Part II

., problem 134. A method very often adopted on working drawings is shown in fig. 15; here the thin lines represent the points, and the thick lines the roots of the threads. At fig. 16 is shown a more complete method. The simplest method is illustrated by figs. 10, 11, 13, and 14.

Here dotted lines are drawn parallel to the axis of the screw as far as it extends, and at a distance from one another equal to the diameter of the screw at the bottom of the thread.

[Illustration: FIG. 10.]

[Illustration: FIG. 11.]

_Forms of Nuts._--The most common form of nut is the hexagonal shown in figs. 10, 13, 14, 15, and 16; next to this comes the square nut shown in fig. 11. The method of drawing these nuts will be understood by reference to the figures; the small circles indicate the centres, and the inclined lines passing through them the radii of the curves which represent the chamfered or bevelled edge of the nut. In all the figures but the first the chamfer is just sufficient to touch the middle points of the sides, and in these cases the drawing of the nut is simpler.

[Illustration: FIG. 12.]

[Illustration: FIG. 13.]

[Illustration: FIG. 14.]

_Forms of Bolts._--At (_a_), fig. 12, is shown a bolt with a square head and a square neck. If this form of bolt is passed through a square hole the square neck prevents the bolt from turning when the nut is being screwed up. Instead of a square neck a snug may be used for the same purpose, as shown on the cup-headed bolt at (_b_). The snug fits into a short groove cut in the side of the hole through which the bolt passes. At (_a_) the diagonal lines are used to distinguish the flat side of the neck from the round part of the bolt above it. At (_c_) is shown a tee-headed bolt, and at (_d_) an eye-bolt. Fig. 13 represents a hook bolt. A bolt with a countersunk head is shown in fig. 11. If the countersunk head be lengthened so as to take up the whole of the unscrewed part of the bolt, we get the taper bolt shown in fig. 14, which is often used in the couplings of the screw shafts of steamships. The taper bolt has the advantage of having no projecting head, and it may also be made a tight fit in the hole with less trouble than a parallel bolt. Bolts may also have hexagonal heads.

[Illustration: FIG. 15]

[Illustration: FIG. 16]

_Studs_, or _stud bolts_, are shown in figs. 15 and 16; that in fig. 15 is a _plain stud_, while that in fig. 16 has an intermediate collar forged upon it, and is therefore called a _collared stud_.

_Proportions of Nuts and Bolt-heads._--In the hexagonal nut the diameter D across the flats is 1-1/2_d_ + 1/8, where _d_ is the diameter of the bolt. The same rule gives the width of a square nut across the flats. A rule very commonly used in making drawings of hexagonal nuts is to make the diameter D, across the angles equal to 2_d_. H, the height of the nut, is equal to the diameter of the bolt. In square and hexagonal headed bolts the height of the head varies from _d_ to 2/3_d_; the other dimensions are the same as for the corresponding nuts.

_Washers_ are flat, circular, wrought-iron plates, having holes in their centres of the same diameter as the bolts on which they are used. The object of the washer is to give a smooth bearing surface for the nut to turn upon, and it is used when the surfaces of the pieces to be connected are rough, or when the bolt passes through a hole larger than itself, as shown in fig. 10. The diameter of the washer is a little more than the diameter of the nut across the angles, and its thickness about 1/8 of the diameter of the bolt.

EXERCISE 12.--Draw, full size, the views shown in fig. 10 of an hexagonal nut and washer for a bolt 1-1/4 inches in diameter. The bolt passes through a hole 1-3/4 × 1-1/4. All the dimensions are to be calculated from the rules which have just been given.

EXERCISE 13.--Draw, full size, the plan and elevation of the square nut and bolt with countersunk head shown in fig. 11, to the dimensions given.

EXERCISE 14.--Draw, full size, the elevation of the hook bolt with hexagonal nut shown in fig. 13 to the dimensions given, and show also a plan.

EXERCISE 15.--Draw, to a scale of 4 inches to a foot, the conical bolt for a marine shaft coupling shown in fig. 14. All the parts are of wrought iron.

EXERCISE 16.--Fig. 15 is a section of the mouth of a small steam-engine cylinder, showing how the cover is attached; draw this full size.

EXERCISE 17.--Fig. 16 shows the central portion of the india-rubber disc valve which is described on page 68. A is the central boss of the grating, into which is screwed the stud B, upon which is forged the collar C. The upper part of the stud is screwed, and carries the guard D and an hexagonal nut E. F is the india-rubber. The grating and guard are of brass. The stud and nut are of wrought iron. Draw full size the view shown.

_Lock Nuts._--In order that a nut may turn freely upon a bolt, there is always a very small clearance space between the threads of the nut and those of the bolt. This clearance is shown exaggerated at (_a_), fig. 17, where A is a portion of a bolt within a nut B. Suppose that the bolt is stretched by a force W. When the nut B is screwed up, the upper surfaces of the projecting threads of the nut will press on the under surfaces of the threads of the bolt with a force P equal and opposite to W, as shown at (_b_), fig. 17. When in this condition the nut has no tendency to slacken back, because of the friction due to the pressure on the nut. Now suppose that the tension W on the bolt is momentarily diminished, then the friction which opposes the turning of the nut may be so much diminished that a vibration may cause it to slacken back through a small angle. If this is repeated a great many times the nut may slacken back so far as to become useless.

[Illustration: FIG. 17.]

[Illustration: FIG. 18.]

A very common arrangement for locking a nut is shown at (_a_), fig. 18. C is an ordinary nut, and B one having half the thickness of C. B is first screwed up tight so as to act on the bolt, as shown at (_b_), fig. 17. C is then screwed on top of B. When C is almost as tight as it can be made, it is held by one spanner, while B is turned back through a small angle with another. The action of the nuts upon the bolt and upon one another is now as shown at (_b_), fig. 18. It will be seen that the nuts are wedged tight on to the bolt, and that this action is independent of the tension W in the bolt. The nuts will, therefore, remain tight after the tension in the bolt is removed.

It is evident that if the nuts are screwed up in the manner explained, the outer nut C will carry the whole load on the bolt; hence C should be the thicker of the two nuts. In practice, the thin nut, called the lock nut, is often placed on the outside, for the reason that ordinary spanners are too thick to act on the thin nut when placed under the other.

Another very common arrangement for locking a nut is shown in fig. 19. A is the bolt and B the nut, the lower part of which is turned circular. A groove C is also turned on the nut at this part. The circular part of the nut fits into a circular recess in one of the parts connected by the bolt. Through this part passes a set screw D, the point of which can be made to press on the nut at the bottom of the groove C. D is turned back when the nut B is being moved, and when B is tightened up, the set screw is screwed up so as to press hard on the bottom of the groove C. The nut B is thus prevented from slackening back. The screw thread is turned off the set screw at the point where it enters the groove on the nut.

[Illustration: FIG. 19]

The use of the groove for receiving the point of the set screw is this: The point of the set screw indents the nut and raises a bur which would interfere with the free turning of the nut in the recess if the bur was not at the bottom of a groove. Additional security is obtained by drilling a hole through the point of the bolt, and fitting it with a split pin E.

Locking arrangements for nuts are exceedingly numerous, and many of them are very ingenious, but want of space prevents us describing them. We may point out, however, that many very good locking arrangements have the defect of only locking the nut at certain points of a revolution, say at every 30°. It will be noticed that the two arrangements which we have described are not open to this objection.

EXERCISE 18.--Draw, full size, a plan, front elevation, and side elevation of the arrangement of nuts shown in fig. 18, for a bolt 7/8 inch diameter.

EXERCISE 19.--Draw the plan and elevation of the nut and locking arrangement shown in fig. 19. Make also an elevation looking in the direction of the arrow. Scale 6 inches to a foot.

IV. KEYS.

_Keys_ are wedges, generally rectangular in section, but sometimes circular; they are made of wrought iron or steel, and are used for securing wheels, pulleys, cranks, &c., to shafts.

[Illustration: Fig. 20.]

Various sections of keys are shown in fig. 20. At (_a_) is the _hollow_ or _saddle key_. With this form of key it is not necessary to cut the shaft in any way, but its holding power is small, and it is therefore only used for light work. At (_b_) is the _key on a flat_, sometimes called a _flat key_. The holding power of this key is much greater than that of the saddle key. At (_c_) is the _sunk key_, a very secure and very common form.

The part of the shaft upon which a key rests is called the _key bed_ or _key way_, and the recess in the boss of the wheel or pulley into which the key fits is called the _key way_; both are also called _key seats_. With saddle, flat, and sunk keys the key bed is parallel to the axis of the shaft; but the key way is deeper at one end than the other to accommodate the taper of the key. The sides of the key are parallel.

The _round key_ or taper pin shown at (_d_) is in general only used for wheels or cranks which have been previously shrunk on to their shafts or forced on by great pressure. After the wheel or crank has been shrunk on, a hole is drilled, half into the shaft and half into the wheel or crank, to receive the pin.

When the point of a key is inaccessible the other end is provided with a _gib head_ as shown at (_e_), to enable the key to be withdrawn.

A _sliding_ or _feather key_ secures a piece to a shaft so far as to prevent the one from rotating without the other, but allows of relative motion in the direction of the axis of the shaft. This form of key has no taper, and it is secured to the piece carried by the shaft, but is made a _sliding fit_ in the key way of the shaft. In one form of feather key the part within the piece carried by the shaft is dovetailed as shown at (_f_). In another form the key has a round projecting pin forged upon it, which enters a corresponding hole as shown at (_g_). The feather key may also be secured to the piece carried by the shaft by means of one or more screws as shown at (_h_). The key way in the shaft is made long enough to permit of the necessary sliding motion.

_Cone Keys._--These are sometimes fitted to pulleys, and are shown in fig. 32, page 38. In this case the eye of the pulley is tapered and is larger than the shaft. The space between the shaft and the boss of the pulley is filled with three _saddle_ or _cone keys_. These keys are made of cast iron and are all cast together, and before being divided the casting is bored to fit the shaft and turned to fit the eye of the pulley. By this arrangement of keys the same pulley may be fixed on shafts of different diameters by using keys of different thicknesses; also the pulley may be bored out large enough to pass over any boss which may be forged on the shaft.

_Proportions of Keys._--The following rules are taken from Unwin's 'Machine Design,' pp. 142-43.

Diameter of eye of wheel, or boss of shaft = _d_. Width of key = 3/4_d_ + 1/8. Mean thickness of sunk key = 1/8_d_ + 1/8. " key on flat = 1/16_d_ + 1/16.

The following table gives dimensions agreeing with average practice.

_Dimensions of Keys._

D = diameter of shaft. B = breadth of key. T = thickness of sunk key. T_{1} = thickness of flat key, also = thickness of saddle key. Taper of key 1/8 inch per foot of length, _i.e._ 1 in 96.

+---------------------------------------------------------------+ | D | 3/4 | 1 | 1-1/4 | 1-1/2 | 1-3/4 | 2 | 2-1/4 | 2-1/2 | +-----+-----+-----+-------+-------+-------+-----+-------+-------+ | B | 5/16| 3/8 | 7/16 | 1/2 | 9/16 | 5/8 | 11/16 | 11/16 | | T | 1/4 | 1/4 | 1/4 | 5/16 | 5/16 | 5/16| 3/8 | 3/8 | |T_{1}| 3/16| 3/16| 3/16 | 3/16 | 1/4 | 1/4 | 1/4 | 5/16 | +---------------------------------------------------------------+

+-------------------------------------------------------------------+ | D | 2-3/4 | 3 | 3-1/2 | 4 | 4-1/2 | 5 | 5-1/2 | 6 | +-----+-------+-----+-------+-------+-------+-------+-------+-------+ | B | 3/4 | 7/8 | 1 | 1-1/8 | 1-1/4 | 1-3/8 | 1-1/2 | 1-5/8 | | T | 3/8 | 7/16| 1/2 | 1/2 | 9/16 | 5/8 | 11/16 | 3/4 | |T_{1}| 5/16 | 5/16| 3/8 | 7/16 | 1/2 | 1/2 | 9/16 | 5/8 | +-------------------------------------------------------------------+

+-------------------------------------------------------+ | D | 7 | 8 | 9 | 10 | 11 | 12 | +-----+-------+-------+-------+--------+--------+-------+ | B | 1-7/8 | 2-1/8 | 2-3/8 | 2-5/8 | 2-7/8 | 3-1/8 | | T | 13/16 | 15/16 | 1 | 1-1/16 | 1-3/16 | 1-1/4 | |T_{1}| 11/16 | 3/4 | 7/8 | 15/16 | 1-1/16 | 1-1/8 | +-------------------------------------------------------+

V. SHAFTING.

Shafting is nearly always cylindrical and made of wrought iron or steel. Cast iron is rarely used for shafting.

_Axles_ are shafts which are subjected to bending without twisting.

The parts of a shaft or axle which rest upon the bearings or supports are called _journals_, _pivots_, or _collars_.

In journals the supporting pressure is at right angles to the axis of the shaft, while in pivots and collars the pressure is parallel to that axis.

