"nesesu" wrote in message
...
On Feb 9, 7:57 pm, DaveC wrote:

After you turned the commutator, did you undercut the mica between the
commutator segments? It is critical that the insulation be below the
surface of the copper to ensure good contact between the brushes and
the copper. If there is still sufficient undercutting [you only
skimmed the surface of the comm] then be sure that there is no copper
shorting between commutator bars. The copper often 'smears' a bit when
being turned and will bridge the gaps here and there. A "pole growler"
will show up any such shorts.

Neil S.


Been there, did that...
My wife's grandmother was the only person I've ever known that wore out an
old Electrolux vacuum cleaner. When the motor was disassembled, there was a
noticeable groove in the commutator. Put it on a lathe and turned it down in
very small steps, finishing off with very fine grit on a wet cloth to smooth
to a near mirror finish. Complete by removing any copper flash that wound up
in the gaps between commutators.

Be careful not to cut too much at a time as the torque drag might twist the
commutator on the shaft. Also watch that you don't get too close to where
the wires are attached to the commutator.

Everything was marked on disassembly to get the orientation correct on
reassembly. If all is right, applying a DC to the motor will cause a
rotation speed equal to the speed when the polarity is reversed. If the
fields aren't aligned to the commutator, it will run faster in one
direction.

With new brushes, worked at least another ten years and Grandma was very
happy.