Machining laminations and testing for shorts 1

[UKpete]

We have an active magnetic bearing assembly (on a large motor) with a shaft "journal" consisting of a pack of 0.2mm laminations. These laminations are washer shaped, clamped between supporting plates and the whole pack is a shrink-fit on the shaft. It is subsequently machined to maintain concentricity and circularity and give the required airgap.

My questions are:
1. does anyone have any recommendations on how to machine the surface of the lamination pack without shorting them together.
2. having done this machining, what method could be used to test for shorted laminations?
3. when shorted laminations are found, how might they be treated?

I have done a search on Eng-Tips but suprisingly (in view of the fact that repairing rotor rubs must be common practice) the subject doesn't seem to have been covered here before - any input on any of the above questions gratefully received.

 

[sreid]

I like the eddy current scanning idea-wish I had thought of it. If it works out, Launchpoint sells a cost effective eddy current sensor that they use in their magnetic bearings (approx. $1000 USD).

http://www.launchpnt.com/eddy_sensor.htm