On 2/11/2012 1:15 AM, 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.

Thanks for that info.

I did not undercut mica. I presumed that since, before turning on the lathe,
the motor was functioning well enough (sans bearing noise) with not-undercut
mica that its purpose was not important.

What's the best way to undercut? Using an exacto or utility knife in my hands
gets quickly messy...

I looked closely and eliminated any segment shorts on the commutator.

Thanks,
Dave


Using a hacksaw blade the idea is to grind off the 'set' on the teeth to
a thickness that will be smaller than the commutator bar gaps.
Then it is used by having the teeth point backwards towards you, the
action is then pulling rather than pushing which IMHO gives more control.
Whilst doing this try to hold the blade at an angle so that it cuts
against the sides of the bars, usually you can see the material flake
off when done correctly. This is important as it removes any insulation
that might be on the side of the gap you are creating and then can
interfere with brush contact.
While grinding the blade snap off the end and make it about 45deg away
from the teeth to make it easy to get to the insulation at the
connection end.
However I doubt the commy is your problem :-)

Rheilly P