Shafts may be solid or hollow. Hollow shafts are stronger than solid shafts for the same weight of material. Thus a hollow shaft having an external diameter of 10-1/4 inches and an internal diameter of 7 inches would have about the same weight as a solid shaft of the same material 7-1/2 inches in diameter, but the former would have about double the strength of the latter. Hollow shafts are also stiffer and yield less to bending action than solid shafts, which in some cases, as in propeller shafts, is an objection.

VI. SHAFT COUPLINGS.

For convenience of making and handling, shafts used for transmitting power are generally made in lengths not exceeding 30 feet. These lengths are connected by couplings, of which we give several examples.

[Illustration: FIGS. 21 and 22.]

_Solid_, _Box_, or _Muff Couplings._--One form of box coupling is shown in fig. 21. Here the ends of the shafts to be connected butt against one another, meeting at the centre of the box, which is made of cast iron. The shafts are made to rotate as one by being secured to the box by two wrought-iron or steel keys, both driven from the same end of the box. A clearance space is left between the head of the forward key and the point of the hind one, to facilitate the driving of them out, as then only one key needs to be started at a time. Sometimes a single key the whole length of the box is used, in which case it is necessary that the key ways in the shafts be of exactly the same depth.

The half-lap coupling, introduced by Sir William Fairbairn, is shown in fig. 22. In this form of box coupling the ends of the shafts overlap within the box. It is evident that one shaft cannot rotate without the other as long as the box remains over the lap. To keep the box in its place it is fitted with a saddle key.

It will be noticed that the lap joint is sloped in such a way as to prevent the two lengths of shaft from being pulled asunder by forces acting in the direction of their length.

Half-lap couplings are not used for shafts above 5 inches in diameter.

It may here be pointed out that the half-lap coupling is expensive to make, and is now not much used.

As shafts are weakened by cutting key ways in them, very often the ends which carry couplings are enlarged in diameter, as shown in fig. 21, by an amount equal to the thickness of the key. An objection to this enlargement is that wheels and pulleys require either that their bosses be bored out large enough to pass over it, or that they be split into halves, which are bolted together after being placed on the shaft.

_Dimensions of Box Couplings._

D = diameter of shaft. T = thickness of metal in box. L = length of box for butt coupling. L_{1} = length of box for lap coupling. _l_ = length of lap. D_{1} = diameter of shaft at lap.

+---------------------------------------------------------------+ | D | 1-1/2 | 2 | 2-1/2 | 3 | 3-1/2 | 4 | +-------+--------+--------+---------+-------+----------+--------+ | T | 1-1/8 | 1-5/16 | 1-1/2 | 1-3/4 | 1-15/16 | 2-1/8 | | L | 5-3/4 | 7 | 8-1/4 | 9-1/2 | 10-3/4 | 12 | | L_{1} | 4-1/8 | 5-1/4 | 6-3/8 | 7-1/2 | 8-5/8 | 9-3/4 | | _l_ | 1-7/16 | 1-7/8 | 2-5/16 | 2-3/4 | 3-3/16 | 3-5/8 | | D_{2} | 2-5/16 | 3 | 3-11/16 | 4-3/8 | 5-1/16 | 5-3/4 | +---------------------------------------------------------------+

+----------------------------------------------+ | D | 4-1/2 | 5 | 5-1/2 | 6 | +-------+---------+--------+--------+----------+ | T | 2-5/16 | 2-1/2 | 2-3/4 | 2-15/16 | | L | 13-1/4 | 14-1/2 | 15-3/4 | 17 | | L_{1} | 10-7/8 | 12 | -- | -- | | _l_ | 4-1/16 | 4-1/2 | -- | -- | | D_{2} | 6-7/16 | 7-1/8 | -- | -- | +----------------------------------------------+

Slope of lap 1 in 12.

EXERCISE 20: _Solid Butt Coupling._--From the above table of dimensions make a longitudinal and a transverse section of a solid butt coupling for a shaft 2-1/2 inches in diameter. Scale 6 inches to a foot.

EXERCISE 21: _Fairbairn's Half-Lap Coupling._--Make the same views as in the last exercise of a half-lap coupling for a 3-inch shaft to the dimensions in the above table. Scale 6 inches to a foot.

_Flange Couplings._--The form of coupling used for the shafts of marine engines is shown in fig. 23. The ends of the different lengths of shaft have flanges forged on them, which are turned along with the shaft. These flanges butt against one another, and are connected by bolts. These bolts may be parallel or tapered; generally they are tapered. A parallel bolt must have a head, but a tapered bolt will act without one. In fig. 23 the bolts are tapered, and also provided with heads. In fig. 14, page 17, is shown a tapered bolt without a head. The variation of diameter in tapered bolts is 3/8 of an inch per foot of length.

[Illustration: FIG. 23.]

Sometimes a projection is formed on the centre of one flange which fits into a corresponding recess in the centre of the other, for the purpose of ensuring the shafts being in line.

Occasionally a cross-key is fitted in between the flanges, being sunk half into each, for the purpose of diminishing the shearing action on the bolts.

EXERCISE 22: _Marine Coupling._--Draw the elevation and section of the coupling shown in fig. 23; also an elevation looking in the direction of the arrow. Scale 3 inches to a foot.

The following table gives the dimensions of a few marine couplings taken from actual practice.

_Examples of Marine Couplings._

+--------------------------------------------------------------------+ | Diameter of shaft |2-3/8 | 9-3/4 | 12-7/8 |16-1/2 | 22-1/2 | 23 | +--------------------+------+-------+--------+-------+--------+------+ |Diameter of flange | 6 | 19 | 24 | 32 | 35 | 38 | |Thickness of flange | 1 | 2-3/4 | 3-1/8 | 4-1/4 | 6 | 5 | |Diameter of bolts | 3/4 | 2-3/4 | 2-11/16| 3-1/2 | 4-1/4 | 4-1/4| |Number of bolts | 3 | 6 | 6 | 8 | 9 | 8 | |Diameter of bolt | | | | | | | | circle |4-1/8 | 14-1/8|18-13/16| 25 | 28-3/4 |30-3/8| +--------------------------------------------------------------------+

All the above dimensions are in inches.

EXERCISE 23.--Select one of the couplings from the above table, and make the necessary working drawings for it to a suitable scale.

The cast-iron flange coupling is shown in fig. 24. In this kind of coupling a cast-iron centre or boss provided with a flange is secured to the end of each shaft by a sunk key driven from the face of the flange. These flanges are then connected by bolts and nuts as in the marine coupling.

To ensure the shafts being in line the end of one projects into the flange of the other.

In order that the face of each flange may be exactly perpendicular to the axis of the shaft they should be 'faced' in the lathe, after being keyed on to the shaft.

If the coupling is in an exposed position, where the nuts and bolt-heads would be liable to catch the clothes of workmen or an idle driving band which might come in the way, the flanges should be made thicker, and be provided with recesses for the nuts and bolt-heads.

[Illustration: FIG. 24.]

_Dimensions of Cast-iron Flange Couplings._

+--------------------------------------------------------------------+ | |Diameter| | |Depth | |Diameter|Diameter| |Diameter| of |Thickness|Diameter| at |Number| of | of bolt| |of shaft| flange |of flange| of boss| boss | of | bolts | circle | | D | F | T | B | L | bolts| d | C | +--------|--------|---------|--------|------|------|--------|--------+ | 1-1/2 | 7-1/4 | 7/8 | 3-1/2 |2-5/8 | 3 |5/8 | 5-1/2 | | 2 | 8-7/8 | 1-1/16 | 4-3/8 |3-3/16| 4 | 3/4| 6-3/4 | | 2-1/2 | 10-5/8 | 1-1/4 | 5-5/16 |3-3/4 | 4 |7/8 | 8-1/8 | | 3 | 12-3/8 | 1-7/16 | 6-1/4 |4-5/16| 4 | 1 | 9-1/2 | | 3-1/2 | 13-1/8 | 1-5/8 | 7-1/8 |4-7/8 | 4 | 1 |10-5/16 | | 4 | 14 | 1-3/4 | 8 |5-7/16| 6 | 1 |11-1/4 | | 4-1/2 | 15-5/8 | 2 | 8-7/8 |6 | 6 |1-1/8 |12-1/2 | | 5 | 17-3/8 | 2-1/8 | 9-13/16|6-5/8 | 6 | 1-1/4|13-13/16| | 5-1/2 | 18-1/4 | 2-5/16 |10-3/4 |7-1/4 | 6 |1-1/4 |14-3/4 | | 6 | 19-7/8 | 2-1/2 |11-5/8 |7-3/4 | 6 | 1-3/8| 16 | +--------------------------------------------------------------------+

The projection of the shaft _p_ varies from 1/4 inch in the small shafts to 1/2 inch in the large ones.

EXERCISE 24: _Cast-iron Flange Coupling._--Draw the views shown in fig. 24 of a cast-iron flange coupling, for a shaft 4-1/2 inches in diameter, to the dimensions given in the above table. Scale 4 inches to a foot.

VII. BEARINGS FOR SHAFTS.

An example of a very simple form of bearing is shown in fig. 25, which represents a brake shaft carrier of a locomotive tender. The bearing in this example is made of cast iron and in one piece. Through the oval-shaped flange two bolts pass for attaching the bearing to the wrought-iron framing of the tender. With this form of bearing there is no adjustment for wear, so that when it becomes worn it must be renewed.

[Illustration: FIG. 25.]

EXERCISE 25: _Brake Shaft Carrier._--Draw the elevation and sectional plan of the bearing shown in fig. 25. Draw also a vertical section through the axis. The latter view to be projected from the first elevation. Scale 6 inches to a foot.

_Pillow Block_, _Plummer Block_, or _Pedestal_.--The ordinary form of plummer block is represented in fig. 26. A is the block proper, B the sole through which pass the holding-down bolts. C is the cap. Between the block and the cap is the brass bush, which is in halves, called _brasses_ or _steps_. The bed for the steps in this example is cylindrical, and is prepared by the easy process of boring. The steps are not supported throughout their whole length, but at their ends only where fitting strips are provided as shown. As the wear on a step is generally greatest at the bottom, it is made thicker there than at the sides, except where the fitting strips come in. To prevent the steps turning within the block they are generally furnished with lugs, which enter corresponding recesses in the block and cover.

[Illustration: FIG. 26]

In the block illustrated the journal is lubricated by a _needle lubricator_; this consists of an inverted glass bottle fitted with a wood stopper, through a hole in which passes a piece of wire, which has one end in the oil within the bottle, and the other resting on the journal of the shaft. The wire or needle does not fill the hole in the stopper, but if the needle is kept from vibrating the oil does not escape owing to capillary attraction. When, however, the shaft rotates, the needle begins to vibrate, and the oil runs down slowly on to the journal; oil is therefore only used when the shaft is running.

EXERCISE 26: _Pillow Block for a Four-inch Shaft._--Draw the views shown of this block in fig. 26. Make also separate drawings, full size, of one of the steps. Scale 6 inches to a foot.

_Proportions of Pillow Blocks._--The following rules may be used for proportioning pillow blocks for shafts up to 8 inches diameter. It should be remembered that the proportions used by different makers vary considerably, but the following rules represent average practice.

Diameter of journal = _d_. Length of journal = _l_. Height to centre = 1.05_d_ + .5. Length of base = 3.6_d_ + 5. Width of base = .8_l_. " block = .7_l_. Thickness of base = .3_d_ + .3. " cap = .3_d_ + .4. Diameter of bolts = .25_d_ + .25. Distance between centres of cap bolts = 1.6_d_ + 1.5. " " base bolts = 2.7_d_ + 4.2. Thickness of step at bottom = _t_ = .09_d_ + .15. " " sides = 3/4 _t_.

The length of the journal varies very much in different cases, and depends upon the speed of the shaft, the load which it carries, the workmanship of the journal and bearing, and the method of lubrication. For ordinary shafting one rule is to make _l_ = _d_ + 1. Some makers use the rule _l_ = 1.5_d_; others make _l_ = 2_d_.

EXERCISE 27: _Design for Pillow Block._--Make the necessary working drawings for a pillow block for a shaft 5 inches in diameter, and having a journal 7 inches long.

[Illustration: FIG. 27.]

_Brackets._--When a pillow block has to be fixed to a wall or column a bracket such as that shown in figs. 27 and 28 may be used. The pillow block rests between the _joggles_ A A, and is bolted down to the bracket and secured in addition with keys at the ends of the base of the block, in the same manner as is shown, for the attachment of the bracket to the column.

EXERCISE 28: _Pillar Bracket._--Fig. 27 shows a side elevation and part horizontal section, and fig. 28 shows an end elevation of a pillar bracket for carrying a pillow block for a 3-inch shaft. Draw these views _properly projected from one another_, showing the pillow block, which is to be proportioned by the rules given on page 32. Draw also a plan of the whole. Scale 4 inches to a foot.

[Illustration: FIG. 28.]

