96 



ARMATURE CONSTRUCTION 



ing away from the core, through which a pin is driven into a hole 

 drilled in the shaft ; or the flanges may be in this case secured by 

 a grub-screw set in the boss. In shafts of any size it is, of course, 

 inadvisable to drill a hole through the shaft, and hence this plan 

 should not be employed. 



Fig. 104 shows a good construction for rotors of moderate size. 

 In this case the spider consists of a cast-iron boss with four radial 

 arms, which project to the internal periphery of the stampings, 



r 



FIG. 103. Drawing showing Typical Construction for small Rotor 



the latter being secured to the arms by means of a square key ; 

 this engages in a key-way, milled longitudinally along the face of 

 one of the arms, and a key-way punched at the internal surface of 

 the stampings. The core is drawn up together between a pair of 

 end flanges which are exactly similar, and may be cast from the 

 same pattern, by means of four bolts which just clear the inside 

 of the stampings. As a matter of fact, most of the methods of 

 drawing up end flanges and securing stampings to the spider arms 

 shown in Chap. III. may be used in this connection also equally 

 well. A point to be noted about the construction in Fig. 104 is 

 that there is no external cylindrical shell connecting the outside 



