Method and apparatus for adjusting the gap in an electric discharge machine

In an electric discharge machining method comprising defining a working gap between an electrode and a work piece, controlling the feed of said electrode to adjust said working gap and moving said electrode and a work part of said work piece relative to each other thereby giving a satin finish to a surface of said work piece, the improvement comprising the steps of:

• applying across said working gap, repeatedly and consecutively, a series of voltage pulse trains, each voltage pulse train consisting of a plurality of high voltage pulses followed by a single low voltage pulse;
• detecting in response to the application of said low voltage pulse a working current across said working gap, comparing the working current for discrimination with a reference value corresponding to a predetermined interelectrode condition, and controlling the feeding of said electrode in accordance with the compared working current and reference value to adjust said working gap;
• and
• applying said high voltage pulses for a predetermined time to cause discharge and give a satin finish to the surface of said work piece by electric discharge machining.