The wire used for winding both the armature and the field should be No. 25 or No. 26 B. & S. gauge double-cotton-covered.
In order to wind the armature, cut off about five feet of wire and double it back to find the center. Then place the wire diagonally across the center of the armature so that there is an equal length on both sides. Place a piece of paper under the wire at the crossing point to insulate it. Then, using one end of the wire, wind four layers on half of the armature. Tie the end down with a piece of thread and wind on the other half.
The ends of the wire are cut and scraped to form the commutator segments. Figure 246 shows how this is done.
Bend the wires as shown so that they will fit closely to the paper core. Bind them tightly into position with some silk thread. Use care so that the two wires do not touch each other. Cut the free ends of the wires off close to the core.
When finished, the relative positions of the armature and the commutator should be as shown in Figure 248.
The brushes are made by flattening a piece of wire by a few light hammer blows.
The brushes are fastened under a small clamp formed by a strip of tin held down at each end with a wood screw. They can be adjusted to the best advantage only under actual working conditions when the current is passing through the motor. One or two dry cells should be sufficient to operate the motor.
Fig. 249.—Details of the Motor.
One end of the field winding is connected to one of the brushes. The other brush and the other end of the field form the terminals to which the battery is connected.