07-23-2016, 08:27 PM
How deep is the scratch? I'd blue a good MT and see where things are touching. Abrasives will remove high spots but also some material (maybe very little) at the end of the abrasive where it contacts the bore. If the scratch is deep with a burr on the sides I'd be tempted to use a curved bladed scraper to cut only the high spots or a small wheel on a die grinder to lower the high spots leaving the rest untouched.
I recently had to do this to the tapper on my 3 jaw where it contacts the spindle on my Hardinge. The jaws need ground to remove a bell mouth. I was checking the unworn backs of the jaws with a dial test indicator before grinding and saw they were out. Close inspection showed a small dent on the end of the mount, that deformed the inside surface. Blueing showed that side of the tapper was not contacting. I used a small scrapper to lower that section. When I tried to check it again with the blueing it locked to the spindle, the way it should. Very light pressure showed a nice even coverage hence contact.
Emery paper would have removed material that should have stayed there. You want to only clean up the damage.
I recently had to do this to the tapper on my 3 jaw where it contacts the spindle on my Hardinge. The jaws need ground to remove a bell mouth. I was checking the unworn backs of the jaws with a dial test indicator before grinding and saw they were out. Close inspection showed a small dent on the end of the mount, that deformed the inside surface. Blueing showed that side of the tapper was not contacting. I used a small scrapper to lower that section. When I tried to check it again with the blueing it locked to the spindle, the way it should. Very light pressure showed a nice even coverage hence contact.
Emery paper would have removed material that should have stayed there. You want to only clean up the damage.
Free advice is worth exactly what you payed for it.
Greg
Greg