On Fri, 17 Jun 2005 07:39:55 -0700, Eric R Snow
wrote:

Snip


Jim, I have a demagnetizer. The thing is, when parts are ground on an
electromagnetic they stick when power is removed. All the chuck
controls I've used have a demagnetizing button that helps to get the
part off the chuck. I have seen chuck controls without this feature
but have never used one. Maybe that's why chuck controls are so
expensive? It's because of the demagnetizing electronics?
Thanks,
Eric

I've never used one of these chucks so I can't be sure how
they're organised. Thoroughly demagnetising a workpiece on an
electromagnetic chuck would need a sequence of decaying amplitude
polarity reversals. This is could be carried out by sequencing two or
three Triacs or SCRs. Possibly a pair to control polarity reversal and
one to program the amplitude - sounds a bit expensive.

One posible kludge is to remember that much of the remanent
magnetism is a fixed amount as it originates from hysteresis in the
chuck iron. If this were entirely true (OK with mild steel workpiece -
not OK with a large lump of alnico) a carefully chosen single pulse of
reverse polarity would be enough to unstick the workpiece.

Don't know enough about your chuck to tell you how much but a
lot less than 100v - start with only a few volts and increase it bit
by bit until it does the job.

Don't forget to be certain that the chuck body is properly grounded.
Used dry, the insulation failure hazard is about the same as with an
electric motor. However, if you're going to use it wet with suds
coolant I second comment that an isolation
transformer is a sensible addition

Jim