Method and apparatus for making a tapered thread

Claim 1

THE METHOD OF MAKING A TAPERED THREAD ON A WORKPIECE COMPRISING PROVIDING A WORKPIECE HAVING A TAPERED SURFACE, PROVIDING A THREADED NON-ERODIBLE CATHODE DIE HAVING A HELICAL THREAD THEREON, THE THREADED PORTION OF SAID DIE BEING SUBSTANTIALLY LONGER THAN THE SURFACE TO BE THREADED AND ARRANGED AT SUBSTANTIALLY THE SAME TAPER AS THE THREAD TO BE FORMED, COATING ALL BUT THE CREST OF THE THREAD OF SAID DIE WITH AN INSULATING MATERIAL, TELESCOPING THE CATHODE DIE AND WORKPIECE ONE WITHIN THE OTHER WITH THEIR SMALL ENDS FACING IN THE SAME DIRECTION UNTIL THERE IS A SMALL UNIFORM SPACE BETWEEN THE DIE AND TAPERED SURFACE OF THE WORKPIECE TO BE THREADED, THEN CAUSING HELICAL MOTION BETWEEN SAID DIE AND WORKPIECE WHILE FLOWING AN ELECTROLYTE THROUGGH THE SPACE BETWEEN THE WORKPIECE AND THE DIE, AND AT THE SAME TIME CAUSING A SUBSTANTIALLY CONSTANT DIRECT CURRENT TO FLOW BETWEEN SAID WORKPIECE AND SAID DIE.