Ques. What provision is made for shifting the ring to adjust the lead?
Ans. The ring is rotated by means of a worm gear and hand wheel.
CHAPTER XXII
ARMATURE CONSTRUCTION
The armature of a dynamo has been defined as: a collection of coils of wire wound around an iron core, and so arranged that electric currents are induced in the wire when the armature is rotated in a magnetic field.
From the mechanical point of view the armature may be said to be made up of the following parts:
1. Shaft;
2. Core;
3. Spider
(in large machines);
4. Winding;
5. Commutator
(broadly speaking).
Of the two types of armature, ring and drum, the latter is almost universally used, hence the examples of construction which follow will be confined chiefly to this type.
Shaft.—A typical armature shaft is shown in [fig. 349]. It is made of steel and, except in the smaller machines, is thicker in the middle than at the ends for stiffness to withstand the strong magnetic side pull on the core when the latter is slightly, nearer one pole piece than the other.
Ques. What is the object of providing shoulders on the shaft as in [fig. 349]?