Figure 7-19.--Undercutting mica with a hacksaw blade.
If a mica undercutter is not available, use hand tools
to cut the mica, as shown in figure 7-19. Do not use a
lubricant. Also, do not widen the commutator slots by
removing metal from the bars, nor leave a thin edge of
Figure 7-18.--Undercutting commutator mica with
mica next to the bars.
undercutter.
After removing the high mica, smooth off all burrs.
The rotary cutters are either U- or V-shaped. The
Then polish the commutator and test. Figure 7-20 shows
U-slots will give long wear and are best suited to
examples of good and poor undercutting.
slow-speed machines or machines that operate in a clean
atmosphere and require little maintenance. The V-slots,
DISASSEMBLY AND REASSEMBLY
which are more quiet than U-slots, are better if dirt and
OF ROTATING ELECTRICAL
dust are present. The proper thickness for a U-shaped
MACHINERY
cutter is equal to the thickness of 0.001 inch. In
When you have to disassemble and reassemble a
general, it is best not to cut U-shaped slots deeper than
large motor or generator, follow the procedures outlined
one thirty-second of an inch, or, at most, three
in the manufacturer's instruction manual, exercising
sixty-fourths of an inch. The V-shaped slots are cut to a
care to prevent damage to any part of the machine. The
depth that will remove some copper at the top.
Figure 7-20.--Example of good and poor undercutting.
7-17
