John, I don't think they make an EDM machine big enough to fit one of those excavators you work on into the fluid it needs to submerge the electrode. Unless things have changed a lot since we got an EDM at the high school machine shop next door to the auto shop I ran for 20-something years, the part has to be immersed in a vat of non-conductive liquid. Ours was set up to cut a 5-pointed star shape through a piece of 1 inch thick steel plate- - - - -pretty impressive!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!