_Hangers._--When a shaft is suspended from a ceiling it is carried by hangers, one form of which is shown in fig. 29, and which will be readily understood. The cap of the bearing, it will be noticed, is secured by means of a bolt, and also by a square key.

EXERCISE 29: _Shaft Hanger._--Draw the two elevations shown in fig. 29, and also a sectional plan. The section to be taken at a point 5 inches above the centre of the shaft. Scale 6 inches to a foot.

_Wall Boxes._--In passing from one part of a building to another a shaft may have to pass through a wall. In that case a neat appearance is given to the opening and a suitable support obtained for a pillow block by building into the wall a _wall box_, one form of which is shown in fig. 30.

EXERCISE 30: _Wall Box._--Draw the views of the wall box shown in fig. 30, and also a sectional plan; the plane of section to pass through the box a little above the joggles for the pillow block. Scale 3 inches to a foot.

[Illustration: FIG. 29.]

[Illustration: FIG. 30.]

VIII. PULLEYS.

_Velocity Ratio in Belt Gearing._--Let two pulleys A and B be connected by a belt, and let their diameters be D_{1} and D_{2}; and let their speeds, in revolutions per minute, be N_{1} and N_{2} respectively. If there is no slipping, the speeds of the rims of the pulleys will be the same as that of the belt, and will therefore be equal. Now the speed of the rim of A is evidently = D_{1} × 3.1416 × N_{1}; while the speed of the rim of B is = D_{2} × 3.1416 × N_{2}. Hence D_{1} × 3.1416 × N_{1} = D_{2} × 3.1416 × N_{2}, and therefore

N_{1} D_{2} ----- = -----. N_{2} D_{1}

_Pulleys for Flat Bands._--In cross section the rim of a pulley for carrying a flat band is generally curved as shown in figs. 31 and 32, but very often the cross section is straight. The curved cross section of the rim tends to keep the band from coming off as long as the pulley is rotating. Sometimes the rim of the pulley is provided with flanges which keep the band from falling off.

Pulleys are generally made entirely of cast iron, but a great many pulleys are now made in which the centre or nave only is of cast iron, the arms being of wrought iron cast into the nave, while the rim is of wrought sheet iron.

The arms of pulleys when made of wrought iron are invariably straight, but when made of cast iron they are very often curved. In fig. 31, which shows an arrangement of two cast-iron pulleys, the arms are straight; while in fig. 32, which shows another cast-iron pulley, the arms are curved. Through unequal cooling, and therefore unequal contraction of a cast-iron, pulley in the mould, the arms are generally in a state of tension or compression; and if the arms are straight they are very unyielding, so that the result of this initial stress is often the breaking of an arm, or of the rim where it joins an arm. With the curved arm, however, its shape permits it to yield, and thus cause a diminution of the stress due to unequal contraction.

The cross section of the arms of cast-iron pulleys is generally elliptical.

[Illustration: Fig. 31.]

EXERCISE 31: _Fast and Loose Pulleys_.--Fig. 31 shows an arrangement of fast and loose pulleys. A is the fast pulley, secured to the shaft C by a sunk key; B is the loose pulley, which turns freely upon the shaft. The loose pulley is prevented from coming off by a collar D, which is secured to the shaft by a tapered pin as shown. The nave or boss of the loose pulley is here fitted with a brass liner, which may be renewed when it becomes too much worn. Draw the elevations shown, completing the left-hand one. Scale 6 inches to a foot.

By the above arrangement of pulleys a machine may be stopped or set in motion at pleasure. When the driving band is on the loose pulley the machine is at rest, and when it is on the fast pulley the machine is in motion. The driving band is shifted from the one pulley to the other by pressing on that side of the band which is advancing towards the pulleys.

[Illustration: FIG. 32.]

EXERCISE 32: _Cast-iron Pulley with Curved Arms and Cone Keys_.--Draw a complete side elevation and a complete cross section of the pulley represented in fig. 32 to a scale of 3 inches to a foot. In drawing the side elevation of the arms first draw the centre lines as shown; next draw three circles for each arm, one at each end and one in the middle; the centres of these circles being on the centre line of the arm, and their diameters equal to the widths of the arm at the ends and at the middle respectively. Arcs of circles are then drawn to touch these three circles. The centres and radii of these arcs may be found by trial. The cone keys for securing the pulley to the shaft were described on p. 23.

_Pulleys for Ropes_.--Ropes made of hemp are now extensively used for transmitting power. These ropes vary in diameter from 1 inch to 2 inches, and are run at a speed of about 4,500 feet per minute. The pulleys for these ropes are made of cast iron, and have their rims grooved as shown in fig. 33, which is a cross section of the rim of a pulley carrying three ropes. The angle of the V is usually 45°, and the rope rests on the sides of the groove, and not on the bottom, so that it is wedged in, and has therefore a good hold of the pulley. The diameter of the pulley should not be less than 30 times the diameter of the rope. Two pulleys connected by ropes should not be less than thirty feet apart from centre to centre, but this distance may be as much as 100 feet.

[Illustration: FIG. 33.]

EXERCISE 33: _Section of Rim of Rope Pulley._--Draw, half size, the section of the rim of a rope pulley shown in fig. 33.

IX. TOOTHED WHEELS.

_Pitch Surfaces of Spur Wheels._--Let two smooth rollers be placed in contact with their axes parallel, and let one of them rotate about its axis; then if there is no slipping the other roller will rotate in the opposite direction with the same surface velocity; and if D_{1}, D_{2} be the diameters of the rollers, and N_{1}, N_{2} their speeds in revolutions per minute, it follows as in belt gearing that--

N_{1} D_{2} ----- = -----. N_{2} D_{1}

If there be considerable resistance to the motion of the follower slipping may take place, and it may stop. To prevent this the rollers may be provided with teeth; then they become _spur wheels_; and if the teeth be so shaped that the ratio of the speeds of the toothed rollers at any instant is the same as that of the smooth rollers, the surfaces of the latter are called the _pitch surfaces_ of the former.

_Pitch Circle._--A section of the pitch surface of a toothed wheel by a plane perpendicular to its axis is a circle, and is called a _pitch circle_. We may also say that the pitch circle is the edge of the pitch surface. The pitch circle is generally traced on the side of a toothed wheel, and is rather nearer the points of the teeth than the roots.

_Pitch of Teeth._--The distance from the centre of one tooth to the centre of the next, or from the front of one to the front of the next, _measured at the pitch circle_, is called the _pitch of the teeth_. If D be the diameter of the pitch circle of a wheel, _n_ the number of teeth, and _p_ the pitch of the teeth, then D × 3.1416 = _n_ × _p_.

[Illustration: FIG. 34.]

By the diameter of a wheel is meant the diameter of its pitch circle.

_Form and Proportions of Teeth._--The ordinary form of wheel teeth is shown in fig. 34. The curves of the teeth should be cycloidal curves, although they are generally drawn in as arcs of circles. It does not fall within the scope of this work to discuss the correct forms of wheel teeth. The student will find the theory of the teeth of wheels clearly and fully explained in Goodeve's 'Elements of Mechanism,' and in Unwin's 'Machine Design.'

The following proportions for the teeth of ordinary toothed wheels may be taken as representing average practice:--

Pitch of teeth = _p_ = arc _a b c_ (fig. 34). Thickness of tooth = _b c_ = .48_p_. Width of space = _a b_ = .52_p_. Total height of tooth = _h_ = .7_p_. Height of tooth above pitch line = _k_ = .3_p_. Depth of tooth below pitch line = _l_ = .4_p_. Width of tooth = 2_p_ to 3_p_.

EXERCISE 34: _Spur Wheel._--Fig. 35 shows the elevation and sectional plan of a portion of a cast-iron spur wheel. The diameter of the pitch circle is 23-7/8 inches, and the pitch of the teeth is 1-1/2 inches, so that there will be 50 teeth in the wheel. The wheel has six arms. Draw a complete elevation of the wheel and a half sectional plan, also a half-plan without any section. Draw also a cross section of one arm. Scale 4 inches to a foot.

[Illustration: FIG. 35.]

_Mortise Wheels._--When two wheels gearing together run at a high speed the teeth of one are made of wood. These teeth, or cogs, as they are generally called, have tenons formed on them, which fit into mortises in the rim of the wheel. This wheel with the wooden teeth is called a _mortise wheel_. An example of a mortise wheel is shown in fig. 36.

[Illustration: FIG. 36.]

_Bevil Wheels._--In bevil wheels the pitch surfaces are parts of cones. Bevil wheels are used to connect shafts which are inclined to one another, whereas spur wheels are used to connect parallel shafts. In fig. 36 is shown a pair of bevil wheels in gear, one of them being a mortise wheel. At (_a_) is a separate drawing, to a smaller scale, of the pitch cones. The pitch cones are shown on the drawing of the complete wheels by dotted lines.

The diameters of bevil wheels are the diameters of the bases of their pitch cones.

EXERCISE 35: _Pair of Bevil Wheels._--Draw the sectional elevation of the bevil wheels shown in gear in fig. 36. Commence by drawing the centre lines of the shafts, which in this example are at right angles to one another; then draw the pitch cones shown by dotted lines. Next put in the teeth which come into the plane of the section, then complete the sections of the wheels. The pinion or smaller wheel has 25 teeth, and the wheel has 50 teeth, which makes the pitch a little over 3 inches. Each tooth of the mortise wheel is secured as shown by an iron pin 5/16 inch diameter. Scale 3 inches to a foot.

X. CRANKS AND CRANKED SHAFTS.

The most important application of the crank is in the steam-engine, where the reciprocating rectilineal motion of the piston is converted into the rotary motion of the crank-shaft by means of the crank and connecting rod.

At one time steam-engine cranks were largely made of cast iron, now they are always made of wrought iron or steel. The crank is either forged in one piece with the shaft, or it is made separately and then keyed to it.

_Overhung Crank._--Fig. 37 shows a wrought-iron overhung crank. A is the crank-shaft, B the crank arm, provided at one end with a boss C, which is bored out to fit the shaft; at the other end of the crank arm is a boss D, which is bored out to receive the crank-pin E, which works in one end of the connecting rod. The crank is secured to the shaft by the sunk key F. It is also good practice to _shrink_ the crank on to the shaft. The process of shrinking consists of boring out the crank a little smaller than the shaft, and then heating it, which causes it to expand sufficiently to go on to the shaft. As the crank cools, it shrinks and grips the shaft firmly. The crank may also be shrunk on to the crank-pin, the latter being then riveted over as shown in fig. 37.

[Illustration: FIG. 37.]

A good plan to adopt in preference to the shrinking process is to force the parts together by hydraulic pressure. This method is adopted for placing locomotive wheels on their axles, and for putting in crank-pins. As to the amount of pressure to be used, the practice is to allow a force of 10 tons for every inch of diameter of the pin, axle, or shaft.

Instead of being riveted in, the crank pin may be prolonged and screwed, and fitted with a nut. Another plan is to put a cotter through the crank and the crank-pin.

The distance from the centre of the crank-shaft to the centre of the crank-pin is called the radius of the crank. The _throw_ of the crank is twice the radius. In a direct-acting engine the throw of the crank is equal to the stroke of the piston.

EXERCISE 36: _Wrought-iron Overhung Crank._--Draw the two elevations shown in fig. 37, also a plan. Scale 1-1/2 inches to a foot.

_Proportions of Overhung Cranks._

D = diameter of shaft. _d_ = " crank-pin. Length of large boss = .9 D. Diameter " = 1.8 D. Length of small boss = 1.1 _d_. Diameter " = 1.8 _d_. Width of crank arm at centre of shaft = 1.3 D. " " crank-pin = 1.5 _d_. The thickness of the crank arm may be roughly taken as = .7 D.

EXERCISE 37.--Design a wrought-iron crank for an engine having a stroke of 4 feet. The crank-shaft is 9 inches in diameter, and the crank-pin is 4-3/4 inches in diameter and 6-1/2 inches long.

[Illustration: FIG. 38.]

_Locomotive Cranked Axle._--As an example of a cranked shaft we take the cranked axle for a locomotive with inside cylinders shown in fig. 38; here the crank and shaft or axle are forged in one piece. A is the wheel seat, B the journal, C the crank-pin, and D and E the crank arms. Only one half of the axle is shown in fig. 38, but the other half is exactly the same. The cranks on the two halves are, however, at right angles to one another. The ends of the crank arms are turned in the lathe, the crank-pin ends being turned at the same time as the axle, and the other ends at the same time as the crank-pin. This consideration determines the centres for the arcs shown in the end view.

EXERCISE 38.--Draw to a scale of 2 inches to a foot the side and end elevations of the locomotive cranked axle partly shown in fig. 38. The distance between the centre lines of the cylinders is 2 feet.

[Illustration: FIG. 39.]

_Built-up Cranks._--The form of cranked shaft shown in fig. 38 is largely used for marine engines, but for the very powerful engines now fitted in large ships this design of shaft is very unreliable, the built-up crank shown in fig. 39 being preferred, although it is much heavier than the other. It will be seen from the figure that the shaft, crank arms, and crank-pin are made separately. The arms are shrunk on to the pin and the shaft, and secured to the latter by sunk keys. These heavy shafts and cranks are generally made of steel.

