This is hardly related to firearms and will mean something only to hobby machinists, but I believe this is still the best place to discuss it. I'm in the middle of restoring a Myford dividing head. I might publish something about that because it should be of interest to other hobby machinists. But for now I'll limit this to my work on the over-arm which is nothing more than a one inch dia x 12 inch long bar (25.40 x 305mm). One end of this bar is supposed to slide in the bore of the body casting where it can be locked with two pinch screws. The other end carries a small cast bracket which carries a dead centre. I've had this tool lying around for years. I bought it cheap because it had parts missing which I figured I could make. The over-arm wouldn't enter it's matching hole under any circumstances and I therefore suspect that it had never done so until I worked on it. How it left the factory in that condition is another question. It was exactly 25.40mm everywhere, no variance. As there are no centre holes it would have been impossible to machine it, not to mention that turning off such a tiny amount would have risked ending up too small. So I took the long route and took it down with wet or dry. My method was to rub it lengthwise with 220 grit on a rubber sanding pad at all points of the clock which amounted to about 20 facets. But to keep it round and avoid creating facets I rocked the pad sideways for overlapping strokes. I first coated it with marking blue to see where I'd sanded and where I hadn't. After each such sanding I mounted it vertically in the vise and sanded it shoe-shine fashion. It took four such treatments to get to the point where it was close to entering the hole but not quite. Micrometer measurements at several places were 25.38mm except for two 25.385 high spots which were inconsequential. Yesterday I gave it two more treatments and it now slides in the bore but a bit more stiffly than I'd like, so on Monday a bit more work should get it perfect. My second attempt was a bit less accurate - varied 25.36 - 25.37 with two 25.375 high spots but that's inconsequential - .01mm = 0.05 all round which is a miniscule two tenths in old money.