CHAPTER IV

USE OF JIGS AND FIXTURES

#43. Value of Jigs and Fixtures.#--The use of jigs, fixtures, and other labor-saving devices is an important factor in illustrating industrial and practical applications in the school shop. It is advisable to let each group of boys work out its own jig or fixture for the particular job they have on hand.

The three most common forms of jigs are cutting jigs, boring jigs, and assembling jigs. The important reasons for the use of such devices are: (1) They illustrate the speed of output in shop work. (2) They give the student a good idea of machine operation. (3) They help in making the parts interchangeable. (4) They offer an opportunity for getting first hand information on cutting edge tools and their proper uses. (5) They show the boy the value of the use of jigs in factory work.

The toys illustrated in this book have many simple operations, such as cutting stock to length, drilling holes, surfacing, etc., that can be easily done by the use of the proper fixtures.

For that reason toys are desirable projects to be made by the productive plan. Fig. 18 shows the use of a jig and the miter box.

#44. Cutting Small Wheels.#--A circle of the desired size wheel may be laid out on the wood with the aid of a compass, and cut in the outline with a coping saw or band saw. Of course, it would take quite a long time by this method to make the small wheels in large quantities and besides the result would not be as good as when the wheels are made by machine.

#45. Turning Wheels.#--Another way to produce wheels is to turn a cylinder to the required diameter, on the turning lathe. Then cut the cylinder on the circular saw into required thicknesses of wheels desired. This method is recommended for quick work.

[Illustration: Fig. 18. Production of toys by use of jigs]

If it is desired to round the end of wheels the operation can be done by leaving the cylinder in the lathe and applying the broad side of the skew chisel as shown in Fig. 33. The wheels may then be polished with a cloth after they have been sanded and while rotating in the lathe as shown in Fig. 34. In sanding, use first a fairly course grade of sandpaper, No. 1 or 1-1/2 and afterwards a fine grade, No. O or OO. Before applying the cloth the wood may be varnished lightly while the lathe is not running, taking care to wipe off all the surplus varnish. The varnish will assist in giving the surface a fine polish when the cloth is applied. For further explanations of the use of the turning lathe, see Sec. 55.

#46. Use of Wheel Cutter.#--Still another method of making small wheels is by use of the wheel cutter as shown in Fig. 19. This wheel cutter may be used in the ordinary bit brace. Good results may be obtained where the wheels are made out of thin, soft wood.

This wheel cutter is known on the market as a leather washer cutter. If one cannot be obtained it can easily be made in the school machine shop at a small cost. Fig. 20 shows a drawing of a wheel cutter.

You will notice that the blade can be adjusted to cut any diameter desired.

#47. Use of Coping Saw.#--Where a band saw is not included in the shop equipment, many articles such as animal forms and small wheels could very easily be cut out with a coping saw.

[Illustration: Fig. 19. Wheel cutter in use]

A saw board, as shown in Fig. 21 should be fastened to a table top with an iron clamp; or, a saw board made to fasten in a vise may also be used.

[Illustration: Fig. 20. Details of a wheel cutter which may be made in school]

When cutting out the toy part, the coping saw should be held in a vertical position as shown in Fig. 22, and in an up-and-down motion, with short fast strokes, following the outline carefully. Cut on the line. Do not press hard on the saw for the blade is very thin and can very easily be broken, but it should last a long time if used correctly.

[Illustration: Fig. 21. Clamping the saw board to the bench]

[Illustration: Fig. 22. Correct method of holding coping saw]

#48. Cutting Sharp Corners.#--When cutting a sharp turn in the wood with the coping saw, care should be taken not to twist the saw blade out of shape. Upon reaching the sharp turn, continue the up-and-down motion, but without doing any cutting; turn the wood very slowly until you have made the complete turn, then continue with the sawing and follow the rest of the outline carefully.

[Illustration: Fig. 23. Removing the saw-blade]

#49. Removing the Saw-Blade from Frame.#--To remove the saw-blade from the frame, place the head of the frame against the table top as shown in Fig. 23. Pressing down on the handle will release the saw-blade. When inserting the blade into the frame the same method may be followed, being careful that the teeth of the saw-blade point toward the handle of the frame. The blade may be put in the end or the side slots of the frame, using the side slots only when the end slots will not serve the purpose.

