/8 inch below the surface. Screw the ledge E, of 4 by 5/8 inch wood, on to the back of G, with 2-1/2 inches projecting. This will prevent tools, etc., slipping off the bench.

[Illustration: Fig. 6.—Perspective view of joiner’s bench]

The Vice.—This important accessory consists of an 8 by 2 by 15 inch piece, V, a 2-inch diameter wooden bench screw and threaded block, and a guide, F. (Note.—A 1-1/8-inch diameter wrought iron screw is very preferable to the wooden, but its cost is about 4s. more.) V should be tacked to B while the 2-inch hole for the bench screw is bored through both with a centre bit, at a point 8 inches from the guide end on the centre line of V. This hole must be made quite squarely to enable the screw to work freely. If a 2-inch bit is not available, mark out a 2-inch ring and bore a number of small holes, which can afterwards be joined by a pad-saw; and finish, the hole thus formed with a half-round rasp. The threaded block for the screw is attached to the inner side of H in the angle formed by the leg and the board A1. The guide F is then fitted. This is pinned in to V, and the slides through B. If a rectangular piece is used, cut the hole in V first; then screw V up tightly, and mark B through V. It may be found more convenient to use a circular piece, in which case the holes for it can be centre-bitted through V and B in one operation. If after fitting V projects above A, plane it down level.

The finishing touches are rounding off all corners which might catch and fray the clothes, and boring the 3/4-inch holes, HH, for pegs on which planks can be rested for edge planing.

For a “stop” to prevent boards slipping when being planed on the flat, one may use an ordinary 2-inch wood screw, the projection of which must of course be less than the thickness of the board planed. Many carpenters employ this very simple expedient; others, again, prefer a square piece of wood sliding stiffly through a hole in A1 and provided on top with a fragment of old saw blade having its teeth projecting beyond the side facing the work. The bench is countersunk to allow the teeth to be driven down out of the way when a “clear bench” is required.

Just a word of warning in conclusion. Don’t be tempted to nail the parts together—with the exception of the trestle components—to save trouble. The use of screws entails very little extra bother, and gives you a bench which can be taken to pieces very quickly for transport, and is therefore more valuable than a nailed one.

III. A HANDY BOOKSTAND.

A bookstand of the kind shown in Fig. 7 has two great advantages: first, it holds the books in such a position that their titles are read more easily than when the books stand vertically; second, it can be taken to pieces for packing in a few moments, as it consists of but four pieces held together by eight removable wedges. We recommend it for use on the study table.

Oak or walnut should preferably be chosen as material, or, if the maker wishes to economize, American whitewood or yellow pine. Stuff 1/4 inch (actual) thick will serve throughout if the stronger woods are used; 3/8 inch for the shelf parts in the case of whitewood or pine.

The ends (Fig. 8) are sawn out of pieces 5-1/2 by 10 inches, and nicely rounded off on all but the bottom edge, which is planed flat and true. The positions for the holes through which the shelf eyes will project must be marked accurately, to prevent the stand showing a twist when put together. The simplest method of getting the marks right is to cut a template out of thin card and apply it to the two ends in turn, using the base of each as the adjusting line. Fret-saw the holes, cutting just inside the lines to allow for truing up with a coarse file.

[Illustration: Fig. 7.—Perspective view of bookstand.]

The shelves a and b are 15 inches long, exclusive of the lugs c, c, c, c, and 4-1/2 and 4-3/4 inches wide respectively. As will be seen from Fig. 8, b overlaps a. Both have their top edges rounded off to prevent injury to book bindings, but their bottom edges are left square.

As the neatness of the stand will depend largely on a and b fitting closely against the sides, their ends should be cut out and trued carefully, special attention being paid to keeping the shoulders between and outside the lugs in a straight line. The wedge holes in c, c, c, c measure 1/2 by 1/4 inch, and are arranged to be partly covered by the sides, so that the wedges cannot touch their inner ends. (See Fig. 9.) This ensures the shelves being tightly drawn up against the sides when the wedges are driven home.

[Illustration: Fig. 8.—End elevation of bookstand.]

The wedges should be cut on a very slight taper of not more than half an inch in the foot run, in order to keep their grip. Prepare a strip as thick as the smaller dimension of the holes, 3/8 inch wide at one end, and 7/8 inch wide at the other. Assemble the parts and push the piece through a hole until it gets a good hold, mark it across half an inch above the hole, and cut it off. Then plane the strip down parallel to the edge that follows the grain until the end will project half an inch beyond the lug next fitted. Mark and cut off as before, and repeat the process until the eight wedges are ready in the rough. Then bevel off the outside corners and smooth them—as well as the rest of the woodwork—with fine glass paper.

Shelves and sides should be wax-polished or given a coat or two of varnish.

[Illustration: Fig. 9. Plan or bookstand shelf.]

Don’t drive the wedges in too tight, or yon may have to lament a split lug.

If the stand is to be used for very heavy books, or the shelves are much longer than specified here, it is advisable to bring the angle of the shelves down to the bottom of the standards, to relieve the shelves of bending strain at the centre; or to use stouter material; or to unite the shelves at two or three points by thin brass screws inserted through holes drilled in the overlapping part.

IV. A HOUSE LADDER.

The preparation and putting together of the parts of a ladder having round, tapered rungs let into holes in the two sides is beyond the capacity of the average young amateur; but little skill is needed to manufacture a very fairly efficient substitute for the professionally-built article—to wit, a ladder of the kind to which builders apply the somewhat disparaging adjective “duck.”

The rungs of such a “duck” ladder are merely nailed to the outside if the ladder is required for temporary purposes only; but as we are of course aiming at the construction of a thing made to last, we shall go to the trouble of “notching-in” each rung (see Fig. 10), so that the sides shall take the weight directly, and the nails only have to keep the rungs firmly in position. The objection to notching-in is that it reduces the strength of the ladder, which is of course only that of the wood between the bottom of the notches and the plain side. Therefore it is necessary to have sides somewhat deeper than would be required for a centrally-runged ladder; which is pierced where the wood is subjected to little tension or compression.

[Illustration: Fig. 10—House ladder and details of letting in a rung]

Materials.—The length of the ladder will decide what the stoutness of the sides should be. For a ladder about 12 feet long, such as we propose to describe, larch battens 3 by 1-1/8 inches (actual) in section and free from knots, especially at the edges, will be sufficiently strong to carry all reasonable weights without danger of collapse. But be sure to get the best wood obtainable. The rungs may be of 2 by 1 inch stuff, though 2 by 3/4 inch will suffice for the upper half-dozen, which have less wear, and are shorter than those below.

The rungs are 10 inches apart (Fig. 10), centre to centre. The distance may be increased to a foot, Or even more if weight-saving is an object.

CONSTRUCTION.

Preparing the Sides.—These are cut to exactly the same length, which we will assume to be 11 feet 6 inches, planed quite smooth and rounded off slightly at the corners to make handling comfortable. Before marking them for the rungs it is important that they shall be so arranged that both incline equally towards a centre line.

Stretch a string tightly three inches above the ground, and lay the sides of the ladder on edge to right and left of it, their ends level. Adjust the bottom ends 8-1/2, the top ends 6-1/2 inches from the string, measuring from the outside. Tack on cross pieces to prevent shifting, and then, starting from the bottom, make a mark every 10 inches on the outside corners, to show the position of the tops of the rungs. A piece of the wood to be used for making the rungs of is laid up to the pairs of marks in turn, and lines are drawn on both sides of it.

Cutting the Notches.—The work of marking the ends of the notches will be quickened, and rendered more accurate, if a template (Fig. 10) is cut out of tin. The side AC is 3/8 to 1/2 inch deep. Apply the template to both faces of the side in turn, with its corner A at the line below the rung, and DE flush with the upper corner. When all the notches have been marked cut down the AC line of each with a tenon saw, and chisel along BC till the wedge-shaped chip is removed. Finish off every notch as neatly as possible, so that the rungs may make close contact and keep water out.

Preparing the Rungs.—Lay a piece of rung batten across the lowest notches, the end overhanging the side by a quarter of an inch or so to allow for the taper of the ladder, and draw your pencil along the angles which it makes with the sides. Mark the positions of the nail holes. Cut off the rung at the cross lines; drill the four nail holes on the skew, as shown in Fig. 10; and round off all the corners. The other rungs are treated in the same manner, and the sides are then separated, for the inside top corner and both back corners, which will be handled most, to be well rounded off and rubbed smooth with glass paper.

Assembling.—Before putting the parts together give them a coating of paint, as the contact surfaces will not be accessible to the brush afterwards. When the paint has dried, lay the sides out as before, and nail on the rungs with 3-inch nails. To counteract any tendency of the sides to draw apart, a light cross bar should be fixed on the back of the ladder behind the top and bottom rungs.

Round off the end angles of the rungs, and apply a second coating of paint.

Note.—A ladder of this kind is given a more presentable appearance if the rungs are let in square to the sides and flush, but at the sacrifice either of strength or lightness, unless narrow rungs of a hard wood, such as oak, be used. Moreover, square notches are not so easy to cut out as triangular.

For a short ladder, not more than 9 feet long, the section of the sides may safely be reduced to 2-3/4 by 1 inch (actual), if good material is selected.

V. A DEVELOPING SINK.

Many amateur photographers are obliged to do their developing in odd corners and under conditions which render the hobby somewhat irksome if a large number of plates have to be treated. The main difficulty is to secure an adequate water supply and to dispose of the waste water. At a small expenditure of money and energy it is easy, however, to rig up a contrivance which, if it does not afford the conveniences of a properly equipped dark room, is in advance of the jug-and-basin arrangement with which one might otherwise have to be content. A strong point in favour of the subject of this chapter is that it can be moved without any trouble if the photographer has to change his quarters.

The foundation, so to speak, of the developing sink is a common wooden washstand of the kind which has a circular hole in the top to hold the basin. A secondhand article of this sort can be purchased for a shilling or two. A thoroughly sound specimen should be selected, even if it is not the cheapest offered, especial attention being paid to its general rigidity and the good condition of the boards surrounding the basin shelf.

[Illustration: Fig. 11.—A home-made developing sink for the darkroom.]

The area of the top is generally about 20 by 15 inches; but if a stand of larger dimensions can be found, choose it by preference.

The general design of the sink and its equipment is shown in Fig. 11. For the uprights, which rest on the beading of the washstand, use two boards 9 inches wide, 1/2 inch (actual) thick, and 36 inches long. The top shelf, to carry the pail or other water container, should be of 1-inch stuff; and the two lower shelves be not more than 5 inches wide and 3/4 inch thick. Space the shelves at least 11 inches apart, so that they may accommodate tall bottles. The superstructure will gain in rigidity if the intermediate shelves are screwed to the uprights, in addition to being supported on ledges as indicated; and if the back is boarded over for at least half its height, there will be no danger of sideways collapse, when a full bucket is put in position.

The top of the washstand, on which the developing will be done, must be provided with a tray of lead or zinc. Lead is preferable, as lying flatter; but the jointing at the corners is more difficult than the soldering of sheet zinc, which, though more liable to chemical corrosion, is much lighter than the thinnest lead—weighing about 1-1/2 lbs. to the square foot—that could well be used. If lead is selected, the services of a plumber had better be secured, if the reader has had no experience in “wiping a joint.”

A zinc tray is prepared by cutting out of a single sheet a piece of the shape shown in Fig. 12. The dimensions between the bending lines (dotted) are 1/8 inch less in both directions than those of the shelf. The turn-ups a, a, b, b, should not be less than 1-1/2 inches wide. Allow half an inch at each end of b b for the turnover c. Turn a a up first, then b b, and finally bend c c round the back of a a, to which they are soldered. A drop of solder will be needed in each corner to make it water-tight. When turning up a side use a piece of square-cornered metal or wood as mould, and make the angles as clean as possible, especially near the joints.

[Illustration: FIG. 12.—Showing how the tray for sink is marked out.]

A drain hole, an inch or so in diameter, is cut in the centre of the tray. To prevent the hands being injured by the tray, the front should be covered by a 1/2-inch strip of zinc doubled lengthwise, or be made a bit deeper than 1-1/2 inches in the first instance and turned over on itself.

Before the tray is put in position the basin hole must be filled in, except for an opening to take the waste pipe. The plug is pad-sawed out of wood of the same thickness as the top, to which it is attached by crossbars on the under side. The whole of the woodwork, or at least those parts which are most likely to get wetted, should then be given a coat or two of paint.

A waste pipe, somewhat larger than the drain hole and 3 inches long, having been firmly soldered to the tray, beat the edges of the hole down into the pipe. Then prepare a wooden collar to fit the pipe outside, and drill a hole on the centre line to take a carpenter’s screw. If the edges of the tray are supported on slats 3/16 to 1/4 inch thick, and its centre is kept in contact with the wood by the collar pressing against the underside of the shelf, any water will naturally gravitate to the centre and escape by the waste pipe. This automatic clearance of “slops” is a very desirable feature of a developing sink.

To prevent water splashing on to the sides of the stand and working down between tray and wood, tack pieces of American cloth on the sides with their edges overlapping the tray edges by an inch or so.

A small two-handled bath is the most convenient receptacle for the waste water. It should hold at least a quarter as much again as the water tank, so as to avoid any danger of overfilling. A piece of old cycle tyre tubing, tied to the waste pipe and long enough to reach below the edge of the bath, will prevent splashing—which, when chemicals are being poured away, might prove disastrous to light-coloured clothes.

The supply pipe has a siphon-piece of “compo” tubing at the top, to draw off the water when the tube has been filled by suction, and a small tap at the bottom. This tap, when not in use, should be held back out of the way by a wire hook attached to the lowest of the upper shelves. A piece of linoleum should be cut to fit the bath-shelf and protect the drawer below.

VI. A POULTRY HOUSE AND RUN.

This chapter should be of interest to the keeper of poultry on a small scale, for even if the instructions given are not followed out quite as they stand, they may suggest modifications to suit the taste and means of the reader.

The principle of the combined run and house—which will accommodate a dozen fowls without overcrowding, especially if it be moved from time to time on to fresh ground—will be understood from Figs. 13 and 14. The first of these shows the framework to which the boards for the house and the wire for the run are nailed. Its over-all length of 10 feet is subdivided into five “bays” or panels, 2 feet long (nearly) between centres of rafters. Two bays are devoted to the house, three to the run.

[Illustration: Fig. 13.—Frame for poultry house and run (above). Completed house and run (below).]

One square (10 by 10 feet) of weather boarding 6 inches wide, for covering in the house. 44 feet of 4 by 1, for base and ridge. 56 feet of 3 by 1, for eight rafters. 28 feet of 3 by 1-1/2, for four rafters. 50 feet of 2 by 1-1/2, for door frames and doors. 6 feet of 2 by 2, for tie t. 45 feet of 2-foot wire netting. Two pairs of hinges; two locks; staples, etc.

The materials used comprise:— The total cost as estimated from prices current at the time of writing is 25s. This cost could be considerably reduced by using lighter stuff all through for the framework and doors and by covering in the house with old boards, which may be picked up cheaply if one is lucky. Whether it is advisable to sacrifice durability and rigidity to cost must be left to the maker to decide. Anyhow, if the specifications given are followed, an outfit warranted to last for several years will be produced.

A Few Points.—The vertical height of the run is just under 6 feet, the tips being cut away from the rafters at the apex. The width at the ground is exactly 6 feet. The base angles made by AA with B (Fig. 14) are 63 degrees; that which they make with one another, 54 degrees. The rafters r1 and r3 at each end of the house are half an inch thicker than the rest, as they have to stand a lot of nailing.

CONSTRUCTION.

Cutting the Rafters.—If floor space is available, chalk out accurately the external outline of a pair of rafters (80 inches long each before shaping) and a line joining their lower ends. Then draw a line bisecting the ridge angle. With this template as guide the rafters can be quickly cut to shape. Another method is to cut one rafter out very carefully, making a notch for half the width of the ridge, and to use it as a pattern for the rest. In any case the chalked lines will prove useful in the next operation of pairing the rafters and uniting them by a tie just under the ridge notch. Cut a 4 by 1 inch notch at the bottom of each rafter, on the outside, for the base piece. The two end pairs have the B pieces (Fig. 14) nailed on to them, and r3 the tie t, which should be in line with the rafters. The other three pairs require temporary ties halfway up to prevent straddling during erection.

Door Frames and Doors.—The method of fixing the frame of the door at the run end is shown in Fig. 14. The material for the frame being 1/2 inch thicker than that of the rafters, there is room for shoulders at the top angles, as indicated by dotted lines. The door frame at the house end is of the same thickness as r1 so that no overlapping is possible. This being the case, screws should be used in preference to nails, which are liable to draw a sloping face out of position as they get home.

[Illustration: Fig. 14.—On left, elevation of end of run; on right, door for run.]

The doors are made of 2 by 2 inch stuff, halved at the corners. Cut out the top and bottom of the two sides; lay them on the floor so as to form a perfect rectangle, and nail them together. The strut is then prepared, care being taken to get a good fit, as any shortness of strut will sooner or later mean sagging of the door. Cut the angles as squarely as possible, to ensure the strut being of the same length both inside and out.

Note.—As the door is rectangular, it does not matter which corners are occupied by the ends of the strut; but when the door is hung, the strut must run relatively to the side on which the hinges are, as shown in Fig. 14. Amateurs—even some professionals—have been known to get the strut the wrong way up, and so render it practically useless.

Covering the Ends of the House.—The ends of the house should be covered before erection, while it is still possible to do the nailing on the flat. The run end is boarded right over, beginning at the bottom, and allowing each board to overlap that below it by 1 inch. The board ends are flush with the outer sides of the rafters. When boarding is finished, cut (with a pad saw) a semicircular-topped run hole, 14 inches high and 8 inches wide, in the middle of the bottom. Any structural weakness caused by severing the two lowest boards is counteracted by the two grooved pieces in which the drop-door moves.

Odds and ends of weather boards should be kept for the door end of the house, which requires short pieces only, and is not boarded below the top of b2. The door may be weather-boarded to match the rest of the end, or covered by a few strakes of match-boarding put on vertically.

The two base pieces, b1 and b2, and the ridge should be marked off for the rafters at the same time. All three are 10-foot lengths of 4 by 1 wood, unless you prefer the ridge to project a bit, in which case you must allow accordingly.

