"Bert Hickman" wrote in message
...


However, much of the above is moot since most EDM'ing is done under a
dielectric fluid using actual mechanical contact and high pulse currents
to "blast" away the small areas that make contact as the working
tool/wire is slowly advanced into the work piece.

NO physical contact, Bert. Ever. Physical contact and a short circuit, or
even an arc that lasts more than a few milliseconds, usually will destroy
the workpiece and/or the electrode. As I said, servomechanisms are employed
to keep the gap somewhere in the range of 0.0002 in. - 0.005 in., more or
less, depending upon the other operating conditions. Fine finishes are
obtained at gaps of less than a thousandth of an inch.

EDM as we know it today is indeed run in a liquid dielectric, but the
precursors to EDMs, called "tap busters," used air. These machines are still
made. I don't know who's in the business today but two of them that were
around at least through the '80s were Electro-Arc and Camman. Maybe there is
some info about them on the web that would tell you their operating
voltages.

In my shop we had a crude air-dielectric tap buster sold by Do-All. It had a
240V transformer, but it's not a good example because it had no automatic
servo. It often *did* achieve contact, but it didn't matter, because we
weren't trying to machine accurately, as one does with an EDM machine today.

I just looked at the parameters published for some currently-marketed
ram-type EDMs, and I see that open-circuit voltages fall into the range of
50V - 300V, which is about where they have been since the beginning. These
machines use a light mineral oil for dielectric.

Also, wirecut EDMs, which use deionized water for dielectric, seem to run
around 90V open-circuit.

Ed Huntress