What is overcut in EDM, and how does it affect part dimensions?

Overcut is the radial clearance between the physical electrode surface and the cavity wall. Because electrical sparks jump across a finite distance, the burned cavity is always larger than the electrode geometry. Electrodes must be manufactured undersized by the exact overcut dimension per side. Higher gap voltages, higher amperages, and dirty dielectric fluid increase overcut width. In addition, sharp electrode corners always produce a small corner radius in the cavity matching the spark gap length.