ull directions.) The bolt
cores are 2 in. apart, center to center. (See App. 89.) The tin yoke, D,
is made like App. 71, and it is fastened to the base, like App. 90. The
hole for the screw, however, is made a little to one side of the center,
so that a dent can be made at the center for the bottom of the shaft, 8,
to turn in. Make the dent with a center punch. The yoke is fastened to
B, so that one edge of it is 1-1/2 in. from the back edge of B. (Fig.
116).

252. The Armature, A, is made of 6 or 8 thicknesses of tin, 2-1/2 in.
long and 3/4 wide. (See App. 71.) In its center is punched or drilled a
1/4 in. hole, so that it can be slipped onto the 1/4 in. "sink-bolt," 8.
If you have taps you can make the hole a little smaller than 1/4 in.,
and thread it so that it will screw onto 8. A must be heavy enough to
revolve a few times when once started. It is pinched between two nuts, 9
and 11, so that it just clears the poles when it turns. (See App. 145
for another form of armature.)

[Illustration: Fig. 116.]

253. The shaft or axle, 8, is made of a "sink-bolt" that is 3 in. long
and 1/4 in. in diameter. These sink-bolts are threaded over their entire
length, and are furnished with two nuts, 9 and 11, Fig. 117. File or
grind the end of 8 to a point, so that it will turn easily in a dent
made for it in the yoke, D, or in a dent made in another piece of tin
fastened over the yoke. The shaft is held in a vertical position by the
arm, C.

254. The Arm, C, is made of 2 or 3 thicknesses of tin. It is 3 x 3/4
in.; it has in one end a hole for the shaft to revolve in easily, and in
its other end a slot is cut. A screw-eye and bur are used to hold C to
the upright, U. By this means the shaft can be moved and regulated as to
position.

[Illustration: Fig. 117.]

255. The Commutator, 9, (Fig. 117), is made of one of the nuts furnished
with the shaft. Two of its corners are filed or ground off, so that it
has the shape shown at the right, in Fig. 117. The copper wire, 10, rubs
against 9, as the pointed part of it comes around. 10 is really a
"brush," and carries the current into 9 at the right time.

256. Connections. Join the two inside ends (Sec. 123) of the coils to 4.
The outside end of 2 is joined to X; the outside end, 7, of the other
coil, 6, is carried up under or around the screw-eye, S I, and then its
bare end reaches out and gently scrapes against the top of the shaft, 8.
The wire, 10, leads from Y to the back of th