Don't forget drills cut oversize,
Drills are roughing tools most cut at least 0.001″ to 0.005″ oversize holes in real world use. This is can be caused by the drill not being properly sharpened and/or spindle run out. If you want an accurate size drilled hole, use an under-size drill and then use a reamer.
Precisely so, Smolley. I did look into this further and you're quite correct. A 1/4" reamer produces a 1/4" hole, not a 0.25025" one as I'd supposed. Further, for a quarter inch reamer, one needs to produce a hole which is 8 thou undersize to give it the optimum amount of scarring to remove. So it's a case of working backwards to find a suitable drill, allowing for the fact that it will produce a bigger hole than its stated size. To tidy up the other loose ends, 2 thou undersize makes for a good 'interference fit' and 2 thou clearance for a shaft in a bushing makes for happy running.
This sounds like it should be an oilite bearing. Brian
Perfectly sound suggestion, Brian.
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