From: muratlanne@gmail.com   
      
   "Richard Smith"  wrote in message news:m134lug3zn.fsf@void.com...   
   ...   
      
   Anyway, I was thinking how it might be possible to produce a flat   
   surface.   
      
   In the steelworks labs. there was the "swing-grinder" which had a   
   vertical spindle and you swung it back and forth over a sample in the   
   chuck, lowering it a bit per pass to produce a flat surface to start   
   going through the finer and finer emery grits with until you could   
   diamond-polish it to mirror finish.   
      
   I thought of base and column of a bench-drill, clamp a collar on the   
   pillar at height of finishing plane, and have angle-grinder on an arm   
   you swing back and forth.  Letting the grinder ride-up for light   
   "cuts", but eventually stopping at the plane dictated by the collar   
   locked to the pillar (column).   
      
   Anyone got a better idea / know how it should actually be done - if at   
   all?   
      
   Regards,   
   Rich S   
      
   ----------------------------   
   I've ground surfaces quite close to shape freehand with an angle grinder by   
   mounting them free to rotate and controlling the rotation speed vs grinding   
   rate by the position of the grinding disk. An example is the front   
   motorcycle tire for my sawmill which needed a wider crowned flat for the   
   bandsaw blade. The sawmill frame helped hold the grinder steady enough to   
   avoid high spots. I used the rear wheel as-is since the previous owner had   
   worn it to the cords burning rubber in the street, and the crown was   
   perfect. The blade was tracking centered after less than 15 minutes of   
   adjustment.   
      
   When grinding the end a straightedge shows if you are grinding concave or   
   convex. Touching the disk to both sides somewhat off the center of the work   
   makes it rotate slowly and guides the disk to cut pretty flat despite its   
   wear.   
      
   A variation is grinding the broken end of a drill bit or endmill square   
   freehand by rotating it against the wheel before adding the drill point   
   angle. I buy high quality dull or chipped endmills very cheaply second-hand   
   and regrind them for roughing, saving the new ones for finish cuts.   
      
   Holtzapffel mentioned a cup filled with hide glue or pitch as a chuck for   
   irregular objects, or actually high precision clock repair because the work   
   can be precisely centered as the melted glue hardens. This describes using   
   modern hot melt glue:   
   http://www.woodturned.co.uk/html/glue_chuck.html   
      
   For the metal sample grinder we placed the sample face down in a ring that   
   we filled with casting resin. The resulting disk fit the grinder holder.   
   jsw   
      
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