320 ARMATURE CONSTRUCTION 



several per slot), the coils are formed on a simple bobbin block 

 similar to the bobbins used for rectangular field coils. 



Figs. 392 and 393 illustrate suitable formers for straight and 

 bent coils. 



With form-wound coils wide-open slots are necessary, and the 

 question of open v. semi-closed or tunnel slots is not simply 

 dependent on the first cost of winding. 



FIG. 391. Strip- wound Armature (Bruce Peebles). 



So far as first cost goes, the form-wound coil is undoubtedly 

 considerably cheaper, but hand winding possesses superiority in 

 other respects. Prominent among these is the matter of slot 

 insulation. With open slots and form-wound coils the slot 

 insulation must take one of the forms shown in Figs. 394 to 397. 

 Each of these has the drawback that the insulating tube has a 

 joint in it, and at this point the insulation is weak. 



This is of considerable importance in high -voltage machines, 

 but with low-voltage machines having one or two conductors per 



