Spark discharge maching apparatus for hard metals

Claim 1

ELECTRIC SPARK DISCHARGE MACHINING APPARATUS INCLUDING, IN COMBINATION WITH A METAL WORK PIECE, COOPERATING ELECTRODE ESTABLISHING A SPARK DISCHARGE GAP WITH SAID WORK PIECE, MEANS IMMERSING THE OPPOSING SPARK DISCHARGE SURFACES OF THE ELECTRODE AND WORK PIECE IN MACHINING FLUID, AND MEANS TO EFFECT RELATIVE FEED MOVEMENT BETWEEN THE ELECTRODE AND WORK PIECE AS MACHINGING PROGRESSES; AN ENERGY STORAGE CAPACITANCE, A SOURCE OF ENERGY FOR CHANGING SAID CAPACITANCE, A CHARGING CIRCUIT SERIALLY INTERCONNECTING SAID SOURCE AND CAPACITANCE, AND A DISCHARGING CIRUCIT INCLUDING ELECTRICAL CONDUCTORS CONNECTING SAID ELECTRODE AND WORK PIECE GAP ACROSS SAID CAPACITANCE, WHEREBY THE CAPACITANCE INTERMITTENLY CHARGES FROM SAID SOURCE AND DISCHARGES ACROSS SAID GAP, SERIES RESISTANCE THERIN PROLONGING THE DISCHARGE PERIOD OF SAID CAPACI-TANCE JUST SUFFICIENTLY THEREBY TO REMOVE SUBSTANTIALLY THE SHORT-CIRCUITING MOUDS INHERENTLY PRODUCED BY SUCH DIS CHANGE ON THE MULTULLY OPPOSING SURFACES AND WHICH OTHERWISE SUBSTANTIALLY REMAIN THEREON AFTER THE DISCHARGE WITHOUT SUCH PROLONGATION OF THE DISCHARGE PERIOD.