Stand all three pieces together on edge, and make the marks with a square across the tops. Allow a distance of 4 feet between the outside faces of r1 and r3; halve this distance to get the centre of r2; and subdivide the distance between r3 and r6 so that each rafter is separated from its neighbours by an equal space, which will be 1 foot 11 inches. Number the marks and continue them down the sides of the boards with the square. There should be a mark on each side of the place to be occupied by the intermediate rafters, to prevent mistakes; for it is obvious that if a rafter is fixed on the left side of a single ridge mark and on the right of the corresponding mark on the base, the result will not be pleasing.

Erection.—The services of a second pair of hands are needed here, to hold while nailing is done. Nail holes having been drilled in the tops of the rafters and in the base pieces, the ends are stood upright and tacked to the ridge at the places marked for them, and after them the intermediate rafters, working from one end to the other. Then tack on the base pieces, b1, b3. Get the ends quite perpendicular, and nail a temporary cross strut or two on the outside of the rafters to prevent shifting while the final nailing up is done.

Covering the Shed.—Sixteen boards, 4 feet 2 inches long, are needed for each side, as, owing to the overlap of one inch, each tier covers only five of the 80 inches. The ridge is made watertight by a strip of sheet zinc, a foot wide, bent over the top and nailed along each edge.

Waterproofing.—All the woodwork should now be given a coating of well-boiled tar, paint, creosote, or some other preservative, worked well down into the cracks. Creosote and stoprot are most convenient to use, as they dry quickly.

Netting.—When the preservative has dried, fix on the netting with 3/4-inch wire staples. Begin at the base on one side, strain the netting over the ridge, and down to the base on the other side. Be careful not to draw the rafters out of line sideways. The last edge stapled should be that on the roof of the house.

Note.—When driving nails or staples into a rafter or other part, get a helper to hold up some object considerably heavier than the hammer on the farther side to deaden the blow. Lack of such support may cause damage, besides making the work much more tedious and difficult.

Finishing off.—The doors are now hung, and fitted with buttons and padlocks. The stops should be on the doors, not on the frames, where they would prove an obstruction in a somewhat narrow opening. Perches should be of 2 by 1 inch wood, rounded off at the top, and supported in sockets at each end so as to be removable for cleaning; and be all on the same level, to avoid fighting for the “upper seats” among the fowls. A loose floor, made in two pieces for convenience of moving, will help to keep the fowls warm and make cleaning easier, but will add a few shillings to the cost. The inside of the house should be well whitewashed before fowls are admitted. To prevent draughts the triangular spaces between the roof boards and rafters should be plugged, but ample ventilation must be provided for by holes bored in the ends of the house at several elevations, the lowest 2 feet above the base. Handles for lifting may be screwed to the faces of b and b2 halfway between the door frame and the corners.

VII. A SHED FOR YOUR BICYCLE.

The problem, how to house one or more cycles, often gives trouble to the occupiers of small premises. The hall-way, which in many cases has to serve as stable, is sadly obstructed by the handles of a machine; and if one is kept there, the reason generally is that no other storage is available.

If accommodation is needed permanently for two or three cycles belonging to the house, and occasionally for the machine of a visitor, and if room is obtainable in a backyard or garden in direct communication with the road, the question of constructing a really durable and practical cycle shed is well worth consideration. I say constructing, because, in the first place, a bought shed costing the same money would probably not be of such good quality as a home-made one; and secondly, because the actual construction, while not offering any serious difficulty, will afford a useful lesson in carpentry.

[Illustration: FIG. 16.—Cycle shed completed.]

Cycle sheds are of many kinds, but owing to the limitations of space it is necessary to confine attention to one particular design, which specifies a shed composed of sections quickly put together or taken apart—portability being an important feature of “tenants’ fixtures”—and enables fullest advantage to be taken of the storage room. As will be seen from the scale drawings illustrating this chapter, the doors extend right across the front, and when they are open the whole of the interior is easily accessible. The fact that the cycles can be put in sideways is a great convenience, as the standing of the machines head to tail alternately economizes room considerably.

[Illustration: FIG. 16.—Plan of corner joints of cycle shed.]

I ought to mention before going further that the shed to be described is very similar, as regards design and dimensions, to one in a back issue of Cycling. By the courtesy of the proprietors of the journal I have been permitted to adapt the description there given.[1]

[Footnote 1: By Mr. Hubert Burgess. ]

Dimensions and General Arrangements.—The shed is 8 feet long over all, 5 feet 6 inches high in front, 5 feet high at the back, 3 feet deep over all, under the roof, which projects 3 inches fore and aft, and 2 inches at each end. It consists of seven parts: two sides, roof, back, front frame and doors, and a bottom in two sections.

The reader should examine the diagrams (Figs. 16 to 24) to get a clear understanding of the disposal of the parts at the corners. Fig. 16 makes it plain that the frames of the back and front overlap the frames of the sides, to which they are bolted; and that the covering of the back overlaps the covering of the sides, which in turn overlaps the front frame.

All corner joints are halved. In order to allow the doors to lie flush with the front of the doorframe uprights, the last must project the thickness of the door boards beyond the frame longitudinals; and to bring the front uprights of the sides up against the uprights of the door frame, the longitudinals are notched, as shown (Fig. 16), to the depth of the set-back for the doors.

Materials.—The question of cost and the question of materials cannot be separated. A shed even of the dimensions given consumes a lot of wood, and the last, that it may withstand our variable and treacherous climate for a good number of years, should, as regards those parts directly exposed to the weather, be of good quality. Yellow deal may be selected for the boards; pitch pine is better, but it costs considerably more. For the frames and non-exposed parts generally ordinary white deal will suffice.

[Illustration: FIG. 17.-Types of match boarding: (a) square joint; (b) double.-V; (c) single-V.]

The scale drawings are based on the assumption that matching of one of the forms shown in Fig. 17, and measuring 4 inches (actual) across, exclusive of the tongue, and 5/8 inch (actual) thick, is used.

As advised in the case of the carpenter’s bench, (p. 15) the prospective constructor should let the wood merchant have the specifications, so that he may provide the material in the most economical lengths. The following is a rough estimate of the wood required, allowing a sufficient margin for waste:

4-1/2 (over tongue) by 5/8 inch (actual) yellow match boarding for sides, roof, back, and doors:

1-1/2 squares = 150 sq. feet. = 450 feet run. White 4-1/2 by 3/4 inch square-shouldered flooring: 1/4 square = 25 sq. feet. = 75 feet run. 3 by 1-1/2 inch battens = 88 feet run. 4 by 1-1/2 inch battens = 26 feet run. 3 by 2 inch battens = 27 feet run. 5 by 1-1/2 inch battens = 8 feet run. 2 by 1-1/2 inch battens = 21 feet run.

There will also be required: Twelve 6-inch bolts and nuts. Two pairs 18-inch cross-garnet hinges. Two door bolts. One lock (a good one). Four yards of roofing felt. Two gallons of stoprot. Three lbs. wire-nails A few dozen 3-inch and I-1/2-inch screws.

The total cost of the materials will come to about 2 pounds, 2s.

CONSTRUCTION.

The scale drawings are so complete as to dimensions that, assuming the materials to be of the sizes specified, they may be followed implicitly. It is, of course, easy to modify the design to suit any slight differences in dimensions; and to avoid mistakes all the stuff should be gauged carefully beforehand.

[Illustration: FIG. 18.-Side of cycle shed.]

The Sides.—When laying out the frames for these it is necessary to bear in mind that the front upright is somewhat less than 5 feet 6 inches long, and the back upright rather more than 5 feet, owing to the slope of the roof, and to the fact that they are set in 2 inches from the back and front. To get the lengths and angle of the half-joints right, lay the verticals, which should be 5 feet 6 inches and 5 feet 1 inch long before trimming, on the floor, at right angles to the bottom of the frame (2 feet 7-3/4 inches long) and quite parallel to one another. (We will assume the half-joints to have been made at the bottom.) The batten for the top is laid across the ends of the verticals, its top edge in line with a 5-foot 6-inch mark at a point 2 inches beyond the front vertical, and with a 5-foot mark 2 inches beyond the back vertical, the distances being measured perpendicularly from the bottom of the frames produced. The lines for the joints can then be marked, and the joints cut. The notches for the roof stays should not be cut till the roof is being fitted.

[Illustration: FIG. 19.—Boards at top of side, fixed ready for cutting off.]

Use the side frame first made as template for the other.

The shelves are notched at the ends, so that their back faces shall be flush with the board side of the frame.

Fix the corners with the screws, and plane off the projecting angles of the uprights.

When putting on the boards, start at the back of the frame. Plane down the groove edge of the first board until the groove is out of the board, and apply the board with 1-1/2 inches projecting beyond the frame. Leave a little spare at each end of every board, and when the side is covered run a tenon-saw across both ends of all the boards close to the frame, and finish up with the plane. This is quicker and makes a neater job than cutting each board to size separately.

[Illustration: FIG. 20.-Back of cycle shed.]

The Back (Fig. 20).—When laying out the frame for this, remember that there is a bevel to be allowed for along the top, and that the height of the frame at the front must be that of the back of a side frame. (See Fig. 21.) The boards should be cut off to the same slope.

Twenty-four boards should exactly cover the back. Cut the tongue neatly off that last fixed, and glue it into the groove of the first board.

The Front.—The frame requires careful making. For details of corner joints see Fig. 16. The 3-inch faces of the top and bottom bars are vertical. The upper side of the top bar is planed off to the angle of the slope. (Fig. 23.)

[Illustration: FIG. 21. Detail of eaves.]

The Doors (Fig. 22).—These are the most difficult parts to construct, as the braces which prevent the front edges dropping must be carefully fitted in order to do their work properly.

The eleven outside boards of each door are held together by two 4-inch ledges 6 inches away from the ends, and one 5-inch central ledge. Allow a little “spare” on the boards for truing up. Boards and ledges having been nailed together, lay a piece of 4 by 1-1/2 inch batten across the ledges on the line which the braces will take, and mark the ledges accordingly. Next mark on the batten the ends of the braces. These project half an inch into the ledges, and terminate on the thrust side in a nose an inch long, square to the edge of the brace. The obtuse angle is flush with the edge of the ledge. Cut out the braces, lay them in position on the ledges, and scratch round the ends. Chisel out the notches very carefully, working just inside the lines to ensure the brace making a tight fit. If there is any slackness at either end, the brace obviously cannot carry the weight of the door until the door has settled slightly, which is just what should be prevented. Therefore it is worth while taking extra trouble over this part of the work.

[Illustration: FIG. 22.-Doors of shed.]

Cautions.—Don’t get the nose of the brace too near the end of the ledge. Nail the boards on specially securely to the ledges near the ends of the braces.

Fitting the Doors.—The doors should now be laid on the top of the frame and secured to it by the four hinges. The long ends of these are held by screws driven through the boards into the bearers; the cross pieces are screwed to the uprights of the door frame. The doors when closed should make a good but not tight fit with one another.

PUTTING THE PARTS TOGETHER.

The two sides, front, and back are now assembled, on a level surface, for drilling the holes for the bolts which hold them together. The positions of the bolts will be gathered from the drawings. Get the parts quite square before drilling, and run the holes through as parallel to the sides as possible. If the bolts are a bit too long, pack washers between nut and wood until the nut exerts proper pressure.

Caution.—The hole must not be large enough to allow the square part just under the head to revolve, for in such a case it would be impossible to screw up the nut. Its size ought to be such as to require the head to be driven up against the wood.

[Illustration: Fig. 23 Roof attachment]

The Roof.—The boards of this are attached to a frame which fits closely inside the tops of the sides, back, and front. To get the fit of the frame correct, it must be made a bit too wide in the first instance, and then be bevelled off at the front, as shown in Fig. 23, and the reverse way at the back. The ends are notched for the stays AA, and the frame then tacked firmly, by driving nails into the sides, etc., below it, in the position which it will occupy when the roof is on, except that it projects upwards a little. Cut off twenty-five boards 3 feet 7 inches long. Omitting the end ones for the present, lay the remainder up to one another in order, their ends an equal distance from the frame, and nail to the frame. Lift off the roof, insert and secure AAAA, and nail on the end boards. Then rule parallel straight lines 3 feet 6 inches apart across all the boards from end to end of the roof, and cut along these lines. The roof is replaced after notches have been cut in the tops of the sides to take AAAA, and secured to the vertical parts by six bolts, the positions of which are shown in Fig. 24.

[Illustration: FIG. 24.—Top of cycle shed. FIG. 25.—Floor of shed.]

The Floor (Fig. 25).—The making of this is so simple a matter that one need only point out the need for notching the end boards to allow the floor to touch the sides and back, and the doors when closed. It should be screwed to the frames, on which it rests, in a few places.

Preserving the Wood.—All outside wood is dressed with stoprot or creosote, rubbed well into the joints of the boarding.

Felting the Roof.—The felt is cut into 4-foot lengths, and each length has its ends turned over and nailed to the underside of the roof. The strips must overlap an inch or two. When the felt is on, dress it with boiled tar, and sprinkle sand over it while the tar is still liquid.

Fitting.—The two bolts to hold one door top and bottom and the lock are now fitted, and a couple of hooks screwed into the door frame clear of the door, to sling a machine from while it is being cleaned or adjusted.

Mounting the Shed.—The shed must be raised a few inches above the ground, on bricks or other suitable supports. Don’t stand it close to a wall. Air should be able to circulate freely under and all round it.

CUTTING DOWN EXPENSE.

If the cost appears prohibitive, it may be reduced somewhat (1) by using thinner boards; (2) by reducing the height of the shed by 1 foot. A very cheap shed, but of course not comparable in quality with the one described, can be made by using odd rough boards for the outside, and covering them with roofing felt well tarred.

VIII. A TARGET APPARATUS FOR RIFLE SHOOTING.

The base is a 1-inch board, 18 inches long and 7 inches wide.

The target-holder is a piece of wood 1-1/2 inches square, and a couple of inches longer than the side of the largest target to be used. To one face nail a piece of strip lead as weight; and to the parallel face attach, by means of brads driven in near one edge, a piece of thin wood of the same size as the face. The free long edge of this should be chamfered off slightly on the inside to enable the target to be slipped easily between it and the roller.

The roller is pivoted on two short spindles—which can be made out of stout wire nails—driven into the ends near the face farthest from the weight. (See Fig. 26.)

For standards use a couple of the small angle irons used for supporting shelves, and sold at about a penny each. These are screwed on to the board 2 inches from what may be considered to be the rear edge, and are so spaced as to leave room for a washer on each spindle between the roller and the standards, to diminish friction.

[Illustration: FIG. 26.-Side elevation of disappearing target apparatus.]

Remove one standard, and drive into the roller a piece of stout wire with its end bent to form an eye. The inclination of the arm to the roller is shown in Fig. 26.

To the front of the board now nail a rectangle of stout sheet iron, long and deep enough to just protect the standards and roller. Place the roller in position, insert a target, and revolve the roller to bring the target vertical. A small wire stop should now be fixed into the baseboard to prevent the arm coming farther forward, and a hole for the operating string be drilled in the protection plate at the elevation of the eye on the arm. The edges of this hole need careful smoothing off to prevent fraying of the string. A small eyelet or brass ring soldered into or round the hole will ensure immunity from chafing.

Drive a couple of long wire nails into the front edge of the board outside the iron screen to wind the string on when the target is put away.

It may prove a convenience if plain marks are made on the string at the distances from which shooting will be done.

The above description covers apparatus for working two or more targets simultaneously on a long roller, or separately on separate rollers mounted on a common baseboard.

If it is desired to combine with the apparatus a “stop” for the bullets, the latter (a sheet of stout iron of the requisite strength) may be affixed to the rear of the baseboard, and furnished with a handle at the top to facilitate transport.

IX. CABINET-MAKING.

A Match-box Cabinet.

This is useful for the storage of small articles, such as stamps, pens, seeds, needles, and a number of other minor things which easily go astray if put in a drawer with larger objects.

The best boxes for the purpose are those used for the larger Bryant and May matches. Select only those boxes of which the tray moves easily in the case.

The cases should be stood on end on some flat surface while being glued together. A box or drawer with truly square corners is useful for assembling them in; if they are packed into one corner they cannot slew about. Press the boxes together while the glue is setting.

Now glue the back ends of the cases (from which the trays should have been removed), and press them against a piece of thin card. When the glue is dry, apply some more with a small brush to the back angles inside the covers, to ensure a good hold on the backing. Trim off the card to the outline of the pile.

[Illustration: FIG. 27.—Match-box cabinet.]

Select for the front end of the drawer that for which the wood is doubled over. Paste outside the end a piece of white paper, whereon words and numbers will be more plainly visible. The life of the trays will be increased if the insides are neatly lined with thin paper.

For “handles” use boot buttons, or loops of thin brass wire, or brass paper clips. To give the cabinet a neat appearance you should cover it outside with paper of some neutral tint; and if you wish it to be stable and not upset when a rather sticky drawer is pulled out, glue it down to a solid wooden base of the proper size.

A Cardboard Cabinet.

We now proceed to a more ambitious undertaking—the manufacture of a cabinet for the storage of note-paper, envelopes, labels, etc. The only materials needed are some cardboard and glue; the tools, a ruler and a very sharp knife. For the marking out a drawing board and T-square are invaluable. The cardboard should be fairly stout, not less than 1/16 inch thick.

Begin with the drawers; it is easier to make the case fit the drawers than vice versa.

Mark out the drawers as shown in Fig. 28. The areas AA are the front and back; BB the sides. The dotted lines indicate the lines along which the cardboard is bent up. The sides are of exactly the same length as the bottom, but the front and back are longer than the bottom by twice the thickness of the cardboard, so as to overlap the sides. (The extra length is indicated by the heavy black lines.)

[Illustration: FIG. 28.—Drawer of cardboard cabinet marked ready for cutting.]

Measure and cut out very carefully to ensure all the drawers being of the same size. Lay a piece of card under the thing cut to avoid blunting the knife or damaging the table. When the blanks are ready, cut them almost through along the dotted lines. Use several strokes, and after each stroke test the stubbornness of the bend. When the card is almost severed it will bend up quite easily. Note.—Bend as shown in the inset C; not the other way, or you will snap the card. If you should be so unlucky as to cut the card through in places, paste a strip of thin paper along the line before turning up.

The four flaps are now bent up, glued together, and covered outside with paper. This part of the business is easy enough if a small square-cornered wooden box be used as a support inside at each angle in turn. It is advisable to glue strips along all the bends both inside and outside. The external strips should be flattened down well, so as to offer no loose edges.

Compare the drawers, and if one is slightly wider than the rest, use it to guide you in making the measurements for the case.

