COMMUTATOR CONSTRUCTION 



119 



purposes is to be recommended. The temporary external clamping 

 rings, bolts, and segmental plates should be of the most massive 

 construction, as roughly indicated in Figs. 121 and 122. This 

 should also be the case with the permanent end rings and the 

 commutator spider. The depth of the copper segment should be 

 very liberal, not with a view to permitting repeated turning or 



FIG. 136. Typical Commutator Construction. for large Traction Dynamo. 



grinding of the commutator surface (this becomes superfluous in 

 good designs), but with a view to mechanical strength. The 

 radial depth of copper below the inner corners of the end 

 clamps should, therefore, be very liberal. The segments should 

 be repeatedly and vigorously tapped during the application of 

 the pressure and the heating. A construction with a massive 

 commutator spider projecting from the armature spider is to 

 be preferred, both on account of the superior ventilation and 

 of the relative rigidity of armature conductor and commutator 

 segments. A good modern construction on these lines is indi- 

 cated in Fig. 135. Fig. 136 shows an alternative construction 

 for large commutators. Unlike the construction of Fig. 135, 



