PARTS OF A DYNAMO-ELECTRIC MACHINE 53 



In taking up the construction of the commutator we 

 shall consider the bars themselves, the insulation used in 

 the commutator, and the commutator spider, which serves 

 to clamp the bars together and hold them on the armature 

 shaft. 



Form of bars. The bars themselves are always made 

 of copper, because it is a good conductor, is easy to shape 



FIG. 27. Commutator for Large Railway Generator, Showing Form 

 of a Spider. The commutator and armature here shown are com- 

 pletely assembled. General Electric Co. 



properly, and wears well. Generally these bars are 

 stamped from copper rods, the cross-section of the rods 

 being trapezoidal so that as the bars are assembled side 

 by side they form a cylindrical ring. The bar for a medium 



