There is a design for home made edm put out by HSM Home shop Machinist Magazine with a stepper driven servo ram. There are two types of EDM one is wire and the other is by electrode die, Both work on the same principal of a DC (90 volts or so) pulsating voltage with the Work at positive potential the Neg Electrode in the shape of the item you want to cut out is advanced to the work and an arc is drawn causing an erosion of the work piece, the electrode will keep on advancing maintaining about 5 thou clearance between the electrode to maintain the arc. The electronics sense whenever the gap is too large or if the electrode touches (shorts) to the work.
The work is usually kept under a special liquid, home made operators some times use ethylene glycol.
This differs from a 'Tap Disintegrator' used for removing broken taps from expensive castings etc. these work in similar fashion, but use low voltage 6 to 12 v AC high current and the resulting arc burns away both the sacraficial electrode and the offending tap. EDM is a finer, more precise than Plasma and is used to make press dies etc or to 'machine' very delicate objects like surgery tools etc. BTW the die electrode is usually made from a graphite material.
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.