EXERCISE 39.--Keeping to the dimensions marked in fig. 39, draw the views there shown of a built-up crank-shaft for a marine engine. Scale 3/4 inch to a foot.

XI. ECCENTRICS.

The _eccentric_ is a particular form of crank, being a crank in which the crank-pin is large enough to embrace the crank-shaft. In the eccentric what corresponds to the crank-pin is called the sheave or pulley. The advantage which an eccentric possesses over a crank is that the shaft does not require to be divided at the point where the eccentric is put on. The crank, however, has this advantage over the eccentric, namely, that it can be used for converting circular into reciprocating motion, or _vice versâ_, while the eccentric can only be used for converting circular into reciprocating motion. This is owing to the great leverage at which the friction of the eccentric acts.

The chief application of the eccentric is in the steam-engine, where it is used for working the valve gear.

To permit of the sheave being placed on the shaft without going over the end (which could not be done at all in the case of a cranked axle, and would be a troublesome operation in most cases) it is generally made in two pieces, as shown in fig. 40, which represents one of the eccentrics of a locomotive. The two parts of the sheave are connected by two cotter bolts. The part which embraces the sheave is called the eccentric strap, and corresponds to, and is, in fact, a connecting rod end: the rod proceeding from this is called the eccentric rod.

The distance from the centre of the sheave to the centre of the shaft is called the _radius_ or _eccentricity_ of the eccentric. The _throw_ is twice the eccentricity.

The sheave is generally made of cast iron. The strap may be of brass, cast iron, or wrought iron; when the strap is made of wrought iron it is commonly lined with brass.

[Illustration: FIG. 40.]

EXERCISE 40: _Locomotive Eccentric._--In fig. 40 D E is the sheave, F H the strap, and K the eccentric rod. The sheave and strap are made of cast iron, and the eccentric rod is made of wrought iron. (_a_) is a vertical cross section through the oil-box of the strap; (_b_) is a plan of the end of the eccentric rod and part of the strap. All the nuts are locked by means of cotters. Draw first the elevation, partly in section as shown. Next draw two end elevations, one looking each way. Afterwards draw a horizontal section through the centre, and also a plan. Scale 4 inches to a foot.

XII. CONNECTING RODS.

The most familiar example of the use of a connecting rod is in the steam-engine, where it is used to connect the rotating crank with the reciprocating piston. The rod itself is made of wrought iron or steel, and is generally circular or rectangular in section. The ends of the rod are fitted with steps, which are held together in a variety of ways.

_Strap End._--A form of connecting rod end, which is not so common as it used to be, is shown in fig. 41. At (_a_) is shown a longitudinal section with all the parts put together, while at (_b_), (_c_), _(d)_ and (_e_) the details are shown separately. A B is the end of the rod which butts against the brass bush C D, which is in two pieces. A _strap_ E passes round the bush and on to the end of the rod as shown. The arms of the strap have rectangular holes in them, which are not quite opposite a similar hole in the rod when the parts are put together. If a wedge or _cotter_ F be driven into these three holes they will tend to come into line, and the parts of the bush will be pressed together. To prevent the cotter opening out the strap, and to increase the sliding surface, a _gib_ H is introduced. The gib is provided with horns at its ends to keep it in its place. Sometimes two gibs are used, one on each side of the cotter; this makes the sliding surface on both sides of the cotter the same. The cotter is secured by a set screw K. The unsectioned portion of fig. (_a_) to the right of the gib, or to the left of the cotter, is called the _clearance_ or _draught._

[Illustration: FIG. 41.]

EXERCISE 41: _Connecting Rod End._--Make the following views of the connecting rod end illustrated by fig. 41. First, a vertical section, the same as shown at (_a_). Second, a horizontal section. Third, side elevation. Fourth, a plan. Or the first and third views may be combined in a half vertical section and half elevation; and the second and fourth views may be combined in a half horizontal section and half plan.

All the dimensions are to be taken from the detail drawings (_b_), (_c_), (_d_), and (_e_), _but the details need not be drawn separately_. The brass bush is shown at (_d_) by half elevation, half vertical section, half plan, and half horizontal section. The draught or clearance is 7-16ths of an inch.

_Box End._--At (_a_), fig. 42, is shown what is known as a box end for a connecting rod. The part which corresponds to the loose strap in the last example is here forged in one piece with the connecting rod. In this form the brass bush is provided with a flange all round on one side, but on the opposite side the flange is omitted except at one end; this is to allow of the bush being placed within the end of the rod. The construction of the bush will be understood by reference to the sketch shown at (_b_). The bush is in two parts, which are pressed tightly together by means of a cotter. This cotter is prevented from slackening back by two set screws. Each set screw is cut off square at the point, and presses on the flat bottom of a very shallow groove cut on the side of the cotter.

The top, bottom, and ends of this box end are turned in the lathe at the same time as the rod itself; this accounts for the curved sections of these parts.

It is clear from the construction of a box end that it is only suitable for an overhung crank.

EXERCISE 42: _Locomotive Connecting Rod._--In fig. 42 is shown a connecting rod for an outside cylinder locomotive. (_a_) is the crank-pin end, and (_c_) the cross-head end. The end (_a_) has just been described under the head 'box end.' We may just add that in this particular example the brass bush is lined with white metal as shown, and that the construction of the oil-box is the same as that on the coupling rod end shown in fig. 44. The end (_c_) is forked, and through the prongs of the fork passes the cross-head pin, of which a separate dimensioned drawing is shown at (_d_). Observe that the tapered parts A and B of this pin are parts of the same cone. The rotation of the pin is prevented by a small key as shown. The cross-head pin need not be drawn separately, and the isometric projection of the bush at (_b_) may be omitted, but all the other views shown are to be drawn to a scale of 6 inches to a foot.

_Marine Connecting Rod._--The form of connecting rod shown in fig. 43 is that used in marine engines, but it is also used extensively in land engines. A B is the crank-pin end, and C the cross-head end. The end A B is forged in one piece, and after it is turned, planed, and bored it is slotted across, so as to cut off the cap A. The parts A and B are held together by two bolts as shown. This end of the rod is fitted with brass steps, which are lined with white metal. The cross-head end is forked, and through the prongs of the fork passes a pin D, which also passes through the cross-head, which is forged on to the piston rod or attached to it in some other way.

[Illustration: FIG. 42.]

[Illustration: FIG. 43.]

EXERCISE 43: _Marine Connecting Rod._--Draw all the views shown in fig. 43 of one form of marine connecting rod. For detail drawings of the locking arrangement for the nuts see fig. 19, page 21. Scale 4 inches to a foot.

_Coupling Rods._--A rod used to transmit the motion of one crank to another is called a _coupling rod_. A familiar example of the use of coupling rods will be found in the locomotive. Coupling rods are made of wrought iron or steel, and are generally of rectangular section. The ends are now generally made solid and lined with solid brass bushes, _without any adjustment for wear_. This form of coupling rod end is found to answer very well in locomotive practice where the workmanship and arrangements for lubrication are excellent. When the brass bush becomes worn it is replaced by a new one.

Fig. 44 shows an example of a locomotive coupling rod end for an outside cylinder engine. In this case it is desirable to have the crank-pin bearings for the coupling rods as short as possible, for a connecting rod and coupling rod in this kind of engine work side by side on the same crank-pin, which, being overhung, should be as short as convenient for the sake of strength. The requisite bearing surface is obtained by having a pin of large diameter. The brass bush is prevented from rotating by means of the square key shown. The oil-box is cut out of the solid, and has a wrought-iron cover slightly dovetailed at the edges. This cover fits into a check round the top inner edge of the box, which is originally parallel, but is made to close on the dovetailed edges of the cover by riveting. A hole in the centre of this cover, which gives access to the oil-box, is fitted with a screwed brass plug. The brass plug has a screwed hole in the centre, through which oil may be introduced to the box. Dust is kept out of the oil-box by screwing into the hole in the brass plug a common cork. The oil is carried slowly but regularly from the oil-box over to the bearing by a piece of cotton wick.

[Illustration: FIG. 44.]

EXERCISE 44: _Coupling Rod End._--Draw first the side elevation and plan, each partly in section as shown in fig. 44. Then instead of the view to the left, which is an end elevation partly in section, draw a complete end elevation looking to the right, and also a complete vertical cross section through the centre of the bearing. Scale 6 inches to a foot.

XIII. CROSS-HEADS.

An example of a steam-engine cross-head is shown in fig. 45. A is the end of the piston rod which has forged upon it the cross-head B. The cross-head pin shown at (_d_), fig. 42, and to which the connecting rod is attached, works in the bearing C. Projecting pieces D, forged on the top and bottom of the cross-head, carry the slide blocks E which work on the slide bars, and thus guide the motion of the piston rod.

[Illustration: FIG. 45.]

EXERCISE 45: _Locomotive Cross-head._--In fig. 45 are shown side and end elevations, partly in section, of the cross-head and slide blocks for an outside cylinder locomotive. Draw these views half size, showing also on the end elevation the cross-head pin and a vertical section of the connecting rod end from fig. 42. The bush in the cross-head which forms the bearing for the cross-head pin is of wrought iron, case-hardened, and is prevented from rotating by the key shown. The cross-head is of wrought iron, and the slide blocks are of cast iron, and are fitted with white metal strips as shown. A short brass tube leads oil from the upper slide block into a hole in the cross-head as shown, which carries it to a slot in the bush which distributes it over the cross-head pin.

XIV. PISTONS.

A _piston_ is generally a cylindrical piece which slides backwards and forwards inside a hollow cylinder. The piston may be moved by the action of fluid pressure upon it as in a steam-engine, or it may be used to give motion to a fluid as in a pump.

A piston is usually attached to a rod, called a _piston rod_, which passes through the end of the cylinder inside which the piston works, and which serves to transmit the motion of the piston to some piece outside the cylinder, or _vice versâ_.

[Illustration: FIG. 46.]

A _plunger_ is a piston made in one piece with its piston rod, the piston and the rod being of the same diameter.

A piston which is provided with one or more valves which allow the fluid to pass through it from one side to the other is called a _bucket_.

_Simple Piston._--The simplest form of piston is a plain cylinder fitting accurately another, inside which it moves. Such a piston works with very little friction, but as there is no adjustment for wear, such a piston is not suitable for a high fluid pressure if it has to work constantly. This simple form of piston is used in the steam-engine indicator, and also in pumps.

Fig. 46 shows the piston of the circulation pump of a marine engine. A is the cast-iron casing or barrel of the pump; B is a brass liner fitting tightly into the former at its ends, and secured by eight screwed Muntz metal pins C, four at each end; D is the piston, which is made of brass, and is attached to a Muntz metal piston rod E. The liner is bored out smooth and true from end to end, and the piston is turned so as to be a sliding fit to the liner. The wear in this form of piston is diminished by making the rubbing surface large.

EXERCISE 46: _Piston for Circulating Pump._--Draw the vertical sectional elevation of the piston, &c., shown in fig. 46, also a half plan and half horizontal section through the centre. Scale 4 inches to a foot.

_Pump Bucket._--The next form of piston which we illustrate is shown in fig. 47. This represents the air-pump bucket of a marine engine. The bucket is made of brass, and is provided with six india-rubber disc valves. The rod is in this case made of Muntz metal. Air-pump rods for marine engines are very often made of wrought iron cased with brass. It will be observed that there is a wide groove around the bucket, which is filled with hempen rope or gasket. This gasket forms an elastic packing which prevents leakage. This is an old-fashioned form of packing, and is now only used for pump buckets.

[Illustration: FIG. 47.]

EXERCISE 47: _Air-pump Bucket._--Draw the sectional elevation of the air-pump bucket shown in fig. 47. Also draw a half plan looking downwards and a half plan looking upwards. Scale 4 inches to a foot.

_Ramsbottom's Packing._--The form of packing used in the air-pump bucket, fig. 47, is not suitable for steam pistons. For the latter the packing is now always metallic. The simplest form of metallic packing is that known as Ramsbottom's. This form is very largely used for locomotive pistons, and for small pistons in many kinds of engines besides. A locomotive piston for an 18-inch cylinder with Ramsbottom's packing is shown in fig. 48. The particular piston there illustrated is made of brass, and is secured to a wrought-iron piston rod by a brass nut. Two circumferential grooves of rectangular section are turned out of the piston, and into these fit two corresponding rings, which may be of brass, cast iron, or steel. In this example the rings are of cast iron. These rings are first turned a little larger in diameter than the bore of the cylinder (in this example 1/2 inch), and then sprung over the piston into the groves prepared for them. Their own elasticity causes the rings to press outwards on the cylinder. At the point where a ring is split a leakage of steam will take place, but with quick-running pistons this leakage is unimportant. The points where the rings are cut should be placed diametrically opposite, so as to diminish the leakage of steam.

[Illustration: FIG. 48.]

