From: none@none.com99   
      
   I've got a book around here somewhere on making a simple EDM sinker for   
   burning out broken taps and bolts, but from what I understand the   
   electrode is eaten up as is the material.  So far I haven't broken off a   
   tap in something I couldn't recover that was so precious as to be worth   
   a day or 3 making such a contraption.  Well, not since i bought the book   
   anyway.   
      
   Those type machines typically use a copper rod or copper tube.   
      
   It is my understanding that complex difficult to machine parts (square   
   inside corners) are sometimes made by EDM using a machined graphite   
   electrode. How quickly is that electrode eroded?  Does it erode.   
   Somewhere bouncing around in my head I have some misconglomeration of   
   thoughts telling me I might have heard or read about using graphite   
   electrode EDM for making mold cavities.  Now I have no intention of   
   starting an EDM shop, but I am curious about the process.  I often have   
   customers send me jobs (most I turn or explain away) that want sharp   
   inside corners in a mold cavity.  A lot of them I can explain that if   
   they can live with a tiny radius I can do it, but if it has to be sharp   
   I can't, because or course its never for something with a flat bottom   
   that I can broach.   
      
   I'm not sure I even have a grasp on what questions to ask.  When I turn   
   somebody away I like to be able to suggest to them where to look for   
   somebody who can solve their problem.   
      
   I have seen some amazing videos of sinkers, and wire EDM, but I'm not   
   sure I've seen anything do what I am thinking of.  Sinking a positive   
   into a piece of stock and getting a matching cavity.   
      
      
      
      
   --   
   Bob La Londe   
   CNC Molds N Stuff   
      
      
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