volve easily, but not too loosely. The slots allow an adjustment, the
screws, S, holding T to U. The shaft rests in a dent made in a piece of
tin which is tacked to A. The yokes are elsewhere described.

[Illustration: Fig. 119.]

264. Field-Magnets. In this model they were made of 5/16 bolts, 2 in.
long, placed 2 in. apart center to center. The washers are 1-1/8 in.
apart inside. (See App. 88 for full directions.) App. 89 and 71 should
be studied. Except in size, they are made as in App. 144. They have 8
layers of No. 24 or 25 wire.

265. The Armature, Fig. 121, on this style of motor consists of a
regular horseshoe electro-magnet, made in the same general way as the
field-magnets. The electro-magnets, 12 and 16, are smaller, however,
than the field-magnets. The cores are 1/4 in. stove-bolts, 1-1/4 in.
long under the head. They are placed 2 in. apart, center to center. They
are insulated and wound as fully explained in App. 88. These 1/4 in.
bolts require a change in your winder. (See App. 147 for this.) If you
wish to use 5/16 bolts, you may use the same axle for your winder as
before. The washers are 5/8 in. apart, inside. The cores are wound with
4 or 6 layers of No. 24 or 25 wire. This makes them about 3/4 in. in
diameter. They are held in a tin yoke, 14, made of 5 or 6 thicknesses of
tin. 14 is 3 x 3/4 in., and has 3 holes punched in it. The two outside
holes are 2 in. apart. Through these pass the bolts, which are held
firmly by the 2 nuts. The shaft, S B, is a sink-bolt, 3 in. long, and
1/4 in. in diameter. (See Sec. 253.) The inside ends (Sec. 123) of the
coils should be firmly twisted together or held under the top nuts to
make a good connection between them.

[Illustration: Fig. 120.]

266. The Commutator is in two parts, which must be insulated from each
other. The 2 sections are made out of thin tin or copper in the shape of
an inverted T, as shown at 10, Fig. 121. The arms of the T are about
3/8 in. wide, the horizontal ones reaching about half around the spool,
E. The vertical arm reaches over the top of E, and is held down by a
small screw, J. The sections, 10, must not touch the shaft. The outside
wires (Sec. 123) of 12 and 16 are fastened under these screws, J, and
they must not touch the shaft. Bend the tin sections so that they will
be as nearly round as possible. The spool, E, has been sawed off so that
it will go between the field-magnets. Wind paper around the shaft to make
it fit solidly int