Abstract: An electro-discharge machining apparatus includes an electrode carrier on which there are mounted a plurality of separate electrodes. A circuit for each electrode applies a high voltage discharge initiating pulse followed by an extended lower voltage discharge sustaining pulse to the associated electrode. A gap voltage sampling circuit samples the voltage between the electrode and the workpiece and a "low wins" circuit passes a signal representing the lowest gap voltage as a feedback signal for a servo-actuator which moves the electrode holder towards and away from the workpiece.

Abstract: An electro-discharge machining apparatus includes an electrode carrier on which there are mounted a plurality of separate electrodes. A circuit for each electrode applies a high voltage discharge initiating pulse followed by an extended lower voltage discharge sustaining pulse to the associated electrode. A gap voltage sampling circuit samples the voltage between the electrode and the workpiece and a "low wins" circuit passes a signal representing the lowest gap voltage as a feedback signal for a servo-actuator which moves the electrode holder towards and away from the workpiece.