This creates craters in both electrodes, the size of which are related to the energy of the spark. Thus, a distinction is drawn between roughing with high impulse energy and planning. The multitude of discharge craters gives the surface a distinctive structure, a certain roughness and a characteristic mat appearance without directed marks from machining.
The debris is flushed out of the spark gap and deposited in the container. Flushing can be designed as purely movement-related operation. This type of flushing is very easy to realize since only the tool electrode, together with the sleeve, has to lift up a short distance. The lifting movement causes the dielectrice in the gap to be changed. Admittedly, this variant is only really adequate for flat cavities. For complex contours, pressure or suction flushing by workpiece or tool electrodes would need to be superimposed.