Method for making a tool electrode for electrical discharge machining

A method of machining a tool electrode for use in electrical discharge machining, the method comprising:

• a. using a preformed model (1), of a shape which is a positive or negative replica of a shape which is to be machined by the tool electrode (6), to produce a positive casting (3) and a negative casting (2) of said shape one of the castings comprising at least on its surface (31) which defines said shape, abrasive material and bonding material which holds the abrasive material in place, and the other comprising a material which is readily machinable and which is stable as regards retaining a shape to which it is machined;
• b. using the said one casting to abrade the other casting by moving the two castings together so that the positive one enters the negative one and, at the same time, applying a relative circulating but non-rotating movement, as defined herein, to the two castings whereby the said other casting assumes dimensions which deviate from what they were before;
• c. making use of said other casting as thus shaped by abrasion for moulding a master mould which, at least on its surface which, allowing for the dimensional deviation, defines said shape, comprises abrasive material and bonding material which holds the abrasive material in place;
• and
• d. using said master mould (5) to abrade a workpiece from which said tool electrode (6) is to be made, and hence forming the tool electrode, by moving the master mould and the workpiece together so that one enters the other and, at the same time, applying a relative circulating but non-rotating movement, as defined herein, to the master mould and the workpiece, the amplitude of said circulating but non-rotating movement being adjusted to give predetermined dimensions of the tool eletrode in relation to those of said model.