The sides and back of the case are cut out of a single piece. The sides should be a quarter of an inch deeper than the drawers to allow some overlap; the back slightly wider than the drawer.

As each drawer will be separated from that above it by a shelf, allowance must be made for the shelves, and also for a twentieth of an inch or so of “play” to each drawer. To keep on the safe side leave a little extra stuff to be removed later on.

Cut out the bottom to fit inside the back and sides exactly, and a sufficient number of shelves of precisely the same size as the bottom. Attach the bottom to the sides and back with internal and external strips. When the glue has set, place the guide drawer in position, and lay on it a piece of thin card to cover it over. This card is merely a removable “spacer.” Along the side and back edges of the shelf stick projecting strips of stout paper. When the adhesive is dry, turn the strips round the end at right angles to the division, glue them outside, and lay the division in position on top of the “spacer.”

Place the second drawer and shelf in like manner, and continue till the top of the cabinet is reached. Then mark off and cut away any superfluous card. Glue the top edges, and stand the cabinet head downwards on a piece of cardboard. Trim off the edges of this, and the top is completed, except for binding the corners.

Then attend to the outside back corners of the case, and paste strips in the angles under the shelves. The strips should be forced well into the angles.

For handles use brass rings let sufficiently far through the fronts of the drawers for a wedge of card to be slipped through them and stuck in position. The appearance of the cabinet will be enhanced by a neatly applied covering of paper.

A Cigar-box Cabinet.

At the rate of a halfpenny or less apiece one may buy the cigar boxes made to hold twenty-five cigars. These boxes, being fashioned by machinery, are all—at any rate all those devoted to a particular “brand”—of the same dimensions; they are neatly constructed, and their wood is well seasoned. Anyone who wishes to make a useful little cabinet may well employ the boxes as drawers in the said cabinet (Fig. 29).

Each box should be prepared as follows:-Remove the lid and paper lining, and rub all the paper binding off the outside angles with a piece of coarse glass paper. This is a safer method than soaking-off, which may cause warping and swelling of the wood. Then plane down the tops of the two sides till they are flush with the back and front, and glue into the corners small pieces of wood of right-angled-triangle section to hold the sides together and the bottom to the sides. To secure the parts further cut a number of large pins down to 3/4 inch, and drive these into the sides through holes carefully drilled in the bottom. Finally, rub the outside of the drawer well with fine glass paper or emery cloth till the surface is smooth all over.

The Case.—If mahogany can be obtained for this, so much the better, as the wood will match the boxes. In default of it, a white wood, stained, will have to serve.

[Illustration: FIG. 29.—Cabinet with cigar-box drawers.]

The two sides of the case should be prepared first Wood 3/8 inch thick is advised. Each side is 1 inch wider than the depth (outside) of a drawer from front to back. (Whether the drawers shall slide in lengthways or flatways is for the maker to decide.) The length of a side is calculated on the basis that the drawers will be separated from one another by runners 1/4 to 5/16 inch deep, and that a slight clearance must be allowed for the drawers to slide in and out freely. In the first instance cut the sides a bit too long. If it be preferred to insert the bottom between the sides, the length must be increased accordingly.

The runners are cut out of the box lids, and planed till their top and bottom edges are parallel. Their length is 1/4 inch less than the depth of a drawer. To fill up the spaces between the drawers in front you will need some slips of the same depth as the runners, and 3/8 inch longer than the drawer, so that they may be let 3/16 inch into the sides of the case at each end.

Affixing the Runners.—This is a very easy matter if a wooden spacer, slightly wider than the depth of the drawer, is prepared. Having decided which is to be the inside face and the forward edge of a side, lay the side flat, and apply the spacer with one edge flush with the bottom of the side, or as far away from it as the thickness of the bottom, as the case may be, and fix it lightly in position with a couple of tacks. The first runner is laid touching the spacer and a little back from the edge to give room for the cross-bar, and fastened by means of short tacks, for which holes had better be drilled in the runner to prevent splitting. The spacer is now transferred to the other side of the runner, and the second runner is fastened on above it; and so on till all the runners are in position. The square should be used occasionally to make sure that the tops of the runners are parallel to one another. The other side having been treated in like manner, any spare wood at the top is sawn off.

The notches for the front cross-bars between drawers are cut out with a very sharp narrow chisel.

The Top and Bottom.—Make the top of the same thickness as the sides; the bottom of somewhat stouter wood. If the bottom is cut a bit longer than the width of the case, and neatly bevelled off, it will help to smarten the appearance of the cabinet.

When fixing the sides to the bottom and top get the distance correct by placing the top and bottom drawers in position, and insert a piece of thin card between one end of the drawer and the side. This will ensure the necessary clearance being allowed for.

The Back.—Cut this out of thin wood. The top of a sweetstuff box-costing about a halfpenny—will do well enough. It should be quite rectangular and make a close fit, as it plays the important part of keeping the case square laterally. Bevel its back edges off a bit. Push it in against the back ends of the runners, and fix it by picture brads driven in behind.

The front bars should now be cut to a good fit and glued in the notches. This completes the construction.

Drop handles for the drawers may be made out of semicircles of brass wire with the ends turned up. The handles are held up to the drawer by loops of finer wire passed through the front and clinched inside.

The finishing of the outside must be left to the maker’s taste. Varnishing, or polishing with warmed beeswax, will add to the general appearance, and keep out damp.

The total cost of a ten-drawer cabinet ought not to exceed eighteen pence.

A Tool Cabinet.

The wooden cabinet shown in Fig. 30 is constructed, as regards its case, in the same way as that just described, but the drawers are built up of several pieces. The over-all dimensions of the cabinet represented are as follows: Height, including plinth, 25 inches; width, 17-3/8 inches; depth, 10-1/2 inches. The drawers are 16 inches wide (outside), by 10-1/8 inches from back to front, and, reckoning from the bottom upwards, are 3-1/4, 3, 2-1/2, 2, 2, 2, 2, and 1-3/4 inches deep.

[Illustration: FIG. 30.—Large cabinet (a), details of drawer joints (b, c, d), and padlock fastening (e).]

The construction of the drawers is indicated by the diagrams, Fig. 30, b, c, d. The fronts are of 5/8-inch, the sides and backs of 3/8-inch, and the bottoms of (barely) 1/4-inch wood. The grooves should not come nearer than 1/8-inch to the bottom edge, or be more than 5/16 inch wide and deep. The possessor of a suitable “plough” plane will have no difficulty in cutting them out; in the absence or such a tool the cutting gauge and chisel must be used.

The back piece of a drawer has 1/4-inch less height than the front, to allow the bottom to be introduced. The ends or the bottom are bevelled off towards the top edge to fit the grooves, so that no part may be above the grooves.

Glue should be used to attach the sides of a drawer to the back and front in the first place, and nails be added when the glue has set. As an aid to obtaining perfect squareness, without which the drawers will fit badly, it is advisable to mark out on a board a rectangle having the exact inside dimensions of a drawer, and to nail strips of wood up to the lines on the inside. If the parts are put together round this template they will necessarily fit squarely.

Divisions.—If the drawers are to be subdivided in one direction only, the partitions should run preferably from back to front, as this enables the contents of a compartment to be more easily seen. Where two-direction division is needed the partitions are cut as shown in Fig. 31. All partitions should touch the bottom, and be made immovable by gluing or nailing. It is a mistake to have so many divisions in a drawer that the fingers cannot get into them easily.

Wooden knobs for the drawers can be bought very cheaply of any turner, or suitable brass knobs at any ironmonger’s. Take care that the knobs are in line with one another; otherwise the general appearance of the cabinet will suffer.

[Illustration: FIG. 31.—Divisions of drawer notched to cross each other.]

Lock and Key.—If a cabinet is intended for storage of articles of any value it should be provided with lock and key. One lock will secure all the drawers if attached to a flap hinged on one side to the cabinet, as shown in Fig. 30 a, to engage a catch projecting from one of the drawers. A special form of lock is sold for the purpose. If the single flap seems to give a lop-sided effect, place a fellow on the other side, and fit it with sunk bolts to shoot into the overhanging top and plinth. If you wish to avoid the expense and trouble of fitting a lock, substitute a padlock and a staple clinched through the front of a drawer and passing through a slot in the flap (Fig. 30, e).

Alternative Method.—The fixing of the front bars can be avoided if the front of each drawer (except the lowest) be made to overhang the bottom by the depth of the runner. This method, of course, makes it impossible to stand a drawer level on a level surface.

X. TELEGRAPHIC APPARATUS.

The easily made but practical apparatus described in this chapter supplies an incentive for learning the Morse telegraphic code, which is used for sending sound signals, and for visible signals transmitted by means of flags, lamps, and heliograph mirrors. Signalling is so interesting, and on occasion can be so useful, that no apology is needed for introducing signalling apparatus into this book.

The apparatus in question is a double-instrument outfit, which enables an operator at either end of the line to cause a “buzzer” or “tapper” to work at the other end when he depresses a key and closes an electric circuit. Each unit consists of three main parts—(1) the transmitting key; (2) the receiving buzzer or tapper; (3) the electric battery.

The principles of an installation are shown in Fig. 33. One unit only is illustrated, but, as the other is an exact duplicate, the working of the system will be followed easily.

[Illustration: Fig. 32.—Morse alphabet]

A wooden lever, L, is pivoted on a support, A. Passing through it at the forward end is a metal bar having at the top a knob, K, which can be grasped conveniently in the fingers; at the other a brass screw, O, which is normally pulled down against the contact, N, by the spiral spring, S. The contact M under K is in connection with the binding post T1 and N with binding post T3; K is joined up to T2, and O to T4.

T3 and T4 are connected with one of the line wires; T1 with the other wire through a battery, B; T3 with the other wire through the buzzer, R. [1]

[Footnote 1: For the buzzer may be substituted the tapper, described on a later page.]

Assuming both keys to be at rest, as in Fig. 33, the two buzzers are evidently in circuit with the line wires, though no current is passing. If the stem of K is depressed to make contact with M, the electric circuit of which the battery, B, forms part is completed, and the buzzer at the other end of the lines comes into action. Since the depression of K raises O off N, the “home” buzzer’s connection with the line wires is broken, to prevent the current being short-circuited. The fact that this buzzer is periodically in circuit, even when the key is being worked, makes it possible for the operator at the other end to attract attention by depressing his key, if he cannot read the signals sent.

[Illustration: Fig.33—Telegraphic apparatus; sending key, buzzer and battery]

Making the Keys.

Transmitting keys can be bought cheaply, but not so cheaply as they can be made. The only expense entailed in home manufacture is that of the screw terminals for connecting the keys with the lines and buzzers. These cost only a penny each, and, if strict economy is the order of the day, can be dispensed with should the apparatus not have to be disconnected frequently.

The size of the key is immaterial. The keys made by me have levers 1 inch wide and 5-1/2 inches long, oak being chosen as material, on account of its toughness. K is in each case a small wooden knob on a piece of 3/16-inch brass rod; O a 1-1/2-inch brass screw; A a piece of sheet brass 3-1/2 inches long, marked off carefully, drilled 1/8 inch from the centre of each end for the pivot screws, and in four places for the holding-down screws, and bent up at the ends to form two standards. If you do not possess any brass strip, the lever may be supported on wooden uprights glued and screwed to the base.

[Illustration: Fig. 34—Telegraphic apparatus mounted on baseboard]

Contact M is a small piece of brass attached to the base by a screw at one end and by T1 at the other. K was drilled near the end to take the short coil of insulated wire joining it to T2, and O was similarly connected with T4.

The spring, S, should be fairly strong. A steel spiral with a loop at each end is most easily fitted. Drill holes in the lever and base large enough for the spring to pass through freely, make a small cross hole through the lever hole for a pin, and cut a slot across the base hole for a pin to hold the bottom of the spring. Adjust the lever by means of screw O so that there is a space of about 1/4-inch between K and M when O and N are in contact, and after the spring has been put in position give the screw a turn or two to bring K down to within 1/16 inch of M. This will put the required tension on the spring.

The Buzzers.—For these I selected a couple of small electric bells, costing 2s. 6d. each. Their normal rate of vibration being much too slow for telegraphic purposes, I cut off the hammers to reduce the inertia, and so adjusted the contact screw that the armature had to move less than one hundredth of an inch to break the circuit. This gave so high a rate of vibration that the key could not make and break the circuit quickly enough to prevent the buzzer sounding.

A Morse Tapper or Sounder.

In postal telegraph offices a “sounder,” and not a “buzzer,” is generally used to communicate the signals. Instead of a continuous noise, lasting as long as the key at the transmitting station is held down, the operator at the receiving station hears only a series of taps made by an instrument called a “sounder.” The principle of this simple device is illustrated by the working diagrams in Fig. 35. M is a horseshoe magnet fixed to a base, A. Close to it is an armature, AR, of soft iron, attached to a lever, L, which works on a pivot and is held up against a regulating screw, P1, by the pull of the spring SP. When current passes through the magnet the armature is attracted, and the point of the screw S2 strikes against P2; while the breaking of the circuit causes L to fly back against S1. The time intervening between the “down” and “up” clicks tells the operator whether a long or a short—dash or a dot—is being signalled.

[Illustration: FIG. 35.-Elevation and plan of telegraphic sounder.]

Materials.—A horseshoe magnet and armature taken from an electric bell provide the most essential parts of our home-made instrument in a cheap form. If these are available, expense will be limited to a few pence. Oak or walnut are the best woods to use for the lever, being more resonant than the softer woods, and for the standard B and stop V. Any common wood is good enough for the base A.

The lever L is 6 inches long, 1/2 inch deep, and 3/8-inch wide, and is pivoted at a point 4-1/4 inches from the stop end. The hole should be bored through it as squarely as possible, so that it may lie centrally without B being out of the square. A piece of metal is screwed to its top face under the adjusting screw S1.

The spring is attached to L and A in the manner already described on p. 89 in connection with the “buzzer.”

The plate P2 should be stout enough not to spring under the impact of the lever. Fig. 36 is an end view of the standard B. The drilling of the pivot hole through this requires care. The screw S2 should be so adjusted as to prevent the armature actually touching the cores of the magnets when attracted. The ends of the magnet winding wire, after being scraped, are clipped tightly against the base by the binding posts T1 T2.

If sounders are used in place of buzzers they are connected up with the keys, batteries, and line wires in the manner shown in Fig. 33.

Batteries.

The dry cells used for electric bells are the most convenient batteries to use. They can now be purchased at all prices from a shilling upwards, and give about 1-1/2 volts when in good condition. One cell at each end will suffice for short distances, or for considerable distances if large conductors are used. If a single cell fails to work the buzzer strongly through the circuit, another cell must be added.

[Illustration: FIG. 36.—Standard for sounder.]

For ease in transport it will be found advisable to mount key, buzzer, and battery on a common baseboard, which should be provided with a cover and handle. The three parts are interconnected with one another, and the line wire terminals as sketched in Fig. 34. This arrangement makes the apparatus very compact and self-contained. As a finishing touch fit the lid inside with clips for holding a stiff-backed writing pad and pencil for the recording of messages.

Lines.—Fencing made of stout galvanized iron wires strung on wooden posts supplies excellent conductors for practice purposes, provided the posts be quite dry. In wet weather there will be leakage. (Fencing with metal posts is, of course, unsuitable, as every post short-circuits the current.) The two wires selected for land lines must be scraped quite bright at the points where the connections are to be made.

It is an easy matter to rig up a telegraph line of galvanized wire 1/12 to 1/8 inch in diameter, strung along insulators (the necks of bottles serve the purpose excellently) supported on trees, posts, or rough poles. The length of the line will be limited by the battery power available, but a 6-volt battery at each end will probably suffice for all experimental purposes. A second wire is not needed if one terminal at each end is connected with a copper plate sunk in the ground, or with a metal fence, drain-pipe, etc.

XI. A RECIPROCATING ELECTRIC MOTOR.

The electric motor to be treated in this chapter illustrates very prettily the attractive force of a hollow, wire-wound bobbin on a movable core, when the electric current is passed through the wire. If one inserts the end of an iron rod into the coil, the coil exerts a pull upon it, and this pull will cease only when the centre of the rod is opposite the centre of the coil. This principle is used in the “electric gun,” which in its simplest form is merely a series of powerful coils arranged one behind another on a tube through which an iron or steel projectile can pass. The projectile closes automatically the circuit of each coil in turn just before reaching it, and breaks it before its centre is halfway through the coil, being thus passed along from one coil to the other with increasing velocity.

Our motor is essentially a very inefficient one, its energy being small for the current used, as compared with a revolving motor of the usual kind. But it has the advantage of being very easy to make.

[Illustration: FIG. 37.—Electric reciprocating engine and battery.]

How it works.—The experimental engine, constructed in less than a couple of hours, which appears in Fig. 38, consists of a coil, C, strapped down by a piece of tin to a wooden bedplate; a moving plunger, P, mounted on a knitting-needle slide rod, SR; a wire connecting rod, SR; a wooden crank, K; and a piece of knitting-needle for crank shaft, on which are mounted a small eccentric brass wipe, W, and a copper collar, D. Against D presses a brass brush, B1 connected with the binding post, T1; while under W is a long strip of springy brass against which W presses during part of every revolution. T2 is connected to one end of the coil winding, and T1 through a 4-volt accumulator or three dry cells, with the other end of the coil. When W touches B2 the circuit is completed, and the coil draws in the plunger, the contact being broken before the plunger gets home. The crank rotates at a very high speed if there is plenty of battery power, all the moving parts appearing mere blurs.

CONSTRUCTION.

The coil is made by winding 4 oz. of No. 32 cotton-covered wire (price 6d. to 8d.) on a boxwood reel 2 inches long and 1-1/2 inches in diameter, with a 9/16-inch central hole. Before winding, bore a hole for the wire through one end of the reel, near the central part, and mount the reel on a lathe or an improvised spindle provided with a handle of some kind. The wire should be uncoiled and wound on some circular object, to ensure its paying out regularly without kinking; which makes neat winding almost impossible.

Draw a foot of the wire through the hole in the reel, and drive in a tiny peg—which must not protrude inwards—to prevent it slipping. Lay the turns on carefully, forcing them into close contact, so that the next layer may have a level bed. On reaching the end of the layer, be equally careful to finish it neatly before starting back again. When the wire is all on, bore a hole as near the edge of the finishing edge as possible, and draw the spare wire through. Then cut a strip of tough paper of the width of the coils, coat one side with paste, and wrap it tightly round the outside to keep the wire in place.

