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.