Phil
I was thinking it was your spindle motor, the filter I have is three phase, its meant for the AC servo drives I have, although likely it could be used single phase as well. I may have another filter that my Beaver mill came with, there was one on each motor and as I only have the original coolant and knee motors and have done away with the spindles induction motor I should have it kicking around in the store, will look it out tomorrow if I remember.
Hood