Two types of EDM (electro-discharge machining) processes are performed; Wire EDM and Sinker EDM.

Sinker EDM is a process typically consisting of a graphite, brass, or copper tube-shaped electrode that is slowly fed into a workpiece that is immersed in oil. A pulsed electrical discharge from the electrode causes sparks to jump to the workpiece, each tearing out a small particle. Oil, also known as cutting fluid, typically flows through the center of the electrode to help flush the particles away from the cutting path. The electrode gradually erodes its way through the workpiece. Surface finishes are typically rougher than in grinding processes, however secondary cuts or slower cutting speeds may improve finish. Tolerances typically range from +/- .001" to +/- .005" depending on the material being cut and the length of the cut (or electrode travel).
 
Ceramic magnets cannot be machined utilizing EDM because the material does not allow for the "electrical arcing" to take place between the electrode and the work piece.
 
Wire EDM is a process very similar to Sinker EDM except the electrode carrying the electrical pulse is a very thin (0.010") zinc-coated brass wire. Whereas the copper electrode gradually disintegrates in Sinker EDM, with Wire EDM the wire electrode simply carries the current to the work piece as it unravels from a spool. With the benefit of the ultra-thin wire, extremely tight tolerances can be held. Surface finishes are similar to Blanchard grinding, however secondary cuts are often made to achieve a smoother finish and even tighter tolerances. Typical tolerances can be held to +/- .0002" to +/- .0005".
 
Just as in Sinker EDM, the work piece must be electrically conductive in order for the EDM process to work. Hard and soft ferrite materials (ceramic magnets) as well as some epoxy-rich bonded magnetic materials cannot be cut utilizing the EDM process. Dexter has both processes in a CNC-capable format for unattended operation.