Note.—Insulation will be improved if every layer of wire is painted over with shellac dissolved in alcohol before the next layer is applied.

Flatten the reel slightly with a file at the points of contact with the baseboard, to prevent rolling.

The plunger is a tube of thin iron, 1/16 inch less in diameter than the hole in the reel, and 1/4 inch longer than the reel. If a ready-made tube is not available, construct one by twisting a piece of tin round a metal rod, and soldering the joint. As it is difficult to make a jointed tube cylindrical, and a close fit is needed to give good results, it is worth going to a little trouble to get a plunger of the right kind.

The ends of the plunger are plugged with wood and bored centrally for the slide rod, which should not be cut to its final length until the parts are assembled.

The crank shaft is 2-3/4 inches of a stout knitting needle mounted in a sheet brass bearing. The crank, a fragment of oak or other tough wood, is balanced, and has a throw of 5/8 inch. The crank-shaft hole should be a trifle small, so that the crank shall get a tight hold of the shaft without pinning. The collar, D, and wipe, W, are soldered to the shaft after this has been passed through its bearings. The brush B1 should press firmly, but not unnecessarily so, against the collar. For B2 one must use very springy brass strip, a piece about 3 inches long and 1/4 inch wide being needed. Bend it to the arc of a large circle, and screw one end down to the base by the binding screw T2. The other end, which should not touch the base, is confined by the heads of a couple of small screws, by means of which the strip is adjusted relatively to the wipe.

Fixing the Coil.—Cut a strip of tin 1-3/4 inches wide and 4 inches long. Punch a couple of holes near one end, and nail this to the side of the base, with its forward end 4-1/4 inches from the crank shaft. Pass the strip over the coil, and bend it down towards the base. Drill a couple of screw holes, and screw the other end down so that the coil is gripped fairly tight.

Fixing the Plunger. Two small guides, G1 G2, are made for the plunger. The holes through which the slide rod moves should be a good fit, and their centres at the level of the centre of the coil. Screw holes are bored in the feet.

Pass the plunger through the coil, and place the guides on the rod. Then draw the plunger forward till 1/2 inch projects. Bring G1 close up to it, mark its position, and screw it to the base. The other guide, G2, should be 1-1/2 inches away from the rear of the coil.

[Illustration: Fig. 38.—Plan of electric reciprocating engine.]

The coil and guides must be adjusted so that the plunger does not touch the coil anywhere during a stroke, packings being placed, if necessary, under coil or guides. When the adjustment is satisfactory, screw the coil down tightly, and cut off any superfluous parts of the rod.

The Connecting Rod.—Bore a hole near the end of the plunger for a screw to hold the rear end of the connecting rod. Pull the plunger out till 1-3/4 inches project, turn the crank full forward, and measure off the distance between the centres of the plunger hole and the crank pin. Drive a couple of wire nails into a board, and twist the ends of a piece of 1/20-inch wire round them twice. This wire constitutes a connecting rod amply strong enough to stand the pulls to which it will be subjected. Fix the rod in position.

Adjusting the Wipe.—Turn the wipe, W, round until it makes contact with B2, and, holding the crank shaft with a pair of pliers, twist the crank on it till it just begins the return stroke. Then turn the crank to find out how long the wipe remains in contact, and adjust the crank relatively to the wipe so that the crank is vertical when the period of contact is half finished. The length of this period is controlled by the set screws at the free end of B2.

OTHER DETAILS.

The fly wheel may be a disc of wood.

Oil all the rubbing parts slightly. Connect T1 to one terminal of the battery, T2 to the coil, and the other terminal of the battery to the coil. Set the engine going. If it refuses to run, make sure that B1 is pressing against D. The speed of the engine may possibly be improved by careful adjustment of B2 and an alteration in the setting of the crank, and will certainly be accelerated by increasing the number of battery cells.

The cost of the engine described was about 1s, 3d., exclusive of the battery.

XII. AN ELECTRIC ALARM CLOCK.

Anybody who possesses an alarm clock with an external gong, an electric bell, and a battery, may easily make them combine to get the drowsiest of mortals out of bed on the chilliest of winter mornings. The arrangement has as its secondary advantages and capabilities—

(l) That the clock can be placed where its ticking will not disturb the person whom it has to arouse in due course (some of the cheaper clocks are very self-advertising);

(2) That one clock can be made to operate any number of bells in different parts of the house.

The main problem to be solved is, how to make the alarm mechanism of the clock complete an electric circuit when the alarm “goes off.”

If you examine an alarm clock of the type described, you will find that the gong hammer lies against the gong when at rest, and that its shaft when in motion vibrates to and fro about a quarter of an inch.

[Illustration: FIG. 89.—Plan of release gear of electric alarm, as attached to clock.]

Fig. 39 shows a. method of utilizing the movement of the hammer. A piece of wood, 2 inches long, wide enough to fill the space between the rear edge of the clock and the hammer slot, and 1/2 inch thick, has its under side hollowed out to the curvature of the clock barrel. This block serves as a base for two binding posts or terminals, T1 T2. A vertical slit is made in T1 and in this is soldered [to] one end of a little piece of spring brass strip, 1 inch long and 1/4 inch wide. To the back of the other end of the strip solder a piece of 1/20 inch wire, projecting l inch below the strip. The strip must be bent so that it presses naturally against T2. A little trigger, B, which you can cut out of sheet brass, is pivoted at a, where it must be raised off the base by a small washer. It projects 1/4 inch beyond the base on the gong support side. A square nick is cut in it at such a distance from a that, when the wire spike on C is in the nick, the strip is held clear of T2. The other end of the trigger, when the trigger is set, must be 1/8 inch from the shank of the alarm hammer—at any rate not so far away that the hammer, when it vibrates, cannot release C from the nick.

To fix the base on to the top of the clock, the works must be removed (quite an easy matter to accomplish) and holes bored for a couple of screws put through from the inside. If the underside of the base is not quite correctly curved, take care not to force in the screws far enough to distort the barrel. It is advisable to do the fitting of the parts of the release after the base has been fixed, and before the works are replaced. The position of the hammer shaft can be gauged accurately enough from the slot in the case.

The tails of the terminals T1 T2 must be truncated sufficiently not to penetrate the base and make contact with the barrel, or a “short circuit” will be evident as soon as the battery is connected up.

[Illustration: Fig. 40.—Electric alarm releaser, as attached to separate wooden clock casing.]

If the bell, battery, and clock are in the same room, a single dry cell will give sufficient current; but if the circuit is a long one, or several bells have to be operated, two or more cells will be required.

An Alternative Arrangement.—Should the reader prefer to have the clock quite free from the release—and this is certainly convenient for winding and setting the alarm—he should make a little wooden case for the clock to stand in, just wide enough to take the clock, and the back just as high as the top of the barrel. The release is then attached to a little platform projecting from the back, care being taken that the lever is arranged in the correct position relatively to the hammer when the clock is pushed back as far as it will go (Fig. 40).

If a self-contained outfit is desired, make the case two-storied: the upper division for the clock, the lower for the cell or cells. The bell may be attached to the front. A hinged fretwork front to the clock chamber, with an opening the size of the face; a door at the back of the cell chamber; and a general neat finish, staining and polishing, are refinements that some readers may like to undertake.

Setting the Alarm.—A good many alarm clocks are not to be relied upon to act within a quarter of an hour or so of the time to which they are set. But absolute accuracy of working may be obtained if the clock hands are first set to the desired hour, and the alarm dial hand revolved slowly till the alarm is released. The hands are then set at the correct time, and the alarm fully wound.

XIII. A MODEL ELECTRIC RAILWAY.

The rapid increase in the number of electrically worked railways, and the substitution of the electric for the steam locomotive on many lines, give legitimate cause for wondering whether, twenty or so years hence, the descendants of the “Rocket” will not have disappeared from all the railways of the world, excepting perhaps those of transcontinental character.

[Illustration: Fig. 41.—Electric Locomotive.]

The change is already spreading to model plant, and not without good reason, as the miniature electric railway possesses decided advantages of its own. Instead of having to chase the locomotive to stop or reverse it, one merely has to press a button or move a switch. The fascinations of a model steam locomotive, with its furnace, hissing of steam, business-like puffings, and a visible working of piston and connecting rods, are not to be denied, any more than that a full-sized steam locomotive is a more imposing object at rest or in motion than its electric rival. On the other hand, the ease of control already noticed, and the absence of burning fuel, water leakage, smoke and fumes, are strong points in favour of the electric track, which does no more harm to a carpet than to a front lawn, being essentially clean to handle. Under the head of cost the electric locomotive comes out well, as motors can be purchased cheaply; and connecting them up with driving wheels is a much less troublesome business than the construction of an equally efficient steamer. One may add that the electric motor is ready to start at a moment’s notice: there is no delay corresponding to that caused by the raising of steam.

The Track

We will consider this first, as its design must govern, within certain limits, the design of the locomotive. There are three systems of electrical transmission available.

1. The trolley system, with overhead cable attached to insulators on posts, to carry the current one way, the rails being used as the “return.” This system has the disadvantages associated with a wire over which the human foot may easily trip with disastrous effect.

2. That in which one of the wheel rails is used for taking the current to the motor, and the other as the return. The objection to the system is that the wheels must be insulated, to prevent short circuiting; and this, besides causing trouble in construction, makes it impossible to use the ordinary model rolling stock. To its credit one may place the fact that only two rails are needed.

3. The third and, we think, best system, which has an insulated third rail as one half of the circuit, and both wheel rails as the return, the motor being kept in connection with the third rail by means of a collector projecting from the frame and pressing against the top of the third rail. The last, for reasons of convenience, is placed between the wheel rails. We will assume that this system is to be employed.

[Illustration: FIG. 42.—Details of rails for electric track.]

Gauge.—For indoor and short tracks generally it is advisable to keep the gauge narrow, so that sharp curves may be employed without causing undue friction between rails and wheels. In the present instance we specify a 2-inch gauge, for which, as also for 1-1/2 and 1-1/4 inch, standard rolling stock is supplied by the manufacturers.

Track Construction.—It is essential that the centre rail and at least one of the wheel rails shall have all joints bonded together to give a clear course to the electric current, and the centre rail must be insulated to prevent leakage and short-circuiting. Where a track is laid down more or less permanently, the bonding is most positively effected by means of little fish-plates, screwed into the sides of the abutting rails; but in the case of a track which must be capable of quick coupling-up and uncoupling, some such arrangement as that shown in Fig. 42 is to be recommended.

Fig. 42 (a) is a cross vertical section of the track; Fig. 42 (c) a longitudinal view; while Fig. 42 (b) shows in plan a point of junction of two lengths of rail.

The wheel rails are made of carefully straightened brass strip 3/8 inch wide and 1/16 inch thick, sunk rather more than 1/8 inch into wooden sleepers (Fig. 42, a), 3-1/2 inches long and 3/4 inch wide (except at junctions). The sleepers are prepared most quickly by cutting out a strip of wood 3-1/2 inches wide in the direction of the grain, and long enough to make half a dozen sleepers. Two saw cuts are sunk into the top, 2 inches apart, reckoning from the inside edges, to the proper depth, and the wood is then subdivided along the grain. The saw used should make a cut slightly narrower than the strip, to give the wood a good hold. If the cut is unavoidably too large, packings of tin strip must be forced in with the rail on the outside. To secure the rails further, holes are bored in them on each side of the sleeper (see Fig. 42, c), and fine iron or, brass wire is passed through these, round the bottom of the sleeper, and made fast.

[Illustration: FIG. 43.—Tin chair for centre rail of electric track.]

The centre rail is soldered to small tin chairs, the feet of which are pinned down to the sleepers. The top of the rails must project slightly above the chairs, so that the current collector may not be fouled.

Junctions.—At these points one 3/4-inch sleeper is reduced to 1/2-inch width, and the other increased to 1 inch, this sleeper being overlapped 3/8 inch by the rails of the other section. To the outsides of the wheel rails are soldered the little angle plates, AA, BB, attached to the sleepers by brass tacks, which project sufficiently to take the brass wire hooks. These hooks must be of the right length to pull upon the tacks in AA and make a good contact. The centre rails are bonded by two strips of springy brass, riveted to one section, and forced apart at their free end by the interposed strip. Two pins projecting from the narrower sleeper fit into holes in the wider to keep the sections in line at a junction.

General.—The sleepers of straight sections are screwed down to 3/4 by 1/4 inch longitudinals, which help to keep the track straight and prevent the sleepers slipping. Sections should be of the same length and be interchangeable. Make straight sections of the greatest convenient length, to reduce the number of junctions. Sleepers need not be less than 6 inches apart. Fix the sleepers on the longitudinals before hammering the rails into the slots.

[Illustration: FIG. 44.—Laying out a curve for electric track.]

Curves.—A simple method of laying out a semi-circular curve is shown in Fig. 44. Sleepers and longitudinals are replaced by 1/2-inch boards, 8 inches wide. Three pieces, about 32 inches long each, have their ends bevelled off at an angle of 60 degrees, and are laid with their ends touching. Two semi-circles of 24 and 22 inch radius are drawn on the boards to indicate the positions of the rails, and short decapitated brass nails are driven in on each side of a rail, about an inch apart, as it is laid along one of these lines. (See Fig. 44. A.) The inside nails must not project sufficiently to catch the wheel flanges. The spring of the brass will prevent the rail falling out of place, but to make sure, it should be tied in with wire at a few points. The centre rail should on the curves also be 3/8 inch deep, and raised slightly above the bed so as to project above the wheel rails. The method already described of bonding at joints will serve equally well on curves. If the outer rail is super-elevated slightly, there will be less tendency for the rolling stock to jump the track when rounding the curve.

When the rails are in place the boards may be cut with a pad-saw to curves corresponding with the breadth of the track on the straight. If the boards incline to warp, screw some pieces of 1/8-inch strip iron to the under side across the grain, sinking the iron in flush with the wood.

The brass strip for the rails costs about one penny per foot run. Iron strip is much cheaper, but if it rusts, as it is very likely to do, the contact places will need constant brightening.

Points.—Fig. 45 shows the manner of laying out a set of points, and connecting up the rails. The outside wheel rails, it will be seen, are continuous, and switching is effected by altering the position of the moving tongues, pivoted at PP, by means of the rod R, which passes through a hole in the continuous rail to a lever or motor of the same reversible type as is used for the locomotive. If a motor is employed, R should be joined to a crank pin on the large driven cog—corresponding to that affixed to the driving wheel (Fig. 47)—by a short rod. The pin is situated at such a distance from the axle of the cog wheel that a quarter of a revolution suffices to move the points over. The points motor must, of course, have its separate connections with the “central station.” To show how the points lie, the rod R also operates a semaphore with a double arm (Fig. 46), one end of which is depressed—indicating that the track on that side is open—when the other is horizontal, indicating “blocked.” The arms point across the track.

[Illustration: FIG. 45.—Points for electric railway.]

Details.—The tongues must be bevelled off to a point on the sides respectively nearest to the continuous rails. The parts AA are bent out at the ends to make guides, which, in combination with the safety rails, will prevent the wheels jumping the track. Care should be taken to insulate centre rail connecting wires where they pass through or under the wheel rails.

It is advisable to lay out a set of points, together with motor and signals, on a separate board.

[Illustration: Fig. 46.—Double-armed signal, operated by points.]

Preservation of Track.—All the wooden parts of an outdoor track should be well creosoted before use.

The Electric Locomotive.

An elevation and a plan of this are given in Fig. 47. The two pairs of wheels are set close together, so that they may pass easily round curves.

[Illustration: Fig. 47.—Plan and elevation of electric locomotive.]

The Motor.—A motor of ordinary type, with electro field magnets, is unsuitable for traction, as it cannot be reversed by changing the direction of the current, unless a special and rather expensive type of automatic switch be used. While a motor of this kind is, in conjunction with such a switch, the most efficient, the motor with permanent field magnets is preferable as regards cost and ease of fixing. It can be reversed through the rails. The armature or revolving part must be tripolar to be self-starting in all positions.

A motor of sufficient power can be bought for half a crown or less—in any case more cheaply than it can be made by the average amateur.

The motor used for the locomotive illustrated was taken to pieces, and the magnet M screwed to a strip of wood 1-5/8 inches wide; and for the original armature bearings were substituted a couple of pieces of brass strip, HH, screwed to two wooden supports, SS, on the base, E (Fig. 47, a). It was found necessary to push the armature along the spindle close to the commutator piece, C, and to shorten the spindle at the armature end and turn it down to the size of the original bearing, in order to bring the motor within the space between the wheels.

The place of the small pulley was taken by an 8-toothed pinion wheel, engaging with a pinion soldered to the near driving wheel, the diameter of which it exceeded by about 3/16 inch. The pair, originally parts of an old clock purchased for a few pence, gave a gearing-down of about 9 times.

The position of the driven wheels relatively to the armature must be found experimentally. There is plenty of scope for adjustment, as the wheels can be shifted in either direction longitudinally, while the distance between wheel and armature centres may be further modified in the length of the bearings, BE. These last are pieces of brass strip turned up at the ends, and bored for axles, and screwed to the under side of the base. To prevent the axles sliding sideways and the wheels rubbing the frame, solder small collars to them in contact with the inner side of the bearings.

The Frame.—Having got the motor wheels adjusted, shorten E so that it projects 2 inches beyond the centres of the axles at each end. Two cross bars, GG, 3-1/2 inches long, are then glued to the under side of E, projecting 1/8 inch. To these are glued two 3/8-inch strips, FF, of the same length as E. A buffer beam, K, is screwed to G. A removable cover, abedfg, is made out of cigar-box wood or tin. The ends rest on GG; the sides on FF. Doors and windows are cut out, and handrails, etc., added to make the locomotive suggest the real thing—except for the proportionate size and arrangement of the wheels.

Electrical Connections.—The current collector, CR, should be well turned up at the end, so as not to catch on the centre rail joints, and not press hard enough on the rail to cause noticeable resistance. The fixed end of CR is connected through T2 with one brush, B, and both wheel bearings with T1.

[Illustration: FIG. 48.—Reversing switch.]

Electrical Fittings.—The best source of power to use is dry cells giving 1-1/2 to 2 volts each. These can be bought at 1s. apiece in fairly large sizes. Four or five connected in series will work quite a long line if the contacts are in good condition.

