ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 15 
and packing as well as that of erection has specially to 
be taken into account, and accordingly the overall dimen- 
sions of the largest part, or the weight of the heaviest 
piece, will be in many eases limited, and such limits have 
therefore to be carefully considered by the designer. 
30. Method of Building.—Experience has shown that heavy 
castings are liable to alter their shape if machined in any 
other position than the final one. For upright machines, 
the frame is turned in a vertical position and all necessary 
care must be taken to avoid any alteration of the true 
Fig. 8.—SECTIONAL VIEW OF ARMATURE FRAME FOR 
LARGE ALTERNATORS. 
shape of the armature. If the shape is not true a mag- 
netic pull will take place due to the eccentricity. 
In placing the sheet stampings of the core into the cast 
iron frame of the armature, care must be taken that the 
latter is clamped down on an accurate floor plate, until 
the core is ready to receive the coils. This method pre- 
vents the armature from altering its true shape under the 
effect of the bolts which compress the core plates together. 
The stampings are of soft sheet iron or steel of the highest 
permeability, the choice of this material having an im- 
portant influence on the efficiency. The plates are about 
