78 



ARMATURE CONSTRUCTION 



The lower parts of the laminations are spaced by hemispherical 

 projections pressed out from the lamination itself to a height 

 equal to the width of the duct. It may be noted that this 

 construction simply utilises a single core plate on one side of the 

 duct, without introducing any extra pieces. 



FIG. 80. Ventilating Spacing-piece. British Thomson Houston. 



As stated above, cast spacing- pieces are being abandoned and 

 replaced by sheet metal fingers on edge, the variations in the 

 different designs relating principally to the method of securing 

 the sheet metal fingers. 



A method is shown in Fig. 78 in which the fingers are 

 shrouded together with a ring of wire, riveted into a notch in the 



