The armature of a dynamo (Fig. 84) consists of a steel or iron shaft on which are mounted a large number of thin circular iron disks held together by bolts. This arrangement makes a cylinder with a groove cut in it, running parallel to the armature shaft. Insulated wire is wound around the core and laid in the grooves, which are lined with mica or some other insulating material. The wires are painted over with shellac. Binding wires are wound on the outside to hold the armature coils in place.

Fig. 84.   Armature.

Fig. 84. - Armature.

The iron core or shaft is used in the armature to concentrate the lines of force and to keep them from escaping. The electric current is generated by the rotary motion of the armature between the poles of the magnets.