gearwheel, say 1 in. outside
diameter and 1/16 in. thick, with twenty-four teeth. Draw a circle
on paper, the same diameter as the wheel. Divide the circumference
into the number of parts desired, by drawing diameters, Fig. 1.
The distance AB will be approximately the pitch. Now describe a
smaller circle for the base of the teeth and halfway between these
circles may be taken as the pitch circle.

Now describe a circle the same size as the largest circle on a
piece of 1/16-in. sheet metal, and having cut it out and filed it
up to this circle, fasten the marked-out paper circle accurately
over it with glue. Saw-cuts can now be made down the diameters to
the smaller circle with the aid of a saw guide, Fig. 2, made from
1/16-in. mild steel or iron. This guide should have a beveled
edge, E, from F to G, to lay along the line on which the saw-cut
is to be made. The straight-edge, CD, should be set back one-half
the thickness of the saw-blades, so that the center of the blade,
when flat against it, will be over the line FG. A small clearance
space, FC, must be made to allow the teeth of the saw to pass.

The guide should then be placed along one of the diameters and
held in position until gripped in the vise, Fig. 3. The first
tooth may now be cut, care being taken to keep the blade of the
saw flat up to the guiding edge. The Model Engineer, London, says
if this is done and the saw-guide well made, the cut will be
central on the line, and if the marking-out is correct the teeth
will be quite uniform all the way round. A small ward file will be
needed to finish off the teeth to their proper shape and
thickness.

In making a worm wheel the cuts must be taken in a sloping
direction, the slope and pitch depending on the slope and pitch of
the worm thread, which, though more difficult, may also be cut
with a hacksaw and file.

A bevel wheel should be cut in the same manner as the spur wheel,
but the cut should be deeper on the side which has the larger
diameter. To cut a rack the pitch should be marked along the side,
and the guide and saw used as before (Fig. 4).

** How to Make Four Pictures on One Plate [46]

Secure two extra slides for the plate holders and cut one corner
out on one

[Illustration: Four Photos on One Plate]

of them, as shown in Fig. 1. Make a hole in the other, as shown in
Fig. 2. With a lead pencil draw on the ground glass one line
vertical and one horizontal, each in the center. This will d