utator is turned from a piece of brass pipe, 3/4 in.
inside diameter, as shown in Fig. 6; The piece is placed on a
mandrel and turned to 3/4 in. in length and both ends chamfered to
an angle of 60 deg. Divide the surface into 12 equal parts, or
segments. Find the centers of each segment at one end, then drill
a 1/8-in. hole and tap it for a pin. The pins are made of brass,
threaded, turned into place and the ends turned in a lathe to an
outside diameter of 1-1/4 in. Make a slit with a small saw blade
in the end of each pin for the ends of the wires coming from the
commutator coils. Saw the ring into the 12 parts on the lines
between the pins.

The two insulating ends for holding these segments are made of
fiber turned to fit the bore of the brass tubing, as shown in Fig.
7. Procure 12 strips of mica, the same thickness as the width of
the saw cut made between the segments, and use them as a filler
and insulation between the commutator

[Illustration: Armature-Ring Core, Its Hub and the Construction of
the Commutator and Its Insulation]

bars. Place them on the fiber hub and slip the hub on the shaft,
then clamp the whole in place with the nut, as shown in Fig. 3.
True up the commutator in a lathe to the size given in Fig. 6.

The brush holder is shaped from apiece of fiber, as shown in Fig.
8. The studs for holding the brushes are cut from 5/16-in. brass
rod, as shown in Fig. 9. The brushes consist of brass or copper
wire gauze, rolled up and flattened out to 1/8 in. thick and 1/4
in. wide, one end being soldered to keep the wires in place. The
holder is slipped on the projecting outside end of the bearing, as
shown m Fig. 3, and held with a setscrew.

The field core is insulated before winding with 1/64-in. sheet
fiber, washers, 1-1/8 in. by 1-1/2 in., being formed for the ends,
with a hole cut in them to fit over the insulation placed on the
cores. A slit is cut through from the hole to the outside, and
then they are soaked in warm water, until they become flexible
enough to be put in place. After they have dried, they are glued
to the core insulation.

The field is wound with No. 18 gauge double-cotton-covered magnet
wire, about 100 ft. being required. Drill a small hole through
each of the lower end insulating washers. In starting to wind,
insert the end of the wire through the hole from the inside at A
Fig. 1, and wind on four layers, which will take 50 ft. of the
wire, and bring the end of the wire out at