FIG. 17.—The completed Armature showing how the Commutator is constructed.
The armature should not scrape against the field at any point, but should clear it by about one-sixteenth of an inch.
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.
The completed motor is shown in Figure 19.
One end of the 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.
The motor, being of the two-pole armature type, must be started when the current is turned on, by giving it a twist with the fingers.
FIG. 18.—Details of the Commutator.