Method of controlling electrical discharge machining

Claim 1

In a method of electrically machining a workpiece in which a tool electrode is spacedly juxtaposed with the workpiece across a dielectric-filled machining gap, the electrode can have a multiplicity of geometrically different contours including ridge, edge, indent an planar configurations, and a series of electrical machining discharges are applied to the gap to remove material from the workpiece, the improvement which comprises the steps of: determining values for a first parameter of electrical discharge across the gap the levels of this parameter being characteristically determined by the respective configuration and being sufficiently different from one another to enable detection of the respective level to discriminate between said configurations; establishing respective threshold levels for said first parameter corresponding to the determined values; detecting the said first parameter during a machining discharge and comparing the detected parameter with said threshold levels; and regulating a second parameter of the latter discharge in a respective one of a plurality of predetermined modes respectively corresponding to said threshold levels upon the detected first parameter attaining a respective threshold level to establish a corresponding value of said second parameter to the end of the said machining discharge.