Quote:
Originally Posted by InFlight
An experienced mentor machinist with a Starrett micrometer can achieve half a thousand on a nice big lathe that well is adjusted.
An above average student machinist on a mini-lathe using $15 digital calipers would be good to hold 0.002".
My point was either end of the machinist spectrum could take a 1.125 mill or drill and undersized it enough to achieve a snug R8 bearing fit.
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I can get to half a thousandth without too much care on the small Taig that the woodshop teacher owns. If one is using a good pair of Brown and Sharpe calipers or Mitutoyo, those hold to 0.0005" easily. Of course, maintaining a "good pair" of quality calipers is difficult in a student's hands.
Ironically, I find that using a telescoping gauge and micrometer is harder for me than just trusting the calipers, although either method isn't impossible.
Back when we used to use the boring head, all measurements would be taken on the B&S calipers, well before I was on the team. They were able to get reasonably good presses on bearings, although I don't know what the skill level of the people were before I was there.
That being said if I tried to get that tolerance on steel, I wouldn't have much luck.
Drilling a 1.125" hole with a drill bit I would try to avoid. Using an endmill will get those tolerances but a drill bit won't hold the tolerances easily unless you drill undersized by 1/64" or something first, and even then I'm not sure. The largest hole I have drilled in metal was with a 7/8" drill bit, and that did not go as well as just using an endmill of the same size. What is your method to make sure it works correctly?