A reversing switch is needed to alter the direction of the current flow. The construction of one is an exceedingly simple matter. Fig. 48 gives a plan of switch and connection, from which the principle of the apparatus will be gathered. The two links, LL, are thin springy brass strips slightly curved, and at the rear end pivoted on the binding posts T1 T2. Underneath the other ends solder the heads of a couple of brass nails. The links are held parallel to one another by a wooden yoke, from the centre of which projects a handle. The three contacts C1 C2 C3 must be the same distance apart as the centres of the link heads, and so situated as to lie on the arcs of circles described by the links. The binding post T3 is connected with the two outside contacts—which may be flat-headed brass nails driven in almost flush with the top of the wooden base—by wires lying in grooves under the base, and T4 with the central contact. As shown, the switch is in the neutral position and the circuit broken.

[Illustration: Fig. 49.—Multiple battery switch.]

Multiple Battery Switch.—To control the speed of the train and economize current a multiple battery switch is useful. Fig. 49 explains how to make and connect up such a switch. The contacts, C1 to C5, lie in the path of the switch lever, and are connected through binding posts T1 to T6 with one terminal of their respective cells. The cells are coupled up in series to one another, and one terminal of the series with binding posts T0 and T6. By moving the lever, any number of the cells can be put in circuit with T7. The button under the head of the lever should not be wide enough to bridge the space between any two contacts. Change the order of the cells occasionally to equalize the exhaustion.

[Illustration: FIG. 50.—Adjustable resistance for controlling current.]

Resistance.—With accumulators, a “resistance” should be included in the circuit to regulate the flow of current. The resistance shown in Fig. 50 consists of a spiral of fine German silver wire lying in the grooved circumference of a wood disc. One of the binding posts is in connection with the regulating lever pivot, the other with one end of the coil. By moving the lever along the coil the amount of German silver wire, which offers resistance to the current, is altered. When starting the motor use as little current as possible, and open the resistance as it gets up speed, choking down again when the necessary speed is attained.

General.—All the three fittings described should for convenience be mounted on the same board, which itself may form the cover of the box holding the dry cells or accumulators.

SOME SUGGESTIONS.

Instead of dry cells or accumulators a small foot or hand operated dynamo generating direct, not alternating current, might be used. Its life is indefinitely long, whereas dry cells become exhausted with use, and accumulators need recharging from time to time. On occasion such a dynamo might prove very convenient.

Anyone who possesses a fair-sized stationary engine and boiler might increase the realism of the outdoor track by setting up a generating station, which will give a good deal of extra fun.

XIV. A SIMPLE RECIPROCATING ENGINE.

Figs. 51 and 52 illustrate a very simple form of fixed-cylinder engine controlled by a slide valve.

An open-ended “trunk” piston, similar in principle to that used in gas engines, is employed; and the valve is of the piston type, which is less complicated than the box form of valve, though less easily made steam-tight in small sizes. The engine is single-acting, making only one power stroke per revolution.

The cylinder is a piece of brass tubing; the piston another piece of tubing, fitting the first telescopically. Provided that the fit is true enough to prevent the escape of steam, while not so close as to set up excessive friction, a packing behind the piston is not needed; but should serious leakage be anticipated, a packing of thick felt or cloth, held up by a washer and nuts on the gudgeon G, will make things secure. Similarly for the built-up piston valve P may be substituted a piece of close-fitting brass rod with diameter reduced, except at the ends, by filing or turning, to allow the passage of steam.

CONSTRUCTION.

[Illustration: FIG. 51.—Elevation of simple reciprocating steam engine.]

The bed is made of wood, preferably oak, into the parts of which linseed oil is well rubbed before they are screwed together, to prevent the entry of water. A longitudinal groove is sawn in the top of the bed, as indicated by the dotted line in Fig. 51, to give room for the connecting rod in its lowest position, and a cross groove is scooped in line with the crank shaft to accommodate the lower part of the crank disc and the big end of the rod. (If the wing W under the cylinder is screwed to the side of the bed, instead of passing through it, as shown, a slight cutting away of the edge will give the necessary clearance in both cases. )

[Illustration: FIG. 52.—Plan of simple reciprocating steam engine.]

The cylinder and valve tube A should be flattened by filing and rubbing on emery cloth, so that they may bed snugly against one another and give a good holding surface for the solder. A steam port, S P, should next be bored in each, and the “burr” of the edges cleaned off carefully so as not to obstruct valve or piston in the slightest degree. “Tin” the contact surfaces thinly, and after laying valve tube and cylinder in line, with the portholes corresponding exactly, bind them tightly together with a turn or two of wire, or hold them lightly in a vice, while the solder is made to run again with the aid of a spirit lamp. If it seems necessary, run a little extra solder along the joint, both sides, and at the ends.

The valve, if built up, consists of a central rod, threaded at the rear end, four washers which fit the tube, and a central spacing-piece. The forward washer is soldered to the rod. Behind this is placed a felt packing. Then come in order the central spacing-piece, with a washer soldered to each end, a second packing, and a fourth washer. The series is completed by an adjusting nut to squeeze the packings, and a lock nut to prevent slipping. The back end of the valve must be wide enough to just more than cover the steam port. If the felt proves difficult to procure or fit, one may use a ring or two of brass tubing, with an external packing of asbestos cord.

The cylinder wing W should have the top edge turned over for an eighth of an inch or so to give a good bearing against the cylinder, and be held in position by a wire while the soldering is done. It is important that the line of the wing should be at right angles to a line passing through the centres of the valve tube and cylinder.

Shaft Bearings.—Take a piece of strip brass half an inch or so wide and 3-1/2 inches long. Bore four holes for screws, and scratch cross lines an inch from each extremity. Turn up the ends at these lines at right angles to the central part, stand the piece on some flat surface, and on the outer faces of the uprights scratch two cross lines at the height of the centre of the cylinder above the bed. Mark the central points of these lines.

Next select a piece of brass tubing which fits the rod chosen for the crank shaft, and bore in the bearing standards two holes to fit this tubing. Slip the tubing through the standards and solder it to them. The ends and central parts of the tubing must now be so cut away as to leave two bearings, BB—that at the fly-wheel end projecting far enough to allow the fly wheel, when brought up against it, to just clear the bed; that at the crank end being of the proper length to allow the eccentric to be in line with the valve rod, and the crank disc to occupy its proper position relatively to the central line of the cylinder. Finish off the standards by filing the tops concentrically with the bearings.

The eccentric may be built up from a metal disc about 3/4 inch diameter and two slightly larger discs soldered concentrically to the sides. The width of the middle disc should be the same as that of the eccentric rod. A careful filer could make a passable eccentric by sinking a square or semicircular groove in the edge of a wide disc. The centre of the eccentric must be found carefully, and a point marked at a distance from it equal to half the travel of the valve. To ascertain this, pull the valve forward until the steam port is fully exposed, insert a bar at the rear end of the valve tube, and mark it. Then push the valve back until a wire pushed through the port from the cylinder side shows that the port is again fully exposed. Insert and mark the bar again. The distance between the marks gives you the “travel” required.

Order of Assembly.—The following list of operations in their order may assist the beginner:

Make the bed.

Cut out cylinder barrel, piston, and valve tube.

Bevel off the ends of the last inside to allow the valve to enter easily.

Make the valve.

Bore the steam ports, and solder valve tube and cylinder together.

Solder holding-down wing, W, to cylinder.

Finish off the piston.

Solder the bearings in their standards.

Prepare shaft, crank disc, crank pin, and piston rod.

Fix the cylinder to the bed, in which a slot must be cut for the wing and holding-down bolt.

Attach the piston rod to the piston, and insert piston in cylinder.

Bore hole for shaft in centre of crank disc, and another, 9/16 inch away (centre to centre), for crank pin.

Solder in crank pin squarely to disc.

Pass shaft through bearings and slip on the crank disc.

Pass front end of piston rod over the crank pin.

Lay bearing standard on bed squarely to the centre line of the cylinder, turn crank fully back, and move the standard about till the back end of the piston clears the back end of the cylinder by about 1/32 inch.

Get standard quite square, and adjust sideways till connecting rod is in line with axis of cylinder.

Mark off and screw down the standard.

Make the eccentric, eccentric rod, and strap. Slip eccentric on shaft.

Put valve in position and draw it forward till the port is exposed.

Turn the eccentric forward, and mark the rod opposite centre of valve pin.

Bore hole for pin, and insert pin.

Hold the crank shaft firmly, and revolve eccentric till the port just begins to open on its forward stroke. Rotate crank disc on shaft till the crank pin is full forward.

Solder eccentric and disc to shaft.

Solder steam pipe to cylinder, and a brass disc to the rear end of the cylinder.

Fit a fly wheel of metal or wood. This must be fairly heavy, as it has to overcome all friction during the return or exhaust stroke.

## Action of Engine.—During the forward motion of the piston the valve is

pushed back by the eccentric until the steam port is fully opened, and is then drawn forward, covering the port. At the end of the power stroke the port has begun to open to the air, to allow the steam to escape throughout the exhaust stroke, in the course of which the valve is pushed back until, just at the end of the stroke, the steam port begins to open again.

Notes.— (l.) The connecting rod may be made shorter than shown in Figs. 51 and 52; but in that case the piston also must be shortened to allow for the greater obliquity of the rod at half-stroke.

(2.) If two opposed cylinders are made to operate the one crank, a double-acting engine is obtained. Both valves may be operated by a single eccentric, the connecting rod of one being pivoted to a small lug projecting from the eccentric strap. If three cylinders are set 120 degrees apart round the crank shaft, a continuous turning effect is given. This type will be found useful for running small dynamos.

(3.) If it is desired to use the exhaust steam to promote a draught in the boiler furnace, it should be led away by a small pipe from the rear end of the valve tube.

XV. A HORIZONTAL SLIDE-VALVE ENGINE.

The reader who has succeeded in putting together the simple engine described in the preceding chapter may wish to try his hand on something more ambitious in the same line. The engine illustrated in Figs. 53 to 66 will give sufficient scope for energy and handiness with drill and soldering iron. The writer made an engine of the same kind, differing only from that shown in the design of the crosshead guides, without the assistance of a lathe, except for turning the piston and fly wheel—the last bought in the rough. Files, drills, taps, a hack saw, and a soldering iron did all the rest of the work.

Solder plays so important a part in the assembling of the many pieces of the engine that, if the machine fell into the fire, a rapid disintegration would follow. But in actual use the engine has proved very satisfactory; and if not such as the highly-skilled model-maker with a well-equipped workshop at his command would prefer to expend his time on, it will afford a useful lesson in the use of the simpler tools. Under 50 lbs. of steam it develops sufficient power to run a small electric-lighting installation, or to do other useful work on a moderate scale.

[Illustration: Fig. 53.—Elevation of a large horizontal engine.]

The principal dimensions of the engine are as follows:

Bedplate (sheet zinc), 13-1/2 inches long; 4-1/2 inches wide; 1/8 inch thick.

Support of bedplate (1/20 inch zinc), 3 inches high from wooden base to underside of bedplate.

Cylinder (mandrel-drawn brass tubing), 1-1/2 inches internal diameter; 2-13/16 inches long over all.

Piston, 1-1/2 inches diameter; 1/2 inch long.

Stroke of piston, 2-1/4 inches.

Connecting rod, 5 inches long between centres; 5/16 inch diameter.

Piston rod, 5-1/8 inches long; 1/4 inch diameter.

Valve rod, 4-1/8 inches long; 3/16 inch diameter.

Crank shaft, 5 inches long; 1/2 inch diameter.

Centre line of piston rod, 1-1/4 inches laterally from near edge of bed; 1-5/8 inches from valve-rod centre line; 1-5/8 inches vertically above bed.

Centre line of crank shaft, 10-3/8 inches from cross centre line of cylinder.

Bearings, 1 inch long.

Eccentric, 9/32-inch throw.

Fly wheel, diameter, 7-1/2 inches; width, 1 inch; weight, 6 lbs.

Pump, 3/8-inch bore; 3/8-inch stroke; plunger, 2 inches long.

[Illustration: Fig. 54.—Plan of a large horizontal engine.]

Other dimensions will be gathered from the various diagrams of details.

The reader will, of course, suit his own fancy in following these dimensions, or in working to them on a reduced scale, or in modifying details where he considers he can effect his object in a simpler manner.

The diagrams are sufficiently explicit to render it unnecessary to describe the making of the engine from start to finish, so remarks will be limited to those points which require most careful construction and adjustment.

[Illustration: Fig. 55.—Standards of Bedplate.]

The Bedplate.—This should be accurately squared and mounted on its four arch-like supports. (For dimensions, consult Fig. 55.) Half an inch is allowed top and bottom for the turnovers by which the supports are screwed to the bedplate and base. The ends of the longer supports are turned back so as to lie in front of the end supports, to which they may be attached by screws or solder, after all four parts have been screwed to the bed. Care must be taken that the parts all have the same height. Drill all holes in the turnovers before bending. Use 1/8-inch screws. Turn the bed bottom upwards, and stand the four supports, temporarily assembled, on it upside down and in their correct positions, and mark off for the 3/32-inch holes to be drilled in the bed. A hole 3/4 inch in diameter should be cut in the bedplate for the exhaust pipe, round a centre 2 inches from the end and 1-5/8 inches from the edge on the fly-wheel side, and two more holes for the pump.

Making the Cylinder Slide and Valve.—The cylinder barrel must be perfectly cylindrical and free from any dents. Mandrel-drawn brass tubing, 1/16-inch thick, may be selected. If you cannot get this turned off at the ends in a lathe, mark the lines round it for working to with the aid of a perfectly straight edged strip of paper, 2-13/16 inches wide, rolled twice round the tube. The coils must lie exactly under one another. Make plain scratches at each end of the paper with a sharp steel point. Cut off at a distance of 1/16-inch from the lines, and work up to the lines with a file, finishing by rubbing the ends on a piece of emery cloth resting on a hard, true surface.

[Illustration: FIG. 56.-Cylinder standard before being bent.]

A square-cornered notch 1/8 inch deep and 7/8 inch wide must now be cut in each end of the barrel, the two notches being exactly in line with one another. These are to admit steam from the steam ways into the cylinder.

Cylinder Standards.-Use 5/64 or 3/32 inch brass plate for these. Two pieces of the dimensions shown in Fig. 56 are needed. Scratch a line exactly down the middle of each, and a cross line 1/2 inch from one end. The other end should be marked, cut, and filed to a semicircle. Drill three 3/16-inch holes in the turnover for the holding-down screws. The two standards should now be soldered temporarily together at the round ends and trued up to match each other exactly. Place them in the vice with the bending lines exactly level with the jaws, split the turnovers apart, and hammer them over at right angles to the main parts. Whether this has been done correctly may be tested by placing the standards on a flat surface. Take the standards apart, and scratch a cross line on each 1-5/8 inch from the lower surface of the foot on the side away from the foot. Make a punch mark where the line crosses the vertical line previously drawn, and with this as centre describe a circle of the diameter of the outside of the barrel. Cut out the inside and file carefully up to the circle, stopping when the barrel makes a tight fit. On the inside of the hole file a nick 1/8 inch deep, as shown in Fig. 56. Remember that this nick must be on the left of one standard and on the right of the other, so that they shall pair off properly.

Standards and barrel must now be cleaned for soldering. Screw one standard down to a wood base; slip one end of the barrel into it; pass the other standard over the other end of the barrel, and adjust everything so that the barrel ends are flush with the, outer surfaces of the standard, and the nicks of the barrel in line with the standard nicks. Then screw the other standard to the base. Solder must be run well into the joints, as these will have to stand all the longitudinal working strain.

The next step is the fitting of the cylinder covers. If you can obtain two stout brass discs 2-1/8 inches in diameter, some trouble will be saved; otherwise you must cut them out of 3/32-inch plate. The centre of each should be marked, and four lines 45 degrees apart be scratched through it from side to side. A circle of 15/16-inch radius is now drawn to cut the lines, and punch marks are made at the eight points of intersection. Solder the covers lightly to the foot side of their standards, marked sides outwards, and drill 1/8-inch holes through cover and standard at the punch marks. Make matching marks on the edges. Unsolder the covers, enlarge the holes in them to take 5/32-inch screws; and tap the holes in the standards. This method will ensure the holes being in line, besides avoiding the trouble of marking off the standards separately.

Bore a 1/4-inch hole in the centre of one cover—be sure that it is the right one—for the piston rod.

You can now proceed to the making of the piston-rod gland (Fig. 54, G1). Fig. 57 shows how this is built up of pieces of tubing and brass lugs for the screws. If possible, get the tubular parts trued in a lathe.

[Illustration: FIG. 57.—Vertical section of cylinder.]

Before the gland is soldered to the cover, the cover should be put in place, the piston rod attached to the piston, and the parts of the gland assembled. Push the piston rod through the cover until the piston is hard up against the back of the cover. Slip the gland over the rod, turn it so that the screws are parallel to the foot of the standard, and make the solder joint. This is the best way of getting the gland exactly concentric with the cylinder so that the piston rod shall move without undue friction. But you must be careful not to unsolder the cylinder from its standard or the parts of the gland. Blacken the piston rod in a candle flame to prevent solder adhering.

Steam Chest.—The walls of the steam chest are best made in one piece out of 1/2-inch brass by cutting out to the dimension given in Fig. 58. A sharp fret saw will remove the inside rectangle. Get both inside and outside surfaces as square as possible in all directions, and rub down the two contact faces on emery cloth supported by an old looking-glass.

[Illustration: FIG. 68.-Wall-piece for steam chest, with gland and valve rod in position.]

Two perfectly flat plates of 1/8-inch brass are cut to the size given in Fig. 59, or a little longer both ways, to allow for working down to the same area as the wall-piece. This operation should be carried out after soldering the three pieces together. File and rub the sides until no projections are visible. Then drill twelve 3/32-inch holes right through the three parts. After separating them, the holes in the walls and what will be the cover must be enlarged to an easy fit for 1/8-inch bolts, and the valve plate tapped.

Now drill 3/16-inch holes centrally through the ends of the walls for the valve rod. If the first hole is drilled accurately, the second hole should be made without removing the drill, as this will ensure the two holes being in line. If, however, luck is against you, enlarge the holes and get the rod into its correct position by screwing and soldering small drilled plates to the outside of the chest. Also drill and tap a hole for the lubricator. The attachment of the gland (Fig. 54, G2) is similar to that of the cylinder gland, and therefore need not be detailed.

The Valve Plate (Fig. 59).—Three ports must be cut in this—a central one, 7/8 by 3/32 inch, for the exhaust; and two inlets, 7/8 by 3/32 inch, 1/8 inch away from the exhaust. These are easily opened out if a series of holes be drilled along their axes.

[Illustration: FIG. 69.—Valve plate.]

