Beege wrote:

On an old Acroloc, we had a rumble in "Y". Solved it by cleaning the
tachometer brushes. They were at the rear of the drive motor. Ten years ago.
Memory fades...


Well, I've never been inside an SEM motor, so I don't know what sort of
tach brushes they use in there. I'm pretty sure it is a traditional DC
brush
tach. The silver wire brushes usually don't need any attention until the
completely wear in two, and then cleaning won't be much use. Cleaning
them before that point would require nothing harder than a stream of
alcohol, as the wires are hair thin.

This one definitely sounds like a servo loop problem, and the Bridgeport
guy has been out several times at $500 a pop to do the same thing.

Jon