Method and apparatus for electrochemical milling

Claim 1

IN A METHOD OF REMOVING METAL FROM AN ANODIC WORKPIECE AND TO A PREDETERMINED DEPTH UNIFORMLY THROUGHOUT AN UNCOATED SURFACE AREA WHICH IS DEFINED BY AN ACID-RESISTANT DIELECTRIC COATING EDGE AND WHICH IS IMMERSED IN AN ACID ELECTROLYTE WITH A COOPERATING CATHODE MEMBER, THE STEPS OF: (A) COVERING A CATHODE MEMBER WHICH HAS A SURFACE AREA CONTOURED TO CORRESPOND TO THE WORKPIECE UNCOATED SURFACE AREA WITH AN ADHERING ACID-RESISTANT DIELECTRIC COATING, (B) PROVIDING SAID CATHODE MEMBER COATING WITH A SCRIBED LINE HAVING A CONFIRGURATION WHICH CORRESPONDS TO THE WORKPIECE COATING EDGE BUT WHICH IS UNIFORMLY SET INWARD A FIRST PREDETERMINED DISTANCE IN A DIRECTION PARALLEL TO THE WORKPIECE UNCOATED SURFACE AREA, (C) REMOVING SAID CATHODE MEMBER COATING FROM SAID CATHODE MEMBER WITHIN SAID CATHODE MEMBER COATING SCRIBED LINE, AND (D) AFTERWARDS LOCATING THE CATHODE MEMBER IN FIXED RELATION WITH RESPECT TO THE WORKPIECE WHEREBY THE UNCOATED SURFACE AREA DEFINED BY SAID CATHODE MEMBER SCRIBED LINE IS CONCENTRIC WITH THE WORKPIECE UNCOATED SURFACE AREA BUT IS UNIFORMLY SPACED-APART FROM THE WORKPIECE UNCOATED SURFACE AREA A SECOND PREDETERMINED DISTANCE IN A DIRECTION NORMAL THERETO.