COMMUTATOR CONSTRUCTION 



121 



In Fig. 135 the mica V-ring is in one piece, fitting over the 

 V of the metal end ring; whereas in Fig. 136 the mica V-ring 

 is made up of two pieces, which wedge up together at the roots 

 of the dovetail in the commutator segments, where a small recess 

 is turned. 



The latter practice is recently becoming customary with 

 several makers, and it is stated that it gives more satisfactory 

 results, and the insulating rings have better insulating properties. 



FIG. 138. Component parts of large Commutator. Dick, Kerr & Co. 



It is said that in some cases where the hitherto common 

 method of Fig. 135 is employed, the mica ring gets strained at 

 the corner of the V when subjected to the pressure during the 

 tightening up of the commutator, and is liable to break in places 

 at the corner of the dovetail. It is further maintained that it is 

 not reasonable to expect such good insulation in a micanite ring 

 with a small radius of curvature as may be obtained with two 

 independent cones. 



Fig. 138 shows a group of the component parts of a similar 



