The Diseases Of Electrical Machinery 1904
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12
THE DISE ASES OF
taken from the commutator surface with a sharp
pointed tool, after which the surface should be polished
with fine glass-paper.*
If the process has proceeded still further, it may
so happen that the machine will not work, i.e. gives
no voltage, since the contact between the brushes and
the commutator is broken by the protruding mica
insulation.
Turning down. of Commutators.—It may be
here advisable to say a few words regarding the turn-
ing down of commutators. When turning down the
commutator, the author recommends that the peri-
pheral speed should not be greater than 20 to 25 feet
per minute. A sharp pointed tool should be used for
the first cut, so that the mica and copper are turned
down together, and that no mica segments should
remain sticking out. For the finishing cut a similar
tool should be used, and it should not traverse at a
greater rate than inch per revolution. The
cutting speed may, however, be raised to 35 feet per
minute. The commutator must then be carefully ex-
amined on the lathe, to see whether any of the segments
are joined by tags or burrs of copper. These must be
carefully removed. The surface must then be smoothed
with glass-paper, and as good a polish given as pos-
sible, for which purpose the use of a few drops of oil
* [A less drastic remedy than taking a cut off the commutator, is to
file the surface while it is gently turned round, using a glass-hard file,
itself of fine cut. Or instead of a file, a fine carborundum hone may be
applied.—Ed.]