The Steam Ways.—The formation of the steam ways between valve plate and cylinder is the most ticklish bit of work to be done on the engine as it entails the making of a number of solder joints close together.

[Illustration: FIG. 60.—Piece for steam ways.]

We begin by cutting out of 1/20-inch sheet brass a piece shaped as in Fig. 60. Parallel to the long edges, and 3/8 inch away, scribe bending lines. Join these by lines 5/8 inch from the short edges, and join these again by lines 1/4 inch from the bending lines. Cuts must now be made along the lines shown double in Fig. 60. Bend parts CC down and parts BB upwards, so that they are at right angles to parts AA. The positions of these parts, when the piece is applied to the cylinder, are shown in Fig. 62.

[Illustration: FIG. 61.—Valve plate and steam ways in section.]

One must now make the bridge pieces (Fig. 61, a, a) to separate the inlet passages from the exhaust. Their width is the distance between the bent-down pieces CC of Fig. 60, and their bottom edges are shaped to the curvature of the cylinder barrel. Finally, make the pieces bb (Fig. 61), which form part of the top of the steam ways.

In the assembling of these parts a blowpipe spirit lamp or a little “Tinol” soldering lamp will prove very helpful.

The following order should be observed:

(1.) Solder the piece shown in Fig. 60 to the cylinder barrel by the long edges, and to the cylinder supports at the ends. This piece must, of course, cover the steam ports in the cylinder.

(2.) Put pieces aa (Fig. 61) in position, with their tops quite flush with the tops of BB (Fig. 62), and solder them to the cylinder barrel and sides of the steam-way piece.

(3.) Solder the valve plate centrally to BB, and to the tops of aa, which must lie between the central and outside ports. Take great care to make steam-tight joints here, and to have the plate parallel to the standards in one direction and to the cylinder in the other.

(4.) Solder in pieces bb. These should be a tight fit, as it is difficult to hold them in place while soldering is done.

(5.) Bore a 5/16-inch hole in the lower side of the central division and solder on the exhaust pipe.

Slide Valve.—The contact part of this is cut out of flat sheet brass (Fig. 63), and to one side is soldered a cap made by turning down the edges of a cross with very short arms. The little lugs aa are soldered to this, and slotted with a jeweller’s file to engage with notches cut in the valve rod (see Figs. 58 and 62).

[Illustration: FIG. 63.-Parts of slide valve.]

The Crank and Crank Shaft.—The next thing to take in hand is the fixing of the crank shaft. This is a piece of 3/8 or 1/2 inch steel rod 5 inches long.

The bearings for this may be pieces of brass tubing, fitting the rod fairly tight. By making them of good length—1 inch—the wear is reduced to almost nothing if the lubricating can is used as often as it should be.

Each bearing is shown with two standards. The doubling increases rigidity, and enables an oil cup to be fixed centrally.

The shape of the standards will be gathered from Fig. 53, their outline being dotted in behind the crank.

Cut out and bend the standards—after drilling the holes for the foot screws—before measuring off for the centres of the holes; in fact, follow the course laid down with regard to the cylinder standards.

Make a bold scratch across the bedplate to show where the centre line of the shaft should be, and another along the bed for the piston-rod centre line. (Position given on p. 138.)

Bore holes in the bearings for the oil cups, which may be merely forced in after the engine is complete.

The crank boss may be made out of a brass disc 2-3/4 inches diameter and 3/16 inch thick, from which two curved pieces are cut to reduce the crank to the shape shown in Fig. 53. The heavier portion, on the side of the shaft away from the crank pin, helps to counterbalance the weight of the connecting and piston rods. In Fig. 54 (plan of engine) you will see that extra weight in this part has been obtained by fixing a piece of suitably curved metal to the back of the boss.

The mounting of the crank boss on the shaft and the insertion of the crank pin into the boss might well be entrusted to an expert mechanic, as absolute “squareness” is essential for satisfactory working. Screw-thread attachments should be used, and the crankshaft should project sufficiently to allow room for a flat lock nut. The crank pin will be rendered immovable by a small lock screw penetrating the boss edgeways and engaging with a nick in the pin.

Fixing the Standards and Bearings.—Place the two bearings in their standards and slip the crank shaft through them. Place standards on the bed, with their centre lines on the crank-shaft centre line. The face of the crank should be about 3/8 inch away from the piston rod centre line. Bring the nearer bearing up against the back of the disc, and arrange the standards equidistantly from the ends of the bearing. The other bearing should overlap the edge of the bed by about 1/8 inch. Get all standards square to the edge of the bed, and mark off the positions of screw holes in bed. Remove the standards, drill and tap the bed-plate holes, and replace parts as before, taking care that the lubricating holes in the bearings point vertically upwards. Then solder bearings to standards.

If any difficulty is experienced in getting all four standards to bed properly, make the bearing holes in the two inner ones a rather easy fit. The presence of the crank-shaft will assure the bearings being in line when the soldering is completed.

The standards and bed should have matching marks made on them.

The Eccentric.—This can be formed by soldering two thin brass discs 1-15/16-inch diameter concentrically to the sides of a disc of 1-15/16-inch diameter and 5/16 inch thick. The centre of the shaft hole must be exactly 9/32 inch from the centre of the eccentric to give the proper valve-travel. Drill and tap the eccentric edgeways for a lock screw.

A piece to which the eccentric strap, eccentric rod, and pump rod are attached is cut out of 5/16-inch brass. Its shape is indicated in Fig. 53. The side next the eccentric must be shaped as accurately as possible to the radius of the eccentric. The strap, of strip brass, is fastened to the piece by four screws, the eccentric rod by two screws.

Crosshead and Guides.—The crosshead (Figs. 53 and 54) is built up by soldering together a flat foot of steel, a brass upright, and a tubular top fitting the piston rod. The guides, which consist of a bed, covers, and distance-pieces united by screws (Fig. 64), have to withstand a lot of wear, and should preferably be of steel. The importance of having them quite flat and straight is, of course, obvious.

[Illustration: FIG. 64.—Cross section of crosshead and guide.]

The last 1-3/8 inches of the piston rod has a screw thread cut on it to engage with a threaded hole in the fork (cut out of thick brass plate), to which the rear end of the connecting rod is pinned, and to take the lock nut which presses the crosshead against this fork.

Assuming that all the parts mentioned have been prepared, the cylinder should be arranged in its proper place on the bed, the piston rod centrally over its centre line. Mark and drill the screw holes in the bed.

The Valve Gear.—We may now attend to the valve gear. A fork must be made for the end of the valve rod, and soldered to it with its slot at right angles to the slots which engage with the valve lugs. Slip the rod into the steam chest, put the valve on the rod, and attach the chest (without the cover) to the valve plate by a bolt at each corner. Pull the valve forward till the rear port is just uncovered, and turn the eccentric full forward. You will now be able to measure off exactly the distance between the centres of the valve-rod fork pin and the rear screw of the eccentric. The valve connecting rod (Fig. 53, VCR) should now be made and placed in position. If the two forward holes are filed somewhat slot-shaped, any necessary adjustment of the valve is made easier. If the adjustment of VCR and the throw of the eccentric are correct, the valve will just expose both end ports alternately when the crank is revolved. If one port is more exposed than the other, adjust by means of the eccentric screws till a balance is obtained. Should the ports still not be fully uncovered, the throw of the eccentric is too small, and you must either make a new eccentric or reduce the width of the valve. (The second course has the disadvantage of reducing the expansive working of the steam.) Excess movement, on the other hand, implies too great an eccentric throw.

Setting the Eccentric.—Turn the crank full forward, so that a line through the crank pin and shaft centres is parallel to the bed. Holding it in this position, revolve the eccentric (the screw of which should be slackened off sufficiently to allow the eccentric to move stiffly) round the shaft in a clockwise direction, until it is in that position below the shaft at which the front steam port just begins to show. Then tighten up the eccentric lock screw.[1]

[Footnote 1: The reader is referred to an excellent little treatise, entitled “The Slide Valve” (Messrs. Percival Marshall and Co., 26 Poppin’s Court, Fleet Street, E.C. Price 6d.), for a full explanation of the scientific principles of the slide valve.]

The Connecting Rod.—The length of this from centre to centre of the pins on which it works should be established as follows:—Slip over the piston rod a disc of card 1/32 inch thick. Then pass the rod through the gland and assemble the crosshead and fork on its end, and assemble the guides round the crosshead foot. Turn the crank pin full forward, pull the piston rod out as far as it will come, measure the distance between pin centres very carefully, and transfer it to a piece of paper.

The rod consists of a straight central bar and two rectangular halved ends. The ends should be cut out of brass and carefully squared. Through their exact centres drill 1/8-inch holes, and cut the pieces squarely in two across these holes. The sawed faces should be filed down to a good fit and soldered together. Now drill holes of the size of the pins, using what remains of the holes first made to guide the drill. The bolt holes are drilled next, and finally the holes for lubrication and those to take the rods. Then lay the two ends down on the piece of paper, so that their pinholes are centred on the centre marks, and the holes for the rod are turned towards one another. Cut off a piece of steel rod of the proper length and unsolder the ends. The rod pieces must then be assembled on the rod, and with it be centred on the paper and held in position while the parts are soldered together.

OTHER DETAILS.

Adjusting the Guides.—Put the connecting rod in place on its pins, and revolve the crank until the guides have taken up that position which allows the crosshead to move freely. Then mark off the holes for the guide holding-down screws, and drill and tap them.

Packings.—The glands and piston should be packed with asbestos string. Don’t be afraid of packing too tightly, as the tendency is for packing to get slacker in use. The rear end of the cylinder should be bevelled off slightly inside, to allow the packed piston to enter easily.

Joints.—The cylinder head and valve chest joints should be made with stout brown paper soaked in oil or smeared with red lead. All screw holes should be cut cleanly through the paper, and give plenty of room for the screws.

[Illustration: FIG. 66.-Vertical section of force pump driven by engine.]

When making a joint, tighten up the screws in rotation, a little at a time so as not to put undue strain on any screw. Wait an hour or two, and go round with the screw-driver again.

Lubrication.—When the engine is first put under steam, lubrication should be very liberal, to assure the parts “settling down” without undue wear.

The Pump.—Fig. 65 shows in section the pump, which will be found a useful addition to the engine. (For other details, see Figs. 53 and 54.) Its stroke is only that of the eccentric, and as the water passages and valves are of good size, it will work efficiently at high speed. The method of making it will be obvious from the diagrams, and space will therefore not be devoted to a detailed description. The valve balls should, of course, be of gun-metal or brass, and the seatings must be prepared for them by hammering in a steel ball of the same size.

In practice it is advisable to keep the pump always working, and to regulate the delivery to the boiler by means of a by-pass tap on the feed pipe, through which all or some of the water may be returned direct to the tank.

The tank, which should be of zinc, may conveniently be placed under the engine. If the exhaust steam pipe be made to traverse the tank along or near the bottom, a good deal of what would otherwise be wasted heat will be saved by warming the feed water.

Making a Governor.

[Illustration: FIG. 66.—Elevation of governor for horizontal engine. Above is plan of valve and rod gear.]

It is a great advantage to have the engine automatically governed, so that it may run at a fairly constant speed under varying loads and boiler pressures. In the absence of a governor one has to be constantly working the throttle; with one fitted, the throttle can be opened up full at the start, and the automatic control relied upon to prevent the engine knocking itself to pieces.

The vertical centrifugal apparatus shown in Fig. 66 was made by the writer, and acted very well. The only objection to it is its displacement of the pump from the bed. But a little ingenuity will enable the pump to be driven off the fly wheel end of the crank shaft, or, if the shaft is cut off pretty flush with the pulley, off a pin in the face of the pulley.

Turning to Fig. 66, A is a steel spindle fixed in a base, L, screwed to the bed. B is a brass tube fitting A closely, and resting at the bottom on a 1/4-inch piece of similar tubing pinned to A.

A wooden pulley jammed on B transmits the drive from a belt which passes at its other end round a similar, but slightly larger, pulley on the crank shaft. This pulley is accommodated by moving the eccentric slightly nearer the crank and shortening the fly-wheel side bearing a little.

The piece G, fixed to B by a lock screw, has two slots cut in it to take the upper ends of the weight links DD; and C, which slides up and down B, is similarly slotted for the links EE. Each of the last is made of two similarly shaped plates of thin brass, soldered together for half their length, but separated 3/32 inch at the top to embrace the projections of D. To prevent C revolving relatively to B, a notch is filed in one side of the central hole, to engage with a piece of brass wire soldered on B (shown solid black in the diagram). A spiral steel spring, indicated in section by a number of black dots, presses at the top against the adjustable collar F, and at the bottom against C.

The two weights WW are pieces of brass bar slotted for driving on to DD, which taper gently towards the outer edge.

When the pulley revolves, centrifugal force makes WW fly outwards against the pressure of the spring, and the links EE raise C, which in turn lifts the end of lever M. A single link, N, transmits the motion from a pin on M to the double bell-crank lever O (see Fig. 66) pivoted on a standard, P, attached to the bedplate. The slotted upper ends of P engage with pins on an adjustable block, R, which moves the governing valve V (solid black), working in the tube S through a gland. The higher M is raised the farther back is V moved, and its annular port is gradually pushed more out of line with two ports in the side of the valve tube, thus reducing the flow of steam from the supply pipe to the cylinder connection on the other side of the tube. This connection, by-the-bye, acts as fulcrum for lever M, which is made in two parts, held together by screws, to render detachment easy.

The closer the fit that V makes with S the more effective will the governing be. The gland at the end of S was taken from an old cylinder cover.

Regulation of the speed may be effected either

(1) by driving the governor faster or slower relatively to the speed of the crank shaft;

(2) by altering the position of W on D;

(3) by altering the compression of the spring by shifting F;

(4) by a combination of two or more of the above.

Generally speaking, (3) is to be preferred, as the simplest.

The belt may be made out of a bootlace or fairly stout circular elastic. In either case the ends should be chamfered off to form a smooth joint, which may be wrapped externally with thread.

FINAL HINTS.

All parts which have to be fitted together should have matching marks made on them with the punch. To take the parts of the valve chest as an example. As we have seen, these should be soldered together, finished off outside, and drilled. Before separating them make, say, two punch marks on what will be the upper edge of the valve plate near the end, and two similar marks on the chest as near the first as they can conveniently be. In like manner mark the chest cover and an adjacent part of the chest with three marks. It is utterly impossible to reassemble the parts incorrectly after separation if the marks are matched. Marking is of greatest importance where one piece is held up to another by a number of screws. If it is omitted in such a case, you may have a lot of trouble in matching the holes afterwards.

Jacket the cylinder with wood or asbestos, covered in neatly with sheet brass, to minimize condensation. If the steam ways, valve chest, and steam pipe also are jacketed, an increase in efficiency will be gained, though perhaps somewhat at the expense of appearance.

Boiler.—The boiler described on pp. 211-216, or a vertical multitubular boiler with about 800 sq. inches of heating surface will drive this engine satisfactorily.

XVI. MODEL STEAM TURBINES.

Steam turbines have come very much to the fore during recent years, especially for marine propulsion. In principle they are far simpler than cylinder engines, steam being merely directed at a suitable angle on to specially shaped vanes attached to a revolving drum and shaft. In the Parsons type of turbine the steam expands as it passes through successive rings of blades, the diameter of which rings, as well as the length and number of the blades, increases towards the exhaust end of the casing, so that the increasing velocity of the expanding steam may be taken full advantage of. The De Laval turbine includes but a single ring of vanes, against which the steam issues through nozzles so shaped as to allow the steam to expand somewhat and its molecules to be moving at enormous velocity before reaching the vanes. A De Laval wheel revolves at terrific speeds, the limit being tens of thousands of turns per minute for the smallest engines. The greatest efficiency is obtained, theoretically, when the vane velocity is half that of the steam, the latter, after passing round the curved inside surfaces of the vanes, being robbed of all its energy and speed. (For a fuller description of the steam turbine, see How It Works, Chap. III., pp.74-86.)

The turbines to be described work on the De Laval principle, which has been selected as the easier for the beginner to follow.

A Very Simple Turbine.

We will begin with a very simple contrivance, shown in Fig. 67. As a “power plant” it is confessedly useless, but the making of it affords amusement and instruction. For the boiler select a circular tin with a jointless stamped lid, not less than 4 inches in diameter, so as to give plenty of heating surface, and at least 2-1/2 inches deep, to ensure a good steam space and moderately dry steam. A shallow boiler may “prime” badly, if reasonably full, and fling out a lot of water with the steam.

Clean the metal round the joints, and punch a small hole in the lid, half an inch from the edge, to give egress to the heated air during the operation of soldering up the point or joints, which must be rendered absolutely water-tight.

[Illustration: FIG. 67.—Simple steam turbine.]

For the turbine wheel take a piece of thin sheet iron or brass; flatten it out, and make a slight dent in it an inch from the two nearest edges. With this dent as centre are scribed two circles, of 3/4 and 1/2 inch radius respectively. Then scratch a series of radial marks between the circles, a fifth of an inch apart. Cut out along the outer circle, and with your shears follow the radial lines to the inner circle. The edge is thus separated into vanes (Fig. 68), the ends of which must then be twisted round through half a right angle, with the aid of a pair of narrow-nosed pliers, care being taken to turn them all in the same direction.

[Illustration: FIG. 68.—Wheel for steam turbine, showing one vane twisted into final position.]

A spindle is made out of a large pin, beheaded, the rough end of which must be ground or filed to a sharp point. Next, just break through the metal of the disc at the centre with a sharpened wire nail, and push the spindle through till it projects a quarter of an inch or so. Soldering the disc to the spindle is most easily effected with a blowpipe or small blow-lamp.

The Boiler.—In the centre of the boiler make a dent, to act as bottom bearing for the spindle. From this centre describe a circle of 5/8-inch radius. On this circle must be made the steam port or ports. Two ports, at opposite ends of a diameter, give better results than a single port, as equalizing the pressure on the vanes, so that the spindle is relieved of bending strains. Their combined area must not, however, exceed that of the single port, if one only be used. It is important to keep in mind that for a turbine of this kind velocity of steam is everything, and that nothing is gained by increasing the number or size of ports if it causes a fall in the boiler pressure.

The holes are best made with a tiny Morse twist drill. As the metal is thin, drill squarely, so that the steam shall emerge vertically.

For the upper bearing bend a piece of tin into the shape shown in Fig. 67. The vertical parts should be as nearly as possible of the same length as the spindle. In the centre of the underside of the standard make a deep dent, supporting the metal on hard wood or lead, so that it shall not be pierced. If this accident occurs the piece is useless.

