110 



ARMATURE CONSTRUCTION 



Soft sheet leatheroid or fibre 3 mm. thick, and arranged as shown in 

 Fig. 121, separates the clamping blocks from the copper segments, 

 so that short circuits may be detected by a testing-lamp or magneto 

 bell. These are all mounted together, with 

 the lowest ends of the copper segments and 

 insulations resting upon a horizontal surface 

 plate. For the best results, the copper seg- 

 ments and mica segments, when thus rough, 

 must have their lower ends constitute ap- 

 proximately true surfaces, normal to their 

 outer surface, otherwise the segments when 

 FIG. 123. Showing objec- first loosely assembled will not come into 



tionable and defective ar- j. i T . t -n 



rangement of Segments. even approximately true alignment, but will 

 tend to stand as roughly indicated in Fig. 123. 



After the copper and mica segments are all assembled in place, 

 they should next be squared up true to a steel square which 

 is placed inside on the surface plate, as shown in Fig. 124. 

 When all the segments have been trued up as indicated, the 

 clamping ring bolts should be tightened up, each a little at a time, 

 a quarter or even only an eighth of a turn each time according to 



Surface Piate,. 



FIG. 124. Squaring up Segments. 



the size of the commutator. The distance between the outside of 

 the clamping blocks and the inside of the clamping ring may be 

 gauged by a pair of inside calipers, as indicated in Fig. 125. At 

 this stage great exactness must be obtained, as otherwise the 

 surface will have oval or flat places ; but by frequently calipering 

 the distance between the clamping blocks and the ring, and by 

 taking time in tightening the clamping blocks by but a very little 

 each time, a high degree of exactness may be attained. 



Instead of the arrangement of assembling rings shown in Figs. 

 121 and 122, a method is sometimes used of pressing a single 