EXERCISE 48: _Locomotive Piston._--A part elevation and part section of a locomotive piston, for a cylinder having a bore 18 inches in diameter, is shown in fig. 48. Draw this, and also a view looking on the nut in the direction of the axis of the piston rod. Scale 6 inches to a foot.

_Note._--The reason why the part of the piston rod within the piston has such a quick taper is that the piston has to be taken off the rod while it is in the cylinder. The cross-head being forged on the end of the piston rod prevents the piston and piston rod being withdrawn together.

_Large Pistons._--Pistons of large diameter are generally provided with two cast-iron packing rings placed within the same groove. These rings are pressed outwards against the cylinder, and also against the sides of the groove by one or more springs. One form of this packing (Lancaster's) is shown in fig. 49. Here one spring only is used, and it is first made a straight spiral spring, and then bent round and its ends united. The action of the spring will be clearly understood from the illustration. For the purpose of admitting the packing rings the piston is divided into two parts, one the piston proper, and the other the _junk ring_. In fig. 49, A is the junk ring, which is secured to the piston by means of bolts as shown.

[Illustration: FIG. 49.]

EXERCISE 49: _Marine Engine Piston._--The piston illustrated by fig. 49 is for the high-pressure cylinder of a marine engine. The piston, junk ring, and packing rings are of cast iron. The piston rod and nut are of wrought iron, so also are the junk ring bolts. The nuts for the latter are of brass. The spiral spring is made from steel wire 3/8 inch diameter. An enlarged section of one of the packing rings is shown at (_a_). A front elevation of the locking arrangement for the piston rod nut is shown at (_b_). A sectional plan of one of the nuts for the junk ring bolts is shown at (_c_).

First draw the vertical section of this piston, next draw a plan, one-third of which is to show the piston complete, one-third to show the junk ring removed, and the remaining third to be a horizontal section through between the packing rings. The details (_a_) and (_c_) need not be drawn separately. Scale 3 inches to a foot.

_Proportions of Marine Engine Pistons._--Mr. Seaton, in his 'Manual of Marine Engineering,' gives the following rules for designing marine engine pistons:--

D = diameter of piston in inches. _p_ = effective pressure in lbs. per square inch. _x_ = D/50 × [sqrt (_p_)] + 1.

Thickness of front of piston near boss 0.2 × _x_. " " " rim 0.17 × _x_. " back of piston 0.18 × _x_. " boss around rod 0.3 × _x_. " flange inside packing ring 0.23 × _x_. " " at edge 0.25 × _x_. " junk ring at edge 0.23 × _x_. " " inside packing ring. 0.21 × _x_. " " at bolt-holes 0.35 × _x_. " metal around piston edge 0.25 × _x_. Breadth of packing ring 0.63 × _x_. Depth of piston at centre 1.4 × _x_. Lap of junk ring on piston 0.45 × _x_. Space between piston body and packing ring 0.3 × _x_. Diameter of junk-ring bolts 0.1 × _x_ + .25 inch. Pitch of junk-ring bolts 10 diameters. Number of webs in piston (D + 20)/12. Thickness " 0.18 × _x_.

EXERCISE 50: _Design for Marine Engine Piston._--Calculate by Seaton's rules the dimensions for a marine engine piston 40 inches in diameter, and subjected to an effective pressure of 36 lbs. per square inch. Then make the necessary working drawings for this piston to a scale of, say, 3 inches to a foot.

_Note._--Take the dimensions got by calculation to the nearest 1-16th of an inch.

XV. STUFFING-BOXES.

[Illustration: FIG. 50.]

In fig. 50 is shown a gland and stuffing-box for the piston rod of a vertical engine. A B is the piston rod, C D a portion of the cylinder cover, and E F the _stuffing-box_. Fitting into the bottom of the stuffing-box is a brass bush H. The space K around the rod A B is filled with _packing_, of which there is a variety of kinds, the simplest being greased hempen rope. The packing is compressed by screwing down the cast-iron gland L M, which is lined with a brass bush N. In this case the gland is screwed down by means of three stud-bolts P, which are screwed into a flange cast on the stuffing-box. Surrounding the rod on the top of the gland there is a recess R for holding the lubricant.

[Illustration: FIG. 51.]

[Illustration: FIG. 52.]

The object of the gland and stuffing-box is to allow the piston rod to move backwards and forwards freely without any leakage of steam.

Fig. 51 shows a gland and stuffing-box for a horizontal rod. The essential difference between this example and the last is in the mode of lubrication. The gland flange has cast within it an oil-box which is covered by a lid; this lid is kept shut or open by the action of a small spring as shown. A piece of cotton wick (not shown in the figure) has one end trailing in the oil in the oil-box, while the other is carried over and passed down the hole A B. The wick acts as a siphon, and drops the oil gradually on to the rod. In this example only two bolts are used for screwing in the gland; and the flanges of the gland and stuffing-box are not circular, but oval-shaped.

In the case of small rods the gland is made entirely of brass, and no liner is then necessary. Fig. 52 shows a form of gland and stuffing-box sometimes used for small rods. The stuffing-box is screwed externally, and carries a nut A B which moves the gland.

EXERCISE 51: _Gland and Stuffing-box for a Vertical Rod._--Draw the views shown in fig. 50 to the dimensions given. Scale 6 inches to a foot.

EXERCISE 52: _Gland and Stuffing-box for a Horizontal Rod._--Fig. 51 shows a plan, half in section, and an elevation half of which is a section through the gland flange. Draw these to a scale of 6 inches to a foot, using the dimensions marked in the figure.

EXERCISE 53: _Screwed Gland and Stuffing-box._--Draw, full size, the views shown in fig. 52 to the given dimensions.

A more elaborate form of gland and stuffing-box is shown in fig. 53. This is for a large marine engine with inverted cylinders, such as is used on board large ocean steamers. The stuffing-box is cast separate from the cylinder cover to which it is afterwards bolted. The lubricant is first introduced to the oil-boxes marked A, from which it passes to the recess B, where it comes in contact with the piston rod. To prevent the lubricant from being wasted by running down the rod, the main gland is provided with a shallow gland and stuffing-box which is filled with soft cotton packing, which soaks up the lubricant.

The main gland is screwed up by means of six bolts, and to prevent the gland from locking itself in the stuffing-box, it is necessary that the nuts should be turned together. This is done in a simple and ingenious manner. One-half of each nut is provided with teeth, and these gear with a toothed wheel which has a rim only; this rim is held up by a ring C. When one nut is turned, all the rest follow in the same direction.

[Illustration: FIG. 53.]

EXERCISE 54: _Gland and Stuffing-box for Piston Rod of Large Inverted Cylinder Engine._--The lower view in fig. 53 is a half plan looking upwards, and a half section of the gland looking downwards. The upper view is a vertical section. Complete all these views and add an elevation. Scale 3 inches to a foot.

_Note._--The large nuts, the wheel, the supporting ring, and small gland are made of brass.

_Dimensions of Stuffing-boxes and Glands._

_d_ = diameter of rod. _t__{1} = thickness of _d__{1} = diameter of box (inside). stuffing-box flange. _l_ = length of stuffing-box _t__{2} = thickness of gland bush. flange. _l__{1} = length of packing space. _t__{3} = thickness of bushes in _l__{2} = length of gland. box and gland. _t_ = thickness of metal in _d__{2} = diameter of gland bolts. stuffing-box. _n_ = number of bolts.

+----------------------------------------------------------+ | _d_ | _d__{1} | _l_ | _l__{1} | _l__{2} | _t_ | _t__{1} | +-----+---------+-----+---------+---------+------+---------+ |1 | 1-3/4 | 3/4| 2 | 1-1/2 | 7/16| 1/2 | |1-1/2| 2-1/2 |1-1/4| 2-5/8 | 2 | 9/16| 11/16 | |2 | 3-1/2 |1-3/4| 3-1/4 | 2-1/2 | 11/16| 7/8 | |2-1/2| 4-1/8 |2-1/4| 3-7/8 | 2-7/8 | 13/16| 1-1/16 | |3 | 4-3/4 |2-3/4| 4-1/2 | 3-1/4 | 15/16| 1-1/4 | |3-1/2| 5-1/4 | 3 | 5-1/8 | 3-5/8 |1 | 1-3/8 | |4 | 5-7/8 |3-1/4| 5-3/4 | 4 |1 | 1-3/8 | |4-1/2| 6-3/8 |3-1/2| 6-3/8 | 4-3/8 |1-1/16| 1-9/16 | |5 | 7 |3-3/4| 7 | 4-5/8 |1-1/16| 1-9/16 | |6 | 8 |4-1/4| 8-1/4 | 5 |1-1/8 | 1-11/16 | +----------------------------------------------------------+

+-------------------------------------------------+ | _d_ | _t__{2} | _t__{3} | _d__{2} | _n_ | +-----+-----------------+---------+---------+-----+ |1 | _t__{2}=_t_ | 3/16 | 7/16 | 2 | |1-1/2| when gland | 1/4 | 5/8 | 2 | |2 | flange is | 5/16 | 3/4 | 2 | |2-1/2| made of cast | 5/16 | 7/8 | 2 | |3 | iron and | 3/8 | 1 | 2 | |3-1/2| _t__{2}=_t__{1} | 3/8 | 1 | 2 | |4 | when gland | 7/16 | 1 | 2 | |4-1/2| flange is | 7/16 | 7/8 | 4 | |5 | made of | 7/16 | 1 | 4 | |6 | brass. | 1/2 | 1-1/4 | 4 | +-------------------------------------------------+

The proportions of glands and stuffing-boxes vary considerably but the above table represents average practice.

EXERCISE 55:--Make the necessary working drawings for a gland and stuffing-box for a locomotive engine piston rod 2-1/2 inches in diameter, to the dimensions given in the table.

XVI. VALVES.

Professor Unwin divides valves, according to their construction into three classes as follows:--(1) flap valves, which bond or turn upon a hinge; (2) lift valves, which rise perpendicularly to the seat; (3) sliding valves, which move parallel to the seat.

Examples of flap valves are shown in figs. 54 and 55; two forms of lift valves are shown in figs. 56 and 57, and in figs. 58 and 59 are shown two forms of slide valve. The slide valve shown in fig. 58 moves in a straight line, while that shown in fig. 59 (called a cock) moves in circle.

_India-rubber Valves._--In india-rubber valves there is a grating covered by a piece of india-rubber, which may be rectangular, but is generally circular, and which is held down along one edge if rectangular, or at the centre if circular. Water or other fluid can pass freely upwards through the grating, but when it attempts to return the elasticity of the india-rubber, and the pressure of the water upon it, cause it to lie close on the grating, and thus prevent the return of the water. The india-rubber is prevented from rising too high by a perforated guard. In fig. 54 is shown an example of an india-rubber disc valve. A is the grating, B the india-rubber, C the guard secured to the grating or seat by the stud D and nut E. The grating is held in position by bolts and nuts F. The grating and guard are generally of brass.

India-rubber disc valves are also shown on the air-pump bucket, fig. 47.

EXERCISE 56: _India-rubber Disc Valve._--Fig. 54 shows a vertical section and a plan of an india-rubber disc valve. In the plan one-half of the guard and india-rubber are supposed to be removed so as to show the grating or seat. Draw these views, and also an elevation. A detail drawing of the central stud is shown in fig. 16, page 18. In fig. 54 the elevation of the guard is drawn as it is usually drawn in practice, but if the student has a sufficient knowledge of descriptive geometry he should draw the elevation completely showing the perforations. Scale 6 inches to a foot.

[Illustration: FIG. 54.]

[Illustration: FIG. 55.]

_Kinghorn's Metallic Valve._--The action of this valve is the same as that of an india-rubber valve, but a thin sheet of metal (phosphor bronze) takes the place of the india-rubber.

This valve is now largely used in the pumps of marine engines, and is shown in fig. 55 as applied to an air-pump bucket. Three valves like the one shown are arranged round the bucket.

EXERCISE 57: _Kinghorn's Metallic Valve._--Fig. 55 shows an elevation and plan of one form of this valve. In the plan one-half of the guard and metal sheet are supposed to be removed, so as to show the grating, which in this case is part of an air-pump bucket. Draw the views shown, and also a vertical section of the guard through the centres of the bolts. All the parts are of brass except the valve proper, which is of phosphor bronze. Scale 6 inches to a foot.

_Conical Disc Valves._--A very common form of valve is that shown in figs. 56 and 57. This form of valve consists of a disc, the edge of which (called the face) is conical. The conical edge of this disc fits accurately on a corresponding seat. The angle which the valve face makes with its axis is generally 45°. If the disc is raised, either by the action of the fluid as in the india-rubber valve, or by other means, an opening is formed around the disc through which the fluid can pass. The valve is guided in rising and falling either by three feathers underneath it, as in fig. 56, or by a central spindle which moves freely through a hole in the centre of a bridge which stretches across the seat, as in fig. 57. The lift of the valve is limited by a stop above it, which forms part of the casing containing the valve. The lift should in no case exceed one-fourth of the diameter of the valve, and it is generally much less than this. The guiding feathers (fig. 56) are notched immediately under the disc for the purpose of making available the full circumferential opening of the valve for the passage of the fluid. These notches also prevent the feathers from interfering with the turning or scraping of the valve face.

