PARATUS 145.

_259. Armature for Motors._ Fig. 118 shows another form of armature that
may be used for small motors like App. 144; in fact, you may find that
this form is easier to make than that of App. 144. M is a 5/16 machine
screw, 1-1/2 in. long, 9 being the nut furnished with it. 9 is filed as
explained in Sec. 255, and forms the commutator. C is the arm (Sec.
254). A is the armature (Sec. 252). A is held firmly in place between
the spool, E, and 9. S is a set-screw which passes through E, and holds
the piece of 1/4 in. dowel, F, in place. N is a needle-point fastened
in the end of F. N revolves in a dent made in a piece of tin, H, which
rests upon a wooden strip, G. G is cut away on its underside, so that
it will straddle the yoke, D, Fig. 117; it is nailed to the base. This
is given as a suggestion. By making F a little longer, N can turn in a
dent made in the yoke, below G.

260. Adjustments. M, being 5/16 in. in diameter, will screw solidly into
the hole in E. Place 9 upon it first, then A, and screw it about 1/2 way
into E. 9 will serve as a lock-nut by turning it so that it will pinch A
and hold it firmly against the top of E. F should reach half way into E.
Put N in place after you have H and G arranged. You can then cut the
upper end of F at such a place that it will bring A about 1/8 in. from
the top of the magnet-cores. Paper wrapped around F will make a good fit
in E. The current should enter M and leave 9, as fully explained in App.
144. (See Sec. 257).

APPARATUS 146.

_261. Electric Motor._ Fig. 119, 120, 121, 122. Fig. 119 shows a front
view, and Fig. 120 a side view of the whole motor. Fig. 121 shows the
part that revolves, and includes the shaft, armature and commutator.
Fig. 122 shows a section of the commutator. All the dimensions are taken
from a model. You can modify the size to suit.

262. Wood-work. The base is 7 x 5 x 7/8 in. The uprights, U, are 3-1/2 x
1 x 3/4 in. They are screwed or nailed to the base from below, their
1-in. sides being towards you in Fig. 119. They are 4-1/4 in. apart,
inside, in this model. The piece, A, is 2-1/2 x 7/8 x 5/8 in., and is
cut away on the underside to straddle the yoke. Fig. 118 is a
suggestion as to its shape. A is screwed or nailed to B.

263. Tin-work. The horizontal arm, T, is made of 3 thicknesses, and
holds the shaft in a vertical position. T is 6-1/4 x 3/4. In its ends
are slots, and in its center is a hole so that the 1/4 in. shaft can
re