Place the wheel in position, the longer part of the spindle upwards, and move the standard about until the spindle is vertical in all directions. Scratch round the feet of the standard to mark their exact position, and solder the standard to the boiler. The top of the standard must now be bent slightly upwards or downwards until the spindle is held securely without being pinched.

A 3/16-inch brass nut and screw, the first soldered to the boiler round a hole of the same size as its internal diameter, make a convenient “filler;” but a plain hole plugged with a tapered piece of wood, such as the end of a penholder, will serve.

Half fill the boiler by immersion in hot water, the large hole being kept lowermost, and one of the steam vents above water to allow the air to escape.

A spirit lamp supplies the necessary heat. Or the boiler may be held in a wire cradle over the fire, near enough to make the wheel hum. Be careful not to over-drive the boiler. As a wooden plug will probably be driven out before the pressure can become dangerous, this is a point in favour of using one. Corrosion of the boiler will be lessened if the boiler is kept quite full of water when not in use.

A Practical Steam Turbine.

The next step takes us to the construction of a small turbine capable of doing some useful work. It is shown in cross section and elevation in Fig. 69.

[Illustration: FIG. 69.—Model steam turbine, showing vertical cross section (left) and external steam pipe (right).]

The rotor in this instance is enclosed in a case made up of two stout brass discs, D and E, and a 3/4-inch length of brass tubing. The plates should be 1/2-inch larger in diameter than the ring, if the bolts are to go outside. The stouter the parts, within reason, the better. Thick discs are not so liable to cockle as thin ones, and a stout ring will make it possible to get steam-tight joints with brown-paper packing.

The wheel is a disc of brass, say, 1/25 inch thick and 4 inches in diameter; the spindle is 3/16 inch, of silver steel rod; the bearings, brass tubing, making a close fit on the rod.

If you cannot get the ring ends turned up true in a lathe—a matter of but a few minutes’ work—rub them down on a piece of emery cloth supported on a true surface, such as a piece of thick glass.

Now mark out accurately the centres of the discs on both sides, and make marks to show which face of each disc is to be outside.

On the outside of both scribe circles of the size of the bearing tubes, and other circles at the proper radius for the bolt hole centres.

On the outside of D scribe two circles of 2-inch and 1-11/16-inch radius, between which the steam pipe will lie.

On the inside of D scribe a circle of 1-27/32-inch radius for the steam ports.

On the outside of E mark a 7/8-inch circle for the exhaust pipe.

On the inside of both mark the circles between which the ring must lie.

Bolt Holes.—The marks for these, six or twelve in number, are equally spaced on the outside of one plate, and the two plates are clamped or soldered together before the boring is done, to ensure the holes being in line. If the bolts are to screw into one plate, be careful to make the holes of the tapping size in the first instance, and to enlarge those in D afterwards. Make guide marks in the plates before separating, between what will be the uppermost holes and the circumference.

Bolts.—These should be of brass if passed inside the ring. Nuts are not necessary if E is tapped, but their addition will give a smarter appearance and prevent-the bolts becoming loose.

Bearings.—Bore central holes in the discs to a good fit for the bearings, and prepare the hole for the exhaust pipe. This hole is most easily made by drilling a ring of small holes just inside the mark and cutting through the intervening metal.

For A, B, and C cut off pieces of bearing pipe, 1/2, 1/4, and 3/4 inch long respectively, and bevel the ends of B and C as shown, to minimize friction if they rub. File all other ends square. (Lathe useful here.)

Bore oil holes in B and C, and clear away all the “burr.” Make scratches on the bearings to show how far they should be pushed through the case.

Now assemble the case, taking care that the edge of the ring corresponds exactly with the circles marked on the discs, and clean the metal round the bearing holes and the bearings themselves. The last are then placed in position, with the lubricating holes pointing upwards towards the guide marks on the discs. Push the spindle rod through the bearings, which must be adjusted until the rod can be revolved easily with the fingers. Then solder in the bearing with a “Tinol” lamp.

The Wheel.—Anneal this well by heating to a dull red and plunging it in cold water. Mark a circle of 1-1/4-inch radius, and draw radial lines 1/4 inch apart at the circumference from this circle to the edge. Cut out along the lines, and twist the vanes to make an angle of about 60 degree with the central part, and bend the ends slightly backward away from the direction in which the rotor will revolve. (The directions given on p. 189 for making a steam top wheel can be applied here.)

Bore a hole in the centre to make a tight fit with the spindle, and place the rotor in position, with piece B in contact on the C side. Get everything square (rotation will betray a bad wobble), and solder the three parts together with the blow-lamp.

Mount the rotor squarely by the spindle points between two pieces of wood held lightly in the vice, and, with the aid of a gauge fixed to the piece nearest the wheel, true up the line of the vanes. (Lathe useful here.)

The Steam Pipe is 15 inches (or more) of 5/16-inch copper tubing, well annealed. To assist the bending of it into a ring one needs some circular object of the same diameter as the interior diameter of the ring round which to curve it. I procured a tooth-powder box of the right size, and nailed it firmly to a piece of board. Then I bevelled off the end of the pipe to the approximately correct angle, laid it against the box, and drove in a nail to keep it tight up. Bending was then an easy matter, a nail driven in here and there holding the pipe until the ring was complete. I then soldered the end to the standing part, and detached the ring for flattening on one side with a file and emery cloth. This done, I bored a hole through the tube at F to open up the blind end of the ring.

Attaching the ring to disc D is effected as follows:—Tin the contact faces of the ring and disc pretty heavily with solder, after making poppet marks round the guide circles so that they may not be lost under the solder. The ring must be pressed tightly against its seat while heating is done with the lamp. An extra pair of hands makes things easier at this point. Be careful not to unsolder the spindle bearing, a thing which cannot happen if the bearing is kept cool by an occasional drop or two of water. A little extra solder should be applied round the points where the ports will be.

The Steam Ports.—These are drilled (with a 1/32-inch twist drill), at an angle of about 30 degrees to the plate, along the circle already scribed. If you have any doubt as to your boiler’s capacity, begin with one hole only, and add a second if you think it advisable. As already remarked, pressure must not be sacrificed to steam flow.

Lubricators.—These are short pieces of tubing hollowed at one end by a round file of the same diameter as the bearings. A little “Tinol” is smeared over the surfaces to be joined, and the lubricators are placed in position and heated with the blow-lamp until the solder runs. To prevent the oil flowing too freely, the lubricators should be provided with airtight wooden plugs.

Escape Pipes.—The pipe for the exhaust steam is now soldered into disc E, and a small water escape into the ring at its lowest point. This pipe should be connected with a closed chamber or with the exhaust at a point lower than the base of the turbine case.

Stirrup.—Fig. 69 shows a stirrup carrying a screw which presses against the pulley end of the spindle. This attachment makes it easy to adjust the distance between the rotor and the steam ports, and also concentrates all end thrust on to a point, thereby minimizing friction. The stirrup can be fashioned in a few minutes out of brass strip. Drill the holes for the holding-on screws; drill and tap a hole for the adjusting screw; insert the screw and centre it correctly on the spindle point. Then mark the position of the two screw holes in E; drill and tap them.

Feet are made of sheet brass, drilled to take the three (or two) lowermost bolts, and bent to shape. Note.—A side and foot may be cut out of one piece of metal. The difficulty is that the bending may distort the side, and prevent a tight joint between side and ring.

Assembling.—Cut out two rings of stout brown paper a quarter of an inch wide and slightly larger in diameter than the casing ring. In assembling the turbine finally, these, after being soaked in oil, should be inserted between the ring and the discs. Put in four screws only at first, and get the ring properly centred and the bearings exactly in line, which will be shown by the spindle revolving easily. Then tighten up the nuts and insert the other bolts, the three lowest of which are passed through the feet. Affix the pulley and stirrup, and adjust the spindle longitudinally until the rotor just does not rub the casing. The soldering on of the cap of A completes operations.

To get efficiency, heavy gearing down is needed, and this can be managed easily enough with the help of a clockwork train, decreasing the speed five or more times for driving a dynamo, and much more still for slow work, such as pumping.

A More Elaborate Turbine.

[Illustration: FIG. 70.—Vertical section of steam turbine with formed blades (left); outside view of turbine, gear side (right).]

The turbine just described can hardly be termed an efficient one, as the vanes, owing to their simple formation, are not shaped to give good results. We therefore offer to our readers a design for a small turbine of a superior character. This turbine is shown in elevation and section in Fig. 70. The casing is, as in the preceding instance, made up of flat brass plates and a ring of tubing, and the bearings, BG1, BG2, of brass tube. But the wheel is built up of a disc 3 inches in diameter, round the circumference of which are 32 equally-spaced buckets, blades, or vanes, projecting 5/8 inch beyond the edge of the disc. The wheel as a whole is mounted on a spindle 3-1/8 inches long, to which it is secured by three nuts, N1 N2 N3. One end of the spindle is fined down to take a small pinion, P1, meshing with a large pinion, P2, the latter running in bearings, BG3, in the wheel-case and cover. The drive of the turbine is transmitted either direct from the axle of P2 or from a pulley mounted on it.

CONSTRUCTION.

[Illustration: FIG. 71.—Plate marked out for turbine wheel blades. B is blade as it appears before being curved.]

The Wheel.—If you do not possess a lathe, the preparation of the spindle and mounting the wheel disc on it should be entrusted to a mechanic. Its diameter at the bearings should be 5/32 inch or thereabouts. (Get the tubing for the bearings and for the spindle turned to fit.) The larger portion is about twice as thick as the smaller, to allow room for the screw threads. The right-hand end is turned down quite small for the pinion, which should be of driving fit.

The Blades.—Mark out a piece of sheet iron as shown in Fig. 71 to form 32 rectangles, 1 by l/2 inch. The metal is divided along the lines aaaa, bbbb, and ab, ab, ab, ab, etc. The piece for each blade then has a central slot 5/16 inch long and as wide as the wheel disc cut very carefully in it.

Bending the Blades.—In the edge of a piece of hard wood 1 inch thick file a notch 3/8 inch wide and 1/8 inch deep with a 1/2-inch circular file, and procure a metal bar which fits the groove loosely. Each blade is laid in turn over the groove, and the bar is applied lengthwise on it and driven down with a mallet, to give the blade the curvature of the groove. When all the blades have been made and shaped, draw 16 diameters through the centre of the wheel disc, and at the 32 ends make nicks 1/16 inch deep in the circumference.

True up the long edges of the blades with a file, and bring them off to a sharp edge, removing the metal from the convex side.

Fixing the Blades.—Select a piece of wood as thick as half the width of a finished blade, less half the thickness of the wheel disc. Cut out a circle of this wood 2 inches in diameter, and bore a hole at the centre. The wheel disc is then screwed to a perfectly flat board or plate, the wooden disc being used as a spacer between them.

Slip a blade into place on the disc, easing the central slit, if necessary, to allow the near edge to lie in contact with the board—that is parallel to the disc. Solder on the blade, using the minimum of solder needed to make a good joint. When all the blades are fixed, you will have a wheel with the blades quite true on one side. It is, therefore, important to consider, before commencing work, in which direction the concave side of the blades should be, so that when the wheel is mounted it shall face the nozzle.

To make this point clear: the direction of the nozzle having been decided, the buckets on the trued side must in turn present their concave sides to the nozzle. In Fig. 70 the nozzle points downwards, and the left side of the wheel has to be trued. Therefore B1 has its convex, B2 its concave, side facing the reader, as it were.

The Nozzle is a 1-1/2 inch piece of brass bar. Drill a 1/20-inch hole through the centre. On the outside end, enlarge this hole to 1/8 inch to a depth of 1/8 inch. The nozzle end is bevelled off to an angle of 20 degrees, and a broach is inserted to give the steam port a conical section, as shown in Fig. 72, so that the steam may expand and gain velocity as it approaches the blades. Care must be taken not to allow the broach to enter far enough to enlarge the throat of the nozzle to more than 1/20 inch.

[Illustration: FIG. 72.—Nozzle of turbine, showing its position relatively to buckets.]

Fixing the Nozzle.—The centre of the nozzle discharge opening is 1-13/16-inches from the centre of the wheel. The nozzle must make an angle of 20 degrees with the side of the casing, through which it projects far enough to all but touch the nearer edges of the vanes. (Fig. 72.) The wheel can then be adjusted, by means of the spindle nuts, to the nozzle more conveniently than the nozzle to the wheel. To get the hole in the casing correctly situated and sloped, begin by boring a hole straight through, 1/4 inch away laterally from where the steam discharge hole will be, centre to centre, and then work the walls of the hole to the proper angle with a circular file of the same diameter as the nozzle piece, which is then sweated in with solder. It is, of course, an easy matter to fix the nozzle at the proper angle to a thin plate, which can be screwed on to the outside of the casing, and this method has the advantage of giving easy detachment for alteration or replacement.

Balancing the Wheel.—As the wheel will revolve at very high speed, it should be balanced as accurately as possible. A simple method of testing is to rest the ends of the spindle on two carefully levelled straight edges. If the wheel persists in rolling till it takes up a certain position, lighten the lower part of the wheel by scraping off solder, or by cutting away bits of the vanes below the circumference of the disc, or by drilling holes in the disc itself.

Securing the Wheel.—When the wheel has been finally adjusted relatively to the nozzle, tighten up all the spindle nuts hard, and drill a hole for a pin through them and the disc parallel to the spindle, and another through N3 and the spindle. (Fig. 70.)

Gearing.—The gear wheels should be of good width, not less than 3/16 inch, and the smaller of steel, to withstand prolonged wear. Constant lubrication is needed, and to this end the cover should make an oil-tight fit with the casing, so that the bottom of the big pinion may run in oil. To prevent overfilling, make a plug-hole at the limit level, and fit a draw-off cock in the bottom of the cover. If oil ducts are bored in the bearing inside the cover, the splashed oil will lubricate the big pinion spindle automatically.

[Illustration: FIG. 73.—Perspective view of completed turbine.]

General—The sides of the casing are held against the drum by six screw bolts on the outside of the drum. The bottom of the sides is flattened as shown (Fig. 70), and the supports, S1 S2, made of such a length that when they are screwed down the flattened part is pressed hard against the bed. The oil box on top of the casing has a pad of cotton wool at the bottom to regulate the flow of oil to the bearings. Fit a drain pipe to the bottom of the wheel-case.

Testing.—If your boiler will make steam above its working pressure faster than the turbine can use it, the nozzle may be enlarged with a broach until it passes all the steam that can be raised; or a second nozzle may be fitted on the other end of the diameter on which the first lies. This second nozzle should have a separate valve, so that it can be shut off.

XVII. STEAM TOPS.

A very interesting and novel application of the steam turbine principle is to substitute for a wheel running in fixed bearings a “free” wheel pivoted on a vertical spindle, the point of which takes the weight, so that the turbine becomes a top which can be kept spinning as long as the steam supply lasts.

These toys, for such they must be considered, are very easy to make, and are “warranted to give satisfaction” if the following instructions are carried out.

A Small Top.—Fig. 74 shows a small specimen, which is of the self-contained order, the boiler serving as support for the top.

[Illustration: FIG. 74.-Simplest form of steam top.] [1]

[Footnote 1: Spirit lamp shown for heating boiler.]

For the boiler use a piece of brass tubing 4 inches or so in diameter and 3 inches long. (The case of an old brass “drum” clock, which may be bought for a few pence at a watchmaker’s, serves very well if the small screw holes are soldered over.) The ends should be of brass or zinc, the one which will be uppermost being at least 1/16 inch thick. If you do not possess a lathe, lay the tube on the sheet metal, and with a very sharp steel point scratch round the angle between tube and plate on the inside. Cut out with cold chisel or shears to within 1/16 inch of the mark, and finish off carefully—testing by the tube now and then—to the mark. Make a dent with a centre punch in the centre of the top plate for the top to spin in.

[Illustration: FIG. 75.—Wheel of steam top, ready for blades to be bent. A hole is drilled at the inner end of every slit to make bending easier.]

Solder the plates into the tube, allowing an overlap of a quarter of an inch beyond the lower one, to help retain the heat.

The top wheel is cut out of a flat piece of sheet iron, zinc, or brass. Its diameter should be about 2-1/2 inches, the vanes 1/2 inch long and 1/4 inch wide at the circumference. Turn them over to make an angle of about 45 degrees with the spindle. They will be more easily bent and give better results if holes are drilled, as shown in Fig. 75.

The spindle is made out of a bit of steel or wire—a knitting-needle or wire-nail—not more than 1 inch in diameter and 1-1/2 inches long. The hole for this must be drilled quite centrally in the wheel; otherwise the top will be badly balanced, and vibrate at high speeds. For the same reason, the spindle requires to be accurately pointed.

The steam ports are next drilled in the top of the boiler. Three of them should be equally spaced (120 degrees apart) on a circle of 1-inch radius drawn about the spindle poppet as centre. The holes must be as small as possible—1/40 to 1/50 inch—and inclined at an angle of not more than 45 degrees to the top plate. The best drills for the purpose are tiny Morse twists, sold at from 2d. to 3d. each, held in a pin vice rotated by the fingers. The points for drilling should be marked with a punch, to give the drills a hold. Commence drilling almost vertically, and as the drill enters tilt it gradually over till the correct angle is attained.

If a little extra trouble is not objected to, a better job will be made of this operation if three little bits of brass, filed to a triangular section (Fig. 76 a), are soldered to the top plate at the proper places, so that the drilling can be done squarely to one face and a perfectly clear hole obtained. The one drawback to these additions is that the vanes of the turbine may strike them. As an alternative, patches may be soldered to the under side of the plate (Fig. 76, b) before it is joined to the barrel; this will give longer holes and a truer direction to the steam ports.

[Illustration: FIG. 76. Steam port details.]

Note that it is important that the ports should be all of the same diameter and tangential to the circle on which they are placed, and all equally inclined to the plate. Differences in size or direction affect the running of the top.

Solder the spindle to the wheel in such a position that the vanes clear the boiler by an eighth of an inch or so. If tests show that the top runs quite vertically, the distance might be reduced to half, as the smaller it is the more effect will the steam jets have.

A small brass filler should be affixed to the boiler halfway up. A filler with ground joints costs about 6d.

A wick spirit lamp will serve to raise steam. Solder to the boiler three legs of such a length as to give an inch clearance between the lamp wick and the boiler. If the wick is arranged to turn up and down, the speed of the top can be regulated.