Conical disc valves and their seats are nearly always made of brass.

EXERCISE 58: _Conical Disc Valves._--Draw, half size, the plans and elevations shown in figs. 56 and 57. In fig. 57 the valve is shown open in the elevation, and in the plan it is removed altogether in order to show the seat with its guide bridge.

[Illustration: Plan of Valve. FIG. 56.]

[Illustration: Plan of Seat. FIG. 57.]

_Simple Slide Valve._--The form of valve shown in fig. 58, often called the _locomotive slide valve_, is very largely used in all classes of steam-engines for distributing the steam in the steam cylinders. The valve is shown separately at (_d_), (_e_), and (_f_), while at (_a_), (_b_), and (_c_) is shown its connection with the steam cylinder.

It will be observed that the valve itself is in the shape of a box with one side open, the edges of the open side being flanged. When the valve is in its middle position, as shown at (_a_), two of these flanged edges completely cover two rectangular openings S_{1} and S_{2}, called _steam ports_, while the hollow part of the valve is opposite to a third port E, called the _exhaust port_. As shown at (_a_) the piston P would be moving upwards and the valve downwards. By the time the piston has reached the top of its stroke the valve will have moved so far down as to partly uncover the steam port S_{1}, and admit steam from the valve casing C through S_{1} and the passage P_{1} to the top of the piston. The pressure of this steam on the top of the piston will force the latter down. While the above action has been going on, the port S_{2} will have become uncovered, and the hollow part of the valve will be opposite both the steam port S_{2} and the exhaust port E, so that the steam from the under side of the piston, and which forced the piston up, can now escape by the passage P_{2}, the steam port S_{2}, and the exhaust port E to the exhaust outlet O, and thence into the atmosphere, if it is a non-condensing engine, or into the condenser if it is a condensing engine, or into another cylinder if it is a compound engine. After the piston has performed, a certain part of its downward stroke, the valve, which has been moving downwards, will commence to move upwards, and when it has reached a certain point it will cover the port S_{1}, and shut off the supply of steam to the top of the piston. It is generally arranged that the steam shall be cut off before the piston reaches the end of the stroke. When the piston reaches the bottom of its stroke the valve has moved far enough up to uncover the port S_{2} and admit steam to the bottom of the piston, and to uncover the port S_{1} and allow the steam to escape from the top of the piston through the passage P_{1}, the port S_{1}, the port E, and outlet O. In this way the piston is moved up and down in the cylinder.

The valve is attached to a valve spindle S by nuts as shown, the hole in the valve through which the spindle passes being oval-shaped to permit of the valve adjusting itself so as to always press on its seat.

When the valve is in its middle position it generally more than covers the steam ports. The amount which the valve projects over the steam port on the outside, the valve being in its middle position, is called the _outside lap_ of the valve, and the amount which it projects on the inside is called the _inside lap_. When the term lap is used without any qualification, outside lap is to be understood. In fig. 58 it will be seen that the valve has no inside lap, and that the outside lap is three-eighths of an inch. The inside lap is generally small compared with the outside lap.

[Illustration: FIG. 58.]

When the piston is at the beginning of its stroke the steam port is generally open by a small amount called the _lead_ of the valve.

The reciprocating motion of the slide valve is nearly always derived from an eccentric fixed on the crank-shaft of the engine. Slide valves are generally made of brass, bronze, or cast iron.

EXERCISE 59: _Simple Slide Valve._--At (_d_), fig. 58, is shown a sectional elevation of a simple slide valve for a steam-engine, the section being taken through the centre line of the valve spindle, while at (_e_) is shown a cross section and elevation, and at (_f_) a plan of the same. Draw all these views full size, and also a sectional elevation at A B. The valve is made of brass, and the valve spindle and nuts of wrought iron.

EXERCISE 60: _Slide Valve Casing, &c., for Steam-engine._--Draw, half size, the views shown at (_a_), (_b_), and (_c_), fig. 58; also a sectional plan at L M. (_b_) is an elevation of the valve casing with the cover and the valve removed. (_a_) is a sectional elevation, the section being taken through the axes of the steam cylinder and valve spindle. (_c_) is a sectional plan, the section being a horizontal one through the centre of the exhaust port. The inlet and outlet for the steam are clearly shown in the sectional plan: in the sectional elevation their positions are shown by dotted circles.

The stroke of the piston is in this case 12 inches, so that from the dimensions given at (_a_) it must come within a quarter of an inch of each end of the cylinder; this is called the _cylinder clearance_.

The piston has three Ramsbottom rings, a quarter of an inch wide and a quarter of an inch apart.

The steam cylinder and valve casing are made of cast iron.

_Cocks._--A cock consists of a slightly conical plug which fits into a corresponding casing cast on a pipe. Through the plug is a hole which may be made by turning the plug to form a continuation of the hole in the pipe, and thus allow the fluid to pass, or it may be turned round so that the solid part of the plug lies across the hole in the pipe, and thus prevent the fluid from passing. As the student will be quite familiar with the common water cock or tap such as is used in dwelling-houses we need not illustrate it here.

[Illustration: FIG. 59.]

Fig. 59 shows a cock of considerable size, which may be used for water or steam under high pressure. The plug in this example is hollow, and is prevented from coming out by a cover which is secured to the casing by four stud bolts. An annular ridge of rectangular section projecting from the under side of the cover, and fitting into a corresponding recess on the top of the casing, serves to ensure that the cover and plug are concentric, and prevents leakage. Leakage at the neck of the plug is prevented by a gland and stuffing-box. The top end of the plug is made square to receive a handle for turning it. The size of a cock is taken from the bore of the pipe in which it is placed; thus fig. 59 shows a 2-1/4-inch cock.

EXERCISE 61: 2-1/4-_inch Steam or Water Cock._--First draw the views of this cock shown in fig. 59, then draw a half end elevation and half cross section through the centre of the plug. Scale 6 inches to a foot.

Instead of drawing the parts of the pipe on the two sides of the plug in the same straight line as in fig. 59, one may be shown proceeding from the bottom of the casing, so that the fluid will have to pass through the bottom of the plug and through one side. This is a common arrangement.

All the parts of the valve and casing in this example are made of brass.

XVII. MATERIALS USED IN MACHINE CONSTRUCTION.

_Cast Iron._--The essential constituents of cast iron are iron and carbon, the latter forming from 2 to 5 per cent. of the total weight. Cast iron, however, usually contains varying small amounts of silicon, sulphur, phosphorus, and manganese.

In cast iron the carbon may exist partly in the free state and partly in chemical combination with the iron.

In _white cast iron_ the whole of the carbon is in chemical combination with the iron, while in _grey cast iron_ the carbon is principally in the free state, that is, simply mixed mechanically with the iron. It is the free carbon which gives the grey iron its dark appearance. A mixture of the white and grey varieties of cast iron when melted produces _mottled cast iron_. The greater the amount of carbon chemically combined with the iron, the whiter, harder, and more brittle does it become.

The white cast iron is stronger than the grey, but being more brittle it is not so suitable for resisting suddenly applied loads. White iron melts at a lower temperature than grey iron, but after melting it does not flow so well, or is not so liquid as the grey iron. White iron contracts while grey iron expands on solidifying. The grey iron, therefore, makes finer castings than the white. Castings after solidifying contract in cooling about 1/8 of an inch per foot. Castings possessing various degrees of strength and hardness are produced by melting mixtures of various proportions of white and grey cast irons. White cast iron has a higher specific gravity than grey cast iron.

Cast iron gives little or no warning before breaking. The thickness of the metal throughout a casting in cast iron should be as uniform as possible, so that it may cool and therefore contract uniformly throughout; otherwise some parts may be in a state of initial strain after the casting has cooled, and will therefore be easier to fracture. Re-entrant angles should be avoided; such should be rounded out with fillets.

The presence of phosphorus in cast iron makes it more fusible, and also more brittle. The presence of sulphur diminishes the strength considerably.

The grey varieties of cast iron are called _foundry irons_ or _foundry pigs_, while the white varieties are called _forge irons_ or _forge pigs_, from the fact that they are used for conversion into wrought iron.

Amongst iron manufacturers the different varieties of cast iron are designated by the numbers 1, 2, 3, &c., the lowest number being applied to the greyest variety.

_Chilled Castings._--When grey cast iron is melted a portion of the free carbon combines chemically with the iron; this, however, separates out again if the iron is allowed to cool slowly; but if it is suddenly cooled a greater amount of the carbon remains in chemical combination, and a whiter and harder iron is produced. Advantage is taken of this in making _chilled castings_. In this process the whole or a part of the mould is lined with cast iron, which, being a comparatively good conductor of heat, chills a portion of the melted metal next to it, changing it into a hard white iron to a depth varying from 1/8 to 1/2 an inch. To protect the cast-iron lining of the mould from the molten metal it is painted with loam.

_Malleable Cast Iron._--This is prepared by imbedding a casting in powdered red hematite (an oxide of iron), and keeping it at a bright red heat for a length of time varying from several hours to several days according to the size of the casting. By this process a portion of the carbon in the casting is removed, and the strength and toughness of the latter become more like the strength and toughness of wrought or malleable iron.

_Wrought or Malleable Iron._--This is nearly pure iron, and is made from cast iron by the puddling process, which consists chiefly of raising the cast iron to a high temperature in a reverberatory furnace in the presence of air, which unites with the carbon and passes off as gas. In other words the carbon is burned out. The iron is removed from the puddling furnace in soft spongy masses called _blooms_, which are subjected to a process of squeezing or hammering called _shingling_. These shingled blooms still contain enough heat to enable them to be rolled into rough _puddled bars_. These puddled bars are of very inferior quality, having less than half the strength of good wrought iron. The puddled bars are cut into pieces which are piled together, reheated, and again rolled into bars, which are called _merchant bars_. This process of piling, reheating, and re-rolling may be repeated several times, depending on the quality of iron required. Up to a certain point the quality of the iron is improved by reheating and rolling or hammering, but beyond that a repetition of the process diminishes the strength of the iron.

The process of piling and rolling gives wrought iron a fibrous structure. When subjected to vibrations for a long time, the structure becomes crystalline and the iron brittle. The crystalline structure induced in this way may be removed by the process of _annealing_, which consists in heating the iron in a furnace, and then allowing it to cool slowly.

_Forging and Welding._--The process of pressing or hammering wrought iron when at a red or white heat into any desired shape is called _forging_. If at a white heat two pieces of wrought iron be brought together, their surfaces being clean, they may be pressed or hammered together, so as to form one piece. This is called _welding_, and is a very valuable property of wrought iron.

_Steel._--This is a compound of iron with a small per-centage of carbon, and is made either by adding carbon to wrought iron, or by removing some of the carbon from cast iron.

In the _cementation_ process, bars of wrought iron are imbedded in powdered charcoal in a fireclay trough, and kept at a high temperature in a furnace for several days. The iron combines with a portion of the carbon to form _blister steel_, so named because of the blisters which are found on the surface of the bars when they are removed from the furnace.

The bars of blister steel are broken into pieces about 18 inches long, and tied together in bundles by strong steel wire. These bundles are raised to a welding heat in a furnace, and then hammered or rolled into bars of _shear steel_.

To form _cast steel_ the bars of blister steel are broken into pieces and melted into crucibles.

In the _Siemens-Martin_ process for making steel, cast and wrought iron are melted together on the hearth of a regenerative gas-furnace.

_Bessemer steel_ is made by pouring melted cast iron into a vessel called a converter, through which a blast of air is then urged. By this means the carbon is burned out, and comparatively pure iron remains. To this is added a certain quantity of 'spiegeleisen,' which is a compound of iron, carbon, and manganese.

_Hardening and Tempering of Steel._--Steel, if heated to redness and cooled suddenly, as by immersion in water, is hardened. The degree of hardness produced varies with the rate of cooling; the more rapidly the heated steel is cooled, the harder does it become. Hardened steel is softened by the process of _annealing_, which consists in heating the hardened steel to redness, and then allowing it to cool slowly. Hardened steel is _tempered_, or has its degree of hardness lowered, by being heated to a temperature considerably below that of a red heat, and then cooling suddenly. The higher the temperature the hardened steel is raised to, the lower does its 'temper' become.

_Case-hardening._--This is the name given to the process by which the surfaces of articles made of wrought iron are converted into steel, and consists in heating the articles in contact with substances rich in carbon, such as bone-dust, horn shavings, or yellow prussiate of potash. This process is generally applied to the articles after they are completely finished by the machine tools or by hand. The coating of steel produced on the article by this process is hardened by cooling the article suddenly in water.

_Copper._--This metal has a reddish brown colour, and when pure is very malleable and ductile, either when cold or hot, so that it may be rolled or hammered into thin plates, or drawn into wire. Slight traces of impurities cause brittleness, although from 2 to 4 per cent. of phosphorus increases its tenacity and fluidity. Copper is a good conductor of heat and of electricity. Copper is largely used for making alloys.

