In plain vertical eroding, the eroded configuration is already dimensionally determined by the shape and dimensions of the electrode. Machining of undercuts is not feasible. The introduction of planetary electric discharge machining has now extended the possibilities of the erosion technique. It is a machining technique featuring a relative motion between workpiece and electrode that is achieved by a combination of three movements, vertical, eccentric and orbital. The planetary electric-discharged machining is also known as the three-dimensional or multi-space technique.
This technique now allows undercuts to be formed in a cavity. A further, major advantage is that, through compensation of the undersized electrode, it is possible to completely machine a mold with just one electrode.
The electrodes are made by turning, milling or grinding, the mode of fabrication depending on the configuration, required accuracy, and material. High-speed cutting can be used to optimize fabrication of graphite or copper.