A Large Top.—The top just described must be light, as the steam driving it is low-pressure, having free egress from the boiler, and small, as the steam has comparatively low velocity. The possessor of a high-pressure boiler may be inclined to make something rather more ambitious—larger, heavier, and useful for displaying spectrum discs, etc.

The top shown in Fig. 77 is 3 inches in diameter, weighs 1 oz., and was cut out of sheet-zinc. It stands on a brass disc, round the circumference of which is soldered a ring of 5/32-inch copper tubing, furnished with a union for connection with a boiler.

[Illustration: FIG. 77.—-Large steam top and base.]

The copper tubing must be well annealed, so as to bend quite easily. Bevel off one end, and solder this to the plate. Bend a couple of inches to the curve of the plate, clamp it in position, and solder; and so on until the circle is completed, bringing the tube snugly against the bevelled end. A hole should now be drilled through the tube into this end—so that steam may enter the ring in both directions-and plugged externally.

By preference, the ring should be below the plate, as this gives a greater thickness of metal for drilling, and also makes it easy to jacket the tube by sinking the plate into a wooden disc of somewhat greater diameter.

Under 50 lbs. of steam, a top of this kind attains a tremendous velocity. Also, it flings the condensed steam about so indiscriminately that a ring of zinc 3 inches high and 18 inches in diameter should be made wherewith to surround it while it is running.

If a little bowl with edges turned over be accurately centred on the wheel, a demonstration of the effects of centrifugal force may be made with water, quicksilver, or shot, which fly up into the rim and disappear as the top attains high speed, and come into sight again when its velocity decreases to a certain figure. A perforated metal globe threaded on the spindle gives the familiar humming sound.

A spectrum disc of the seven primary colours—violet, indigo, blue, green, yellow, orange, red—revolved by the top, will appear more or less white, the purity of which depends on the accuracy of the tints used.

XVIII. MODEL BOILERS.

A chapter devoted to the construction of model boilers may well open with a few cautionary words, as the dangers connected with steam-raisers are very real; and though model-boiler explosions are fortunately rare, if they do occur they may be extremely disastrous.

Therefore the following warnings:—

(1.) Do not use tins or thin sheet iron for boilers. One cannot tell how far internal corrosion has gone. The scaling of 1/100 inch of metal off a “tin” is obviously vastly more serious than the same diminution in the thickness of, say, a 1/4-inch plate. Brass and copper are the metals to employ, as they do not deteriorate at all provided a proper water supply be maintained.

(2.) If in doubt, make the boiler much more solid than is needed, rather than run any risks.

(3.) Fit a steam gauge, so that you may know what is happening.

(4.) Test your boiler under steam, and don’t work it at more than half the pressure to which it has been tested. (See p. 220.)

In the present chapter we will assume that the barrels of all the boilers described are made out of solid-drawn seamless copper tubing, which can be bought in all diameters up to 6 inches, and of any one of several thicknesses. Brass tubing is more easily soldered, but not so good to braze, and generally not so strong as copper, other things being equal. Solid-drawn tubing is more expensive than welded tubing or an equivalent amount of sheet metal, but is considerably stronger than the best riveted tube.

Boiler ends may be purchased ready turned to size. Get stampings rather than castings, as the first are more homogeneous, and therefore can be somewhat lighter.

Flanging Boiler Ends.—To make a good job, a plate for an end should be screwed to a circular block of hard wood (oak or boxwood), having an outside diameter less than the inside diameter of the boiler barrel by twice the thickness of the metal of the end, and a rounded-off edge. The plate must be annealed by being heated to a dull red and dipped in cold water. The process must be repeated should the hammering make the copper stubborn.

Stays should be used liberally, and be screwed and nutted at the ends. As the cutting of the screw thread reduces the effective diameter, the strength of a stay is only that of the section at the bottom of the threads.

Riveting.—Though stays will prevent the ends of the boiler blowing off, it is very advisable to rivet them through the flanges to the ends of the barrel, as this gives mutual support independently of soldering or brazing. Proper boiler rivets should be procured, and annealed before use. Make the rivet holes a good fit, and drill the two parts to be held together in one operation, to ensure the holes being in line. Rivets will not close properly if too long. Dies for closing the rivet heads may be bought for a few pence.

Soldering, etc.—Joints not exposed directly to the furnace flames may be soldered with a solder melting not below 350 degrees Fahr. Surfaces to be riveted together should be “tinned” before riveting, to ensure the solder getting a good hold afterwards. The solder should be sweated right through the joint with a blow-lamp to make a satisfactory job.

All joints exposed to the flames should be silver-soldered, and other joints as well if the working pressure is to exceed 50 lbs. to the square inch. Silver-soldering requires the use of a powerful blow—lamp or gas-jet; ordinary soft soldering bits and temperatures are ineffective. Brazing is better still, but should be done by an expert, who may be relied on not to burn the metal. It is somewhat risky to braze brass, which melts at a temperature not far above that required to fuse the spelter (brass solder). Getting the prepared parts of a boiler silver-soldered or brazed together is inexpensive, and is worth the money asked.

[Illustration: FIG. 78.]

Some Points in Design.

The efficiency of a boiler is governed chiefly (1) by the amount of heating surface exposed to the flames; (2) by the distribution of the heating surface; (3) by the amount of fuel which can be burnt in the furnace in a given time; (4) by avoiding wastage of heat.

The simplest form of boiler, depicted in Fig. 78, is extremely inefficient because of its small heating surface. A great deal of the heat escapes round the sides and the ends of the boiler. Moreover, a good deal of the heat which passes into the water is radiated out again, as the boiler is exposed directly to the air.

Fig. 79 shows a great improvement in design. The boiler is entirely enclosed, except at one end, so that the hot gases get right round the barrel, and the effective heating surface has been more than doubled by fitting a number of water-tubes, aaa, bbbb, which lie right in the flames, and absorb much heat which would otherwise escape. The tubes slope upwards from the chimney end, where the heat is less, to the fire-door end, where the heat is fiercer, and a good circulation is thus assured. The Babcock and Wilcox boiler is the highest development of this system, which has proved very successful, and may be recommended for model boilers of all sizes. The heating surface may be increased indefinitely by multiplying the number of tubes. If a solid fuel-coal, coke, charcoal, etc.-fire is used, the walls of the casing should be lined with asbestos or fire-clay to prevent the metal being burnt away.

[Illustration: FIG. 79—Side and end elevations of a small water-tube boiler.]

The horizontal boiler has an advantage over the vertical in that, for an equal diameter of barrel, it affords a larger water surface, and is, therefore, less subject to “priming,” which means the passing off of minute globules of water with the steam. This trouble, very likely to occur if the boiler has to run an engine too large for it, means a great loss of efficiency, but it may be partly cured by making the steam pass through coils exposed to the furnace gases on its way to the engine. This “superheating” evaporates the globules and dries the steam, besides raising its temperature. The small water-tube is preferable to the small fire-tube connecting furnace and chimney, as its surface is exposed more directly to the flames; also it increases, instead of decreasing, the total volume of water in the boiler.

A Vertical Boiler.

[Illustration: FIG. 80.—Details of vertical boiler.]

The vertical boiler illustrated by Fig. 80 is easily made. The absence of a water jacket to the furnace is partly compensated by fitting six water-tubes in the bottom. As shown, the barrel is 8 inches long and 6 inches in outside diameter, and the central flue 1-1/2 inches across outside solid-drawn 1/16-inch tubing, flanged ends, and four 1/4-inch stays—disposed as indicated in Fig. 80 (a) and (b)—are used. The 5/16 or 3/8 inch water-tubes must be annealed and filled with lead or resin before being bent round wooden templates. After bending, run the resin or lead out by heating. The outflow end of each pipe should project half an inch or so further through the boiler bottom than the inflow end.

Mark out and drill the tube holes in the bottom, and then the flue hole, for which a series of small holes must be made close together inside the circumference and united with a fret saw. Work the hole out carefully till the flue, which should be slightly tapered at the end, can be driven through an eighth of an inch or so. The flue hole in the top should be made a good fit, full size.

Rivet a collar, x (Fig. 80, a), of strip brass 1/4 inch above the bottom of the flue to form a shoulder. Another collar, y (Fig. 80, c), is needed for the flue above the top plate. Put the ends and flue temporarily in place, mark off the position of y, and drill half a dozen 5/32-inch screw holes through y and the flue. Also drill screw holes to hold the collar to the boiler top.

The steam-pipe is a circle of 5/16-inch copper tube, having one end closed, and a number of small holes bored in the upper side to collect the steam from many points at once. The other end is carried through the side of the boiler.

[Illustration: FIG. 81.—Perspective view of horizontal boiler mounted on wooden base.]

Assembling.—The order of assembling is:—Rivet in the bottom; put the steam-pipe in place; rivet in the top; insert the flue, and screw collar y to the top; expand the bottom of the flue by hammering so that it cannot be withdrawn; insert the stays and screw them up tight; silver-solder both ends of the flue, the bottom ends of the stays, and the joint between bottom and barrel. The water-tubes are then inserted and silver-soldered, and one finishes by soft-soldering the boiler top to the barrel and fixing in the seatings for the water and steam gauges, safety-valve, mud-hole, filler, and pump-if the last is fitted.

The furnace is lined with a strip of stout sheet iron, 7 inches wide and 19-1/4 inches long, bent round the barrel, which it overlaps for an inch and a half. Several screws hold lining and barrel together. To promote efficiency, the furnace and boiler is jacketed with asbestos—or fire-clay round the furnace—secured by a thin outer cover. The enclosing is a somewhat troublesome business, but results in much better steaming power, especially in cold weather. Air-holes must be cut round the bottom of the lining to give good ventilation.

A boiler of this size will keep a 1 by 1-1/2 inch cylinder well supplied with steam at from 30 to 40 lbs. per square inch.

A Horizontal Boiler.

[Illustration: FIG. 82.—Longitudinal section of large water-tube boiler.]

The boiler illustrated by Fig. 81 is designed for heating with a large paraffin or petrol blow-lamp. It has considerably greater water capacity, heating surface—the furnace being entirely enclosed—and water surface than the boiler just described. The last at high-water level is about 60, and at low-water level 70, square inches.

The vertical section (Fig. 82) shows 1/16-inch barrel, 13 inches long over all and 12 inches long between the end plates, and 6 inches in diameter. The furnace flue is 2-1/2 inches across outside, and contains eleven 1/2-inch cross tubes, set as indicated by the end view (Fig. 83), and 3/4 inch apart, centre to centre. This arrangement gives a total heating surface of about 140 square inches. If somewhat smaller tubes are used and doubled (see Fig. 84), or even trebled, the heating surface may be increased to 180-200 square inches. With a powerful blow-lamp this boiler raises a lot of steam.

Tubing the Furnace Flue.—Before any of the holes are made, the lines on which the centres lie must be scored from end to end of the flue on the outside. The positions of these lines are quickly found as follows:—Cut out a strip of paper exactly as long as the circumference of the tube, and plot the centre lines on it. The paper is then applied to the tube again, and poppet marks made with a centre punch opposite to or through the marks on the paper. Drive a wire-nail through a piece of square wood and sharpen the point. Lay the flue on a flat surface, apply the end of the nail to one of the poppet marks, and draw it along the flue, which must be held quite firmly. When all the lines have been scored, the centring of the water tubes is a very easy matter.

[Illustration: FIG. 83.-End of horizontal boiler, showing position of holes for stays and fittings.]

The two holes for any one tube should be bored independently, with a drill somewhat smaller than the tube, and be opened to a good fit with a reamer or broach passed through both holes to ensure their sides being in line. Taper the tubes—2-7/8 inches long each—slightly at one end, and make one of the holes a bit smaller than the other. The tapered end is passed first through the larger hole and driven home in the other, but not so violently as to distort the flue. If the tubes are made fast in this way, the subsequent silver-soldering will be all the easier.

[Illustration: FIG. 84.—Doubled cross tubes In horizontal boiler flue.]

The Steam Dome.—The large holes—2 inches in diameter—required for the steam dome render it necessary to strengthen the barrel at this point. Cut out a circular plate of metal 4 inches across, make a central hole of the size of the steam dome, and bend the plate to the curve of the inside of the barrel. Tin the contact faces of the barrel and “patch” and draw them together with screws or rivets spaced as shown in Fig. 85, and sweat solder into the joint. To make it impossible for the steam dome to blowout, let it extend half an inch through the barrel, and pass a piece of 1/4-inch brass rod through it in contact with the barrel. The joint is secured with hard solder. Solder the top of the dome in 1/8 inch below the end of the tube, and burr the end over. The joint should be run again afterwards to ensure its being tight.

[Illustration: FIG. 85.—Showing how to mark out strengthening patch round steam dome hole.]

The positions of stays and gauges is shown in Fig. 83.

Chimney.—This should be an elbow of iron piping fitting the inside of the flue closely, made up of a 9-inch and a 4-inch part. The last slips into the end of the flue; the first may contain a coil for superheating the steam.

A Multitubular Boiler.

[Illustration: FIG. 86.—Cross section of multitubular boiler.]

Figs. 86 and 87 are respectively end and side elevations of a multitubular boiler having over 600 square inches of heating surface—most of it contributed by the tubes—and intended for firing with solid fuel.

The boiler has a main water-drum, A, 5 inches in diameter and 18 inches long, and two smaller water-drums, B and C, 2-1/2 by 18 inches, connected by two series of tubes, G and H, each set comprising 20 tubes. The H tubes are not exposed to the fire so directly as the G tubes, but as they enter the main drum at a higher point, the circulation is improved by uniting A to B and C at both ends by large 1-inch drawn tubes, F. In addition, B and C are connected by three 3/4-inch cross tubes, E, which prevent the small drums spreading, and further equalize the water supply. A 1-1/2-inch drum, D, is placed on the top of A to collect the steam at a good distance from the water.

Materials.—In addition to 1-1/2 feet of 5 by 3/32 inch solid-drawn tubing for the main, and 3 feet of 2-1/2 by 1/16 inch tubing for the lower drums, the boiler proper requires 22-1/2 feet of 1/2-inch tubing, 19 inches of 3/4-inch tubing, 2-1/4 feet of 1-inch tubing, 1 foot of 1-1/2-inch tubing, and ends of suitable size for the four drums.

[Illustration: FIG. 87.—Longitudinal section of multitubular boiler.]

CONSTRUCTION.

[Illustration: FIG. 88.-Two arrangements for tube holes in multi tubular boiler.]

The centres for the water-tubes, G and H, should be laid out, in accordance with Fig. 88, on the tops of B and C and the lower part of A, along lines scribed in the manner explained on p. 207. Tubes H must be bent to a template to get them all of the same shape and length, and all the tubes be prepared before any are put in place. If the tubes are set 7/8 inch apart, centre to centre, instead of 1-1/4 inches, the heating surface will be greatly increased and the furnace casing better protected.

Assembling.—When all necessary holes have been made and are of the correct size, begin by riveting and silver-soldering in the ends of the drums. Next fix the cross tubes, E, taking care that they and B and C form rectangles. Then slip the F, G, and H tubes half an inch into the main drum, and support A, by means of strips passed between the G and H tubes, in its correct position relatively to B and C. The E tubes can now be pushed into B and C and silver-soldered. The supports may then be removed, and the a and H tubes be got into position and secured. Drum D then demands attention. The connecting tubes, KK, should be silver-soldered in, as the boiler, if properly made, can be worked at pressures up to 100 lbs. per square inch.

The casing is of 1/20-inch sheet iron, and in five parts. The back end must be holed to allow A, B, and C to project 1 inch, and have a furnace-door opening, and an airway at the bottom, 5 inches wide and 1 inch deep, cut in it. The airway may be provided with a flap, to assist in damping down the fire if too much steam is being raised. In the front end make an inspection opening to facilitate cleaning the tubes and removing cinders, etc.

The side plates, m m, are bent as shown in Fig. 86, and bolted to a semicircular top plate, n, bent to a radius of 6 inches. A slot, 1-1/2 inches wide and 11-1/2 inches long, must be cut in the top, n, to allow it to be passed over drum D; and there must also be a 3 or 3-1/2 inch hole for the chimney. A plate, p, covers in D. A little plate, o, is slipped over the slot in n, and asbestos is packed in all round D. The interior of the end, side, and the top plates should be lined with sheet asbestos held on by large tin washers and screw bolts. To protect the asbestos, movable iron sheets may be interposed on the furnace side. These are replaced easily if burnt away. The pieces m m are bent out at the bottom, and screwed down to a base-plate extending the whole length of the boiler.

The fire-bars fill the rectangle formed by the tubes B, El, and E2. A plate extends from the top of E2 to the front plate of the casing, to prevent the furnace draught being “short circuited.”

Boiler Fittings.

[Illustration: FIG. 89.-Safety valve.]

Safety Valves.—The best all-round type is that shown in Fig. 89. There is no danger of the setting being accidentally altered, as is very possible with a lever and sliding weight. The valve should be set by the steam gauge. Screw it down, and raise steam to the point at which you wish the safety valve to act, and then slacken off the regulating nuts until steam issues freely. The lock nuts under the cross-bar should then be tightened up. In the case of a boiler with a large heating surface, which makes steam quickly, it is important that the safety-valve should be large enough to master the steam. If the valve is too small, the pressure may rise to a dangerous height, even with the steam coming out as fast as the valve can pass it.

[Illustration: FIG. 90.-Steam gauge and siphon.]

Steam Gauges.—The steam gauge should register pressures considerably higher than that to be used, so that there may be no danger of the boiler being forced unwittingly beyond the limit registered. A siphon piece should be interposed between boiler and gauge (Fig. 90), to protect the latter from the direct action of the steam. Water condenses in the siphon, and does not become very hot.

[Illustration: FIG. 91.-Water gauge.]

Water Gauges should have three taps (Fig. 91), two between glass and boiler, to cut off the water if the glass should burst, and one for blowing off through. Very small gauges are a mistake, as the water jumps about in a small tube. When fitting a gauge, put packings between the bushes and the glass-holders, substitute a piece of metal rod for the glass tube, and pack the rod tightly. If the bushes are now sweated into the boiler end while thus directed, the gauge must be in line for the glass. This method is advisable in all cases, and is necessary if the boiler end is not perfectly flat.

Pumps.—Where a pump is used, the supply should enter the boiler below low-water level through a non-return valve fitted with a tap, so that water can be prevented from blowing back through the pump. As regards the construction of pumps, the reader is referred to p. 164 and to

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