_Alloys._--_Brass_ contains two parts by weight of copper to one of zinc. _Muntz metal_ consists of three parts of copper to two of zinc. Alloys consisting of copper and tin are called _bronze_ or _gun-metal_. Bronze is harder the greater the proportion of tin which it contains; five parts of copper to one of tin produce a very hard bronze, and ten of copper to one of tin is the composition of a soft bronze. _Phosphor bronze_ contains copper and tin with a little phosphorus; it has this advantage over ordinary bronze, that it may be remelted without deteriorating in quality. This alloy also has the advantage that it may be made to possess great strength accompanied with hardness, or less strength with a high degree of toughness.

_Wood._--In the early days of machines wood was largely used in their construction, but it is now used to a very limited extent in that direction. _Beech_ and _hornbeam_ are used for the cogs of mortise wheels. _Yellow pine_ is much used by pattern-makers. _Box_, a heavy, hard, yellow-coloured wood, is used for the sheaves of pulley blocks, and sometimes for bearings in machines. _Lignum-vitæ_ is a very hard dark-coloured wood, and remarkable for its high specific gravity, being 1-1/3 times the weight of the same volume of water. This wood is much used for bearings of machines which are under water.

XVIII. MISCELLANEOUS EXERCISES.

The illustrations in this chapter are in most cases not drawn to scale; they are also in some parts incomplete, and in others some of the lines are purposely drawn wrong. The student must keep to the dimensions marked on the drawings, and where no sizes are given he must use his own judgment in proportioning the parts. All errors must be corrected, and any details required, but not shown completely in the illustrations, must be filled in.

EXERCISE 62: _Single Riveted Butt Joint with Tee-iron Cover Strap._--Two views, one a side elevation and the other a sectional elevation, of a riveted joint are shown in fig. 60. Draw these views, and also a plan projected from one of them. Show the rivets completely in all the views. Scale 4 inches to a foot.

[Illustration: FIG. 60.]

[Illustration: FIG. 61.]

EXERCISE 63: _Girder Stay for Steam Boiler._--The flat crown of the fire-box of locomotive and marine boilers is generally supported or stayed by means of girder stays, an example of which is shown in fig. 61. A B is the side elevation of a portion of one of these girders. Each girder is supported at its ends by the plates forming the vertical sides of the fire-box. The flat crown is bolted to the girders as shown. Observe that the girders are in contact with the crown only in the neighbourhood of the bolts. Consider carefully this part of the design, and then answer the following questions: (1) What objections are there to supporting the girders at the ends only without the contact pieces at the bolts? (2) What objections are there to having the girders in contact with the crown plate of the fire-box throughout their whole length?

Draw the views shown in fig. 61, and from the right-hand one project a plan. Scale 4 inches to a foot.

[Illustration: FIG. 62.]

EXERCISE 64: _End of Bar Stay for Steam Boiler._--On page 12 one form of stay for supporting the flat end of a steam boiler is described. Another form of stay for the same purpose is shown in fig. 62. A B is a portion of the end of a steam boiler. C D is one end of a bar which extends from one end of the boiler to the other. The ends of this bar are screwed, and when the bar is of wrought iron the screwed parts are generally larger in diameter than the rest of the bar. When made of steel the bar is generally of uniform diameter throughout. In the case of wrought-iron bar stays the enlarged ends are welded on to the smaller parts. Welding is not so reliable with steel as with wrought iron. Write out answers to the following questions: (1) What is the advantage of having the screwed part of the bar larger in diameter than the rest? (2) Why are steel bar stays not generally enlarged at their screwed ends?

Draw the views shown in fig. 62, and project from one of them a third view. Scale 4 inches to a foot.

EXERCISE 65: _Knuckle Joint._--Draw the plan and elevation of this joint shown in fig. 63, and also draw an end elevation looking in the direction of the arrow. The parts at A and B are octagonal in cross section. Scale 4 inches to a foot.

[Illustration: FIG. 63.]

EXERCISE 66: _Locomotive Coupling Rod Ends._--A form of knuckle joint used on locomotive coupling rods is shown in fig. 64.

In this case two rods meet and work on the same pin, as shown at (a) fig. 64. Draw, in addition to the views shown in fig. 64, a plan and a vertical section through the axis of the pin. Scale 6 inches to a foot.

Would it be practicable to replace the two rods A B and B C by a single rod working on the crank pins at A, B, and C? Give reasons for your answer.

[Illustration: FIG. 64.]

EXERCISE 67: _Bell Crank Lever._--Draw the plan and elevation of the lever shown in fig. 65. Scale 6 inches to a foot.

[Illustration: FIG. 65.]

EXERCISE 68: _Back Stay for Lathe._--Draw a plan and two elevations of the stay shown in fig. 66. Make all necessary corrections and show all the details in each view. Scale full size.

[Illustration: FIG. 66.]

[Illustration: FIG. 67.]

EXERCISE 69: _Conical Disc Valve and Casing._--Draw, half size, the views shown in fig. 67 of the conical disc valve and casing, and also add an elevation looking in the direction of the arrow.

EXERCISE 70: _Connecting Rod End._--The student should carefully compare this connecting rod end (fig. 68) with those illustrated on pages 50 and 52. The lower part of fig. 68 is a half plan and half horizontal section, and the upper part is a half side elevation and half vertical section. Draw these views and also an end elevation. Scale 6 inches to a foot.

[Illustration: FIG. 68.]

[Illustration: FIG. 69.]

[Illustration: FIG. 70.]

[Illustration: FIG. 71.]

[Illustration: FIG. 72.]

[Illustration: FIG. 73.]

[Illustration: FIG. 74.]

EXERCISE 71: _Engine Cross-head._--The cross-head shown in fig. 69 is for an inverted cylinder marine engine. A is the piston rod, and B B are pins, forged in one piece with C, to which the forked end of the connecting rod is attached. Draw the upper view with the central part in section as shown. Make the right-hand half of the lower view a plan without any section, and make the left-hand half a horizontal section through the axis of the pins B B. Scale 4 inches to a foot.

EXERCISE 72: _Ratchet Lever._--The lever shown in fig. 70 is used for turning the horizontal screw of a traversing screw jack. Draw the two views shown, and from one of them project a plan. Scale full size.

EXERCISE 73: _Steam Whistle._--Draw, full size, the elevation and section of the steam whistle shown in fig. 71. Draw also horizontal sections at A B, C D, and E F.

[Illustration: FIG. 75.]

EXERCISE 74: _Screw Coupling for Railway Carriages._--Draw the three views of the screw coupling shown in fig. 72. Scale 6 inches to a foot.

If the link A is fixed, through what distance will the link B move for two turns of the lever?

[Illustration: FIG. 76.]

EXERCISE 75: _Loose Headstock for a 6-inch Lathe._--Two views of this headstock are shown in fig. 73. On one of these views a few of the chief dimensions are marked. The details, fully dimensioned, are shown separately in figs. 74, 75, and 76.

Explain clearly how the centre is moved backwards and forwards, and also how the spindle containing it is locked when it is not required to move.

Draw, half-size, the views shown in fig. 73, and from the left-hand view project a plan. Draw also the detail of the locking arrangement shown in fig. 74.

APPENDIX A.

_SCIENCE AND ART DEPARTMENT, SOUTH KENSINGTON._

SYLLABUS.

SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.

It is assumed that the student has already learnt to draw to scale, and that he can draw two or more views of the same object in simple or orthographic projection. To pass in machine construction and drawing, he must be able to apply this knowledge to the representation of machinery. He must be acquainted with the form and purpose of the simpler parts of which machines are built up and must have had some practice in drawing them. To test his knowledge, rough dimensioned sketches, more or less incomplete, of simple machine details will be given him, and he will be required to produce a complete drawing in pencil to a given scale. Two or more views of at least one subject will be required, and these must be so drawn as to be properly projected one from the other, _in order to show that the student appreciates that he is producing a representation of a solid piece of machinery, and not merely copying a sketch. No credit will be given unless some knowledge of projection is shown._ The centre lines of the drawings should be shown, and parts cut by planes of section should be indicated by diagonal shading. Bolts and other fastenings should be carefully shown where required. Any indication that a candidate has merely copied the sketches given, without understanding the part represented, will invalidate his examination.

FIRST STAGE OR ELEMENTARY COURSE.

In the elementary stage, a knowledge is required of the simple parts only of _machines in common use_. _Some_ of these are enumerated in the following list. The student should be practised in drawing them till he recognises their forms, and the object of the arrangement should be explained to him. He should also know the simple technical terms used in describing them.

A few very simple questions relating to the arrangement, proportions, and strength of the simplest machine details will be set in the examination paper.

In drawing the examples set to test a student's knowledge and skill in machine drawing, it must be remembered that only a limited time is available. It is only possible to set an example to be drawn in pencil, and the points which will receive attention are (1) accuracy of scale and projection; (2) power of reading a drawing, shown by the ability to transfer portions of the mechanism and dimensions from one view to another; (3) knowledge of machines, as shown by the ability to fill in small details, such as nuts, keys, etc., omitted in the sketches given. Bearing in mind the limited time available, the student should try to make his outline clear and decisive and complete. But the diagonal lines necessary for sectional parts may be done rapidly, though neatly, by freehand if necessary.

_Riveted Joints._--Forms of rivets and arrangement of rivets in lap and butt joints with single and double riveting. Junction of plates by angle and T-irons.

_Bolts, Studs, and Set Screws._--Forms of these fastenings. Forms and proportions of nuts and bolt-heads. Arrangement of flanges for bolting.

_Pins, Keys, and Cotters._--Form of ordinary knuckle joint. Use of split pins. Connection of parts by a key. Connection of parts by a cotter. Gib and cotter.

_Pipes and Cylinders._--Forms of ordinary pipes and cylinders and their flanges and covers.

_Shafting._--Forms of shafts and axles and of journals and pivots. Use of collars and bosses. Half-lap coupling. Box coupling. Flange coupling.

_Pedestals and Plummer Blocks._--Simplest forms of pedestals and hangers for shafts. Form and arrangement of brass steps. Arrangements for fixing pedestals and for neutralising the effects of wear.

_Toothed Gearing._--Forms of ordinary spur and bevil wheels. Meaning of the terms pitch, breadth of face, thickness of tooth, pitch line, rim, nave, arm. Mode of drawing bevil wheels in section.

_Belt Pulleys._--Forms of belt pulleys for flat and round belts. Stepped speed cones. Drawing of pulleys with curved arms.

_Cranks and Levers._--Forms of ordinary cast-iron and wrought-iron cranks and levers. Modes of fixing crank pin. Modes of fixing crank shaft. Double cranks. Form of eccentrics.

_Links._--Most simple forms of connecting rod ends, open or closed. Use of steps in connecting rods. Use of cotters to tighten the steps.

_Pistons._--Simple forms of piston. Use of piston packing. Modes of attaching piston rod.

_Stuffing-Boxes._--Simple form of stuffing-box and gland. Use of packing. Mode of tightening gland.

_Valves._--Simple conical of puppet valve. Simple slide valve. Cock or conical sliding valve.

APPENDIX B.

_EXAMINATION PAPERS SET BY THE SCIENCE AND ART DEPARTMENT._

SUBJECT II.--MACHINE CONSTRUCTION AND DRAWING.

_Examiners_, PROF. T. A. HEARSON, M.Inst.C.E., and J. HARRISON, ESQ., M.Inst.M.E.

GENERAL INSTRUCTIONS.

_If the rules are not attended to, the paper will be cancelled._

You may take the Elementary, or the Advanced, or the Honours paper, but you must confine yourself to one of them.

Put the number of the question before your answer.

You are expected to prove your knowledge of machinery as well as your power of drawing neatly to scale. You are therefore to supply details omitted in the sketches, to fill in parts left incomplete, and to indicate, by diagonal lines, parts cut by planes of section.

No credit will be given unless some knowledge of projection is shown, so that at least two views of one of the examples will be required properly projected one from the other. The centre lines should be clearly drawn. The figured dimensions need not be inserted.

Your answers should be clearly and cleanly drawn in pencil. No extra marks will be allowed for inking in.

All figures must be drawn on the single sheet of paper supplied, for no second sheet will be allowed.

The value attached to each question is shown in brackets after the question. But a full and correct answer to an easy question will in all cases secure a larger number of marks than an incomplete or inexact answer to a more difficult one.

Your name is not given to the Examiner, and you are forbidden to write to him about your answers.

You are to confine your answers _strictly_ to the questions proposed.

A single accent (') signifies _feet_; a double accent (") _inches_.

_The examination in this subject lasts for four hours._

* * * * *

First Stage or Elementary Examination. 1885.

INSTRUCTIONS.

Read the General Instructions above.

Answer briefly any three, but not more than three, of the following questions, and draw two, but not more than two, of the examples.

_Questions._

(_a._) Show two methods by which a cotter may be prevented from slacking back. (6.)

(_b._) Sketch the brasses for a bearing, and show how they are prevented from turning in the pedestal. (6.)

