Ho All,
thanks for your replies.
I've had another look this morning and tried your suggestion Hood - unfortunately, it didn't make a difference.
Gerry,
I don't think it's noise from the steep/direction lines to the stepper drives. I've used a good quality screened pair cable that has been grounded in the middle of it's length.
Tweekie, I've rechecked the setup - I can get a stable and proportional signal on the 0-10v connection. When rapiding, this value increases. e.g. 5v at 1000 rpm. Rapiding increase this to about 7v and 1440 rpm.
I've monitored the 5 and 12 volt supplies with a DVM, and these look rock steady.
Enabling spindle feedback control works - sort of! Ther's a momentary change of speed at the start and end of a rapid movement, while the controller gets a grip. But I feel this is fixing the symptoms rather than the problem....
Has anyone seen this sort of fault before?
Regards,
Paul