I am little late to the party. Two babies and the new job are demanding. Wish I
had more time for coins. I am actually laying in bed and should be sleeping. Anyways...
I use diamond bits in a pin vise. These can be gotten from dentist catalogs and should hold up pretty well. I refused to pay for some and my dentist friend hooked me up. Then another friend here helped me out as well. What is nice abou the bits is that they seem cheaper in
price and have a wide variety of sizes. My dental grade ones
work well. Just remember, the finer the grit the more often you need to clean out because they clog.
These will get burnished themselves though. It is a fact of them. Just like sandpaper on
wood they wear out. Sandpaper doesn't last very long either. Also, the intention of these
tools were for use on teeth not metal coins.
Let us know how the HF ones do.