(_c._) Explain the object of the construction of the connecting rod end shown in fig. 78. Describe how the adjustment must be made and how it is locked. (10.)

(_d._) Show the form of the Whitworth screw thread by drawing to scale a part section of two or three threads taking a pitch of 1-1/2 inches. Figure the dimensions on the sketch. How many threads to the inch are used on an inch bolt? (10.)

(_e._) Make a sketch showing how the adjustment is made in the sliding parts of machine tools: as, for example, in the slide rest of a lathe. (10.)

(_f._) Describe with sketches two methods by which the joints are made in connecting lengths of cast-iron pipes. (6.)

_Examples to be drawn._

1. Jaw for four-screw dog chuck for 5" lathe. Draw the two views as shown (fig. 77). Scale full size.

(Note.--The other three jaws of the chuck are not to be drawn.) (35.)

2. Connecting rod end. Draw the two views as shown, partly in section (fig. 78). Draw full size. (35.)

3. Hooke's coupling. Draw the three views shown (fig. 79), adding any omitted lines where the views are incomplete. Draw to scale of 1/4 full size. (35.)

[Illustration: FIGS. 77 AND 78.]

[Illustration: FIG. 79.]

* * * * *

First Stage or Elementary Examination. 1886.

INSTRUCTIONS.

Read the General Instructions (page 102).

Answer briefly any three, but not more than three, of the following questions, and draw two, but not more than two, of the examples.

_Questions._

(_a._) Give sketches showing how the cutting tool of a lathe or other machine is secured in place. (6.)

(_b._) Make a sketch of a stud, describe how it is screwed into place, and state some circumstances under which it is used in preference to a bolt. (6.)

(_c._) Give sketches showing one method of attaching the valve rod to an ordinary slide valve. (6.)

(_d._) Sketch a connecting rod end, with strap, gib, and cotter. Explain the use of the gib. (10.)

(_e._) Explain the use of the quadrant for change wheels for a screw-cutting lathe shown in Example 1, fig. 80, by making a sketch showing it in place on a lathe with wheels in gear. (10.)

(_f._) Sketch one form of hanger suitable for supporting mill-shafting. (10.)

_Examples to be drawn._

1. Quadrant for change wheels for screw-cutting lathe. Draw the two views shown (fig. 80). Scale half-size. (35.)

2. Crank-shaft. Draw the two views as shown, partly in section (fig 81). Scale 1/8 full size. (35.)

3. Ball bearing for tricycle. Draw the two views as shown, partly in section (fig. 82). Draw full size. (35.)

[Illustration: FIGS. 80 AND 81.]

[Illustration: FIG. 82.]

* * * * *

First Stage or Elementary Examination. 1887.

INSTRUCTIONS.

Read the General Instructions (page 102).

Answer briefly any three, but not more than three, of the following questions, and draw two, but not more than two, of the examples.

_Questions._

(_a._) Explain how the piston rings in Example 1, fig. 84, are made so that the piston may work steam-tight in the cylinder. How are these rings got into place? (8.)

(_b._) Give two views of a double riveted lap joint for boiler-plates. (8.)

(_c._) Show by sketches how a wheel is fixed on a shaft by means of a sunk key. Explain how the key may be withdrawn when it cannot be driven from the point end. (8.)

(_d._) Give sketches showing the construction of a conical metal lift or puppet valve and seating. (10.)

(_e._) With the aid of sketches explain how a piston rod is made to work steam-tight through the end of the cylinder. (10.)

(_f._) Explain how the slotting machine ram of Example 8, fig. 85, may be made to move up and down when at work. How is the length of the stroke altered, and what is the object of the slotway in the upper part of the ram? (10.)

_Examples to be drawn._

1. Piston for steam-engine. Draw and complete the two views shown (fig. 84), the top half of the left-hand view to be in section. Scale 1/2 size. (30.)

2. Plan and sectional elevation of a footstep bearing for an upright shaft (fig. 83). Draw and complete these views. Scale 1/4 size. (35.)

3. Ram of slotting machine. Draw and complete the two elevations shown (fig. 85). The tool-holders must be drawn in their proper positions in the ram, and not separate as in the diagram. Scale 1/4 size. (35.)

[Illustration: FIGS. 83 AND 84.]

[Illustration: FIG. 85.]

* * * * *

First Stage or Elementary Examination. 1888.

INSTRUCTIONS.

Read the General Instructions on p. 102.

Answer briefly any three, but not more than three, of the following questions, and draw two, but not more than two, of the examples.

_Questions._

(_a._) Give sketches showing how the separate lengths of a line of shafting may be connected together. (8.)

(_b._) What is the object of using chipping or facing strips in fitting up machine parts? Give one or two examples. (8.)

(_c._) Give sketches showing how you would grip and drive a round iron bar for the purpose of turning it between the centres of a lathe. (10.)

(_d._) Explain the action of the governor shown in Example 1 (fig. 86). (10.)

(_e._) Describe in detail how the mud-hole door in Example 2 (fig. 88) is removed for the purpose of cleaning the boiler and how it is replaced and the joint made steam-tight. (10.)

(_f._) Describe how the parts of the spur wheel in Example 3 (fig. 87) are put together, and explain why the wheel is made in segments. (10.)

_Examples to be drawn._

1. Loaded governor for small gas engine. Draw and complete the two views, partly in section as shown (fig. 86). Scale full size. (35.)

2. Mud-hole mouth-piece for Lancashire boiler. Draw and complete the two views shown (fig. 88). Scale 3/8ths. (35.)

3. Point for segments of large spur wheel. Draw and complete the views shown (fig. 87). Scale 3/16ths.

_Note._--As the radius of the wheel is too large for your instruments, the circumference at the joint may be set out straight, as in a rack. (35.)

[Illustration: FIGS. 86 AND 87.]

[Illustration: FIG. 88.]

INDEX

Air-pump bucket, 58 Alloys, 80 Angle irons, 12 Annealing, 79, 80 Axles, 24

Back stay for lathe, 86 Bar stay, 83 Bearings for shafts, 30 Beech-wood, 81 Bell crank lever, 86 Bessemer steel, 79 Bevil wheels, 43 Blister steel, 79 Blooms, 78 Bolt-heads, proportions of, 18 Bolts, forms of, 17 Border lines, 4 Box couplings, 25 -- end, connecting rod, 51 Box-wood, 81 Brackets, 33 Brake shaft carrier, 30 Brass, 80 Brasses, 30 Bucket, 58 Built-up cranks, 46 Bush, 30, 49, 51, 54, 56, 63 Butt joints, 10, 11 -- strap, 10 Buttress screw thread, 15

Case-hardening, 80 Cast iron, 76 Cast iron flange coupling, 28, 29 -- steel, 79 Caulking, 8 Cementation process, 79 Centre lines, 2, 4 Chilled castings, 78 Circulating pump piston, 58 Clearance, cylinder, 74 -- of cotter, 49 Cocks, 74 Cogs, 41 -- wood for, 81 Collared stud, 18 Collars, 24 Colouring, 3 Colours for different materials, 3 Compasses, 1 Cone keys, 23, 38 Conical disc valve, 70, 71, 89 -- head, 7 Connecting rod, locomotive, 51 -- -- marine, 51 -- rods, 49, 89 Construction for rivet heads, 7 Contraction of castings, 77 Copper, 80 Cotters, 48, 49 Countersunk head, 7, 18 Coupling rod ends, 55, 84 -- rods, 54 -- screw, 96 Couplings, shaft, 25 Cover plate, 10 Cranked axle, 45 Cranks, 43 -- built-up, 46 Cross-head pin, 51 Cross-heads, 56, 89 Cross-key, 28 Cup-headed bolt, 17

Decimal equivalents, 6 Dimension lines, 5 Dimensions, 5 -- of box couplings, 26 -- cast-iron flange couplings, 29 -- keys, 24 -- stuffing-boxes and glands, 67 -- Whitworth screws, 15 Distance lines, 5 Dividers, 1 Draught of cotter, 49 Drawing board, 1 -- instruments, 1 -- paper, 2 -- pen, 1 -- pins, 2

Eccentrics, 47 Exhaust port, 71 Eye-bolt, 18

Fairbairn's coupling, 26 Fast and loose pulleys, 37 Feather key, 23 Flange couplings, 27 Flap valves, 68 Flat key, 22 Forge irons, 77 Forging, 79 Form of wheel teeth, 40 Forms of nuts, 16 -- rivet heads, 7 -- screw threads, 15 Foundry irons, 77

Gasket, 58 Gas threads, 15 Gib, 49 -- head, 23 Girder stay, 81 Gland, 64 Grey cast iron, 77 Gun-metal, 80 Gusset stay, 12

Half-lap coupling, 26 Hangers, 34 Hardening of steel, 80 Headstock lathe, 96 Hexagonal nut, 16 Hollow key, 22 Hook bolt, 18 Hornbeam, 81

India-rubber disc valves, 58, 68 Inking drawings, 2 Inside lap of valve, 72

Joggles, 33 Joint, knuckle, 84 Journals, 24 -- length of, 32 Junk ring, 61

Keys, 22 -- proportions of, 23 Kinghorn's metallic valve, 70 Knuckle joint, 84 -- screw thread, 15

Lancaster's piston packing, 61 Lap joints, 8, 9, 10, 12 -- of slide valve, 72 Lathe headstock, 96 Lead of valve, 74 Lever, bell crank, 86 -- ratchet, 96 Lignum-vitæ, 81 Locking arrangements for nuts, 21, 62 Lock nuts, 19 Locomotive connecting rod, 51 -- cranked axle, 45 -- cross-head, 56 Locomotive eccentric, 47 -- piston, 60 Lubricator, needle, 32

Malleable cast iron, 78 -- iron, 78 Marine connecting rod, 51 -- coupling, 28 -- crank-shaft, 46 -- piston, 61 Merchant bars, 78 Mortise wheels, 41 Mottled cast iron, 77 Muff couplings, 25 Muntz metal, 80

Needle lubricator, 32 Nuts, forms of, 16 -- lock, 19 -- proportions of, 18

Oil-box, 54, 65 Outside lap of slide valve, 72 Overhung crank, 43 -- cranks, proportions of, 45

Packing, 63 Pan head, 7 Pedestal, shaft, 30 Pencils, drawing, 1 Phosphor bronze, 80 Pillar bracket, 34 Pillow block, 30, 32 Pin, cross-head, 51, 54 -- split, 21 Piston rod, 57 Pistons, 57 Pitch circle, 40 -- of wheel teeth, 40 -- surfaces of wheels, 39, 43 Pivots, 24 Plummer block, 30 Plunger, 57 Printing, 4 Proportions of bolt-heads, 18 -- keys, 23 Proportions of lap joints, 9, 10 -- marine engine pistons, 62 -- nuts, 18 -- overhung cranks, 45 -- pillow blocks, 32 -- rivet heads, 7 -- wheel teeth, 40 Puddled bars, 78 Puddling process, 78 Pulley, eccentric, 47 Pulleys, 36 Pump bucket, 58

Ramsbottom's packing, 60 Ratchet lever, 96 Riveted joints, 8 Rivet heads, forms of, 7, 8 -- -- proportions of, 7 Riveting, 7 Rivets, 6 Rope pulley, 39 Round key, 23

Saddle key, 22 Scales, 5 Screw coupling, 96 Screwed gland and stuffing-box, 65 Screw threads, 14, 15 Screws, representation of, 16 Sellers =V= screw thread, 14 Set screw, 21, 49 -- squares, 1 Shaft couplings, 25 -- hanger, 34 Shafting, 24 Shear steel, 79 Sheave, eccentric, 47 Shingling, 78 Shrinking, process of, 44 Siemens-Martin steel, 79 Slide blocks, 56 -- valves, 68, 71 Sliding key, 23 Snap head, 7 Snug, 17 Spiegeleisen, 80 Spring bows, 1 Spur wheel, 41 Square nut, 16 -- screw thread, 14 Stay, back, for lathe, 86 -- bar, 83 -- girder, 81 -- gusset, 12 Steam ports, 71 -- whistle, 96 Steel, 79 Steps, 30 Strap, 49 -- eccentric, 47 -- end of connecting rod, 49 Stud bolts, 18 Studs, 18 Stuffing-boxes, 63 Sunk key, 22

Taper bolt, 18, 27 -- pin, 23 Tee-headed bolt, 18 Tee-iron cover strap, 81 Tee square, 1 Teeth of wheels, form and proportions of, 40 Teeth, pitch of, 40 Tempering of steel, 80 Throw of crank, 44 -- eccentric, 47 Toothed wheels, 39

Valve Kinghorn's metallic, 70 -- slide, 68, 71 Valves, 68 -- conical disc, 70 -- india-rubber, 58, 68 Velocity ratio in belt gearing, 36

Wall boxes, 34 Washers, 19 Welding, 79 Whistle, steam, 96 White cast iron, 77 Whitworth screws, dimensions of, 15 -- =V= screw thread, 14 Wood, 81 Working drawings, 4 Wrought iron, 78

Yellow pine, 81

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