Electric discharge machining apparatus with switch connection between workpiece and mount

An electric discharge machining apparatus for machining a workpiece comprising:

• a processing electrode fed while a predetermined gap is maintained with respect to the workpiece;
• mounting means for mounting said workpiece for machining;
• processing liquid supply means for providing a processing liquid to said workpiece and operative to place said workpiece and mounting means in a processing said liquid environment while said workpiece is being machined by said processing electrode;
• insulating means for electrically insulating said workpiece from said mounting means;
• switch means comprising first and second contacts and a connector selectably joining said contacts, said switch means being removably attached to said mounting means by a rigid connection member which provides an electrical connection from said mounting means to one of said first and second contacts;
• and
• electrical connection means connecting the other of said first and second contacts with said workpiece, said switch means being attached to a position on said mounting means such that the length of said electrical connection means is substantially minimized,
• whereby said switch means is operative to provide an electrical short circuit connection state, through a conducting loop, between said workpiece and said mounting means for a first processing operation and to provide an open circuit isolation state of said workpiece from said mounting means for a second processing operation.

An electric discharge machining apparatus comprising:

• an electrode:
• means for causing electric discharge to occur across a gap defined between said electrode and a workpiece;
• mounting means for holding the workpiece in place;
• insulating means for electrically insulating the workpiece from said mounting means;
• a switch comprising first and second rigid terminal members, said first rigid terminal member having a first stationary contact formed thereon, said second rigid terminal member having a second stationary contact formed thereon, said switch further comprising movable contact means for selectively providing an electrical connection between said first and second stationary contacts, said first rigid terminal member being directly mechanically connected to said mounting means to establish an electrical connection therebetween and said second rigid terminal member being electrically connected to the workpiece.