I messed and messed with my grinder, couldn't make it concentric, usually .003 to 005 thow out of round. Even bought a new pilot that fit much better, but couldn't make it true
Found an old timer that showed me how to float the grinder. He took one of my ports that i had way off, and seconds had it true. Put my dial on it and it was true.
I rarely can get it that true, but most of the time can get it with in 1/2 of a thou to 1. ( .0005-.001)
Before you do any 65 or grater bottom cuts make sure you have a proper bounce spring in it. or you will shatter a lot of stones. the spring under the stone is a simple thing, haven't shatter a stone sense.