#50. Making Heavy Wheels.#--In turning heavier wheels that are to be used for coasters, kiddie cars, etc., the work is done with the head stock only, the wood being supported by the screw-center chuck or face plate.

In turning the wheel the first step is the scraping cut as shown in Fig. 24. This cut is properly made with the concave chisel held in such a position as to give a light scraping cut. Care should be exercised not to allow the chisel to extend too deeply, otherwise the material will chip with the grain.

After the desired circumference has been obtained the surface should be worked to the desired form as shown in Fig. 25. This is accomplished by using the lathe rest, set at right angles with the bed or parallel with the face plate. The illustration in Fig. 26 shows the use of the dividers in marking off the position of the various corrugations in the wheel that is being turned. The sanding should be done while the wheel is in the lathe. Use first a fairly course grade of sand paper and afterwards a fine grade, No. O or OO.

#51. Designs for Wheels.#--Suggestions for wooden toy wheels are shown in Fig. 27. Those numbered 1, 2, 3, 4, 5, 6, and 7 are plain wooden wheels varying in design only. No. 8 and 9 are re-enforced with zinc and large iron washers. No. 10 shows a segment of an iron pipe fitted in the center of the wheel to prevent wearing away of material. No. 11 shows a spoke wheel. The spokes are made of dowel rods; these fitting into a hub that can easily be turned out on the lathe. No. 13 shows a wheel built in segments which is then cut out on the band saw to resemble a standard spoke wheel. The rim is 1/8" steel, fastened to spokes with very small rivets.

[Illustration: Fig. 24. Making heavy wheels. The scraping cut]

#52. Cutting Wheels on Band-Saw.#--A circle of the required size wheel may be marked off on the wood with a compass, then cut in the outline on the band-saw. This method will leave square corners and will be more or less out of truth with the center of the wheel. To true up and smooth the outside of the wheel the lathe attachment as shown in Fig. 28 can be easily prepared. This attachment consists of a block _A_ fastened to the lathe bed with a single bolt, and a stop _B_ fastened to the upper face of the block _A_. The carriage _C_ is a loose piece the same thickness as the stop _B_ and is provided with a dowel rod to fit the central hole in the wheel. This dowel rod is so located that when the edge of the carriage _C_ is tight against the edge of the stop _D_, the distance from the center of the dowel rod to the face of the abrasive material on the disk, will be equal to the radius of the finished wheel.

[Illustration: Fig. 25. Smoothing the side of wheels]

The wood is cut out on the band saw a scant 1/16" over-size in diameter, and is then placed on the dowel rod in the carriage _C_ which is held flat on block _A_ while the edge of the blank is brought in contact with the grinding disc face by pushing the carriage forward with the left hand while the blank is slowly revolved with the right. This grinding is continued until the edges of stop _B_ and carriage _C_ will remain in contact during a complete revolution of the wheel blank. During this grinding process, the carriage should be moved back and forth from the edge to the center of the grinding disc so that the wear on the abrasive material may be equalized.

[Illustration: Fig. 26. Using dividers to mark for cuts]

A similar device used for chamfering the edges of the blanks is also shown in Fig. 28, as it looks when viewed from the front of the lathe. The preceding description will suffice for this as the same system of lettering has been used. It differs only in that block _A_ is made to set at an angle of 45 degrees instead of being level.

[Illustration: Fig. 27. Many ways of making wheels for toys]

[Illustration: Fig. 28. Simple attachments which may be made for lathe]

Grinding discs may be made either of metal or wood. Metal is preferable but a hardwood disc fastened to a metal face plate will answer very well. There are many methods of fastening the abrasing material to the disc but the most convenient way is by the use of stick belt dressing. The disc is coated with dressing by holding the stick against it as it revolves and the abrasive is applied before the dressing has set. A pair of dividers or trammels is used to cut the abrasive material to the same diameter as the disc and it should be warmed on the uncoated side before it is applied. It sticks tightly to the disc but is easily removed and replaced with fresh material in a few minutes.

#53. Boring Holes in Wheels.#--The center holes in wheels may be bored with bit and brace, but better results are obtained if the holes are bored in the lathe. A drill chuck fitted to the live spindle and a drilling pad for the tail stock spindle will be required to do this job efficiently. The tail stock is locked fast and the wheel to be drilled is placed against the drilling pad and fed up to the revolving bit by turning the tail spindle feed wheel. This method will produce a cleaner hole and one that is square with the wheel face.

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