Originally Posted by
awerby
My fellow "engineers" here seem to have different ideas of what "exactly" and "perfect" really mean. The various classifications of fit are something that machinists obsess about, as I tried to indicate with the link I posted. Doubtless with some trial and error one can come up with a hole that will adequately contain a metal rod for most purposes (with maybe a little sandpaper and glue to help). But producing a hole that is really a specified press or sliding fit to a cylinder is more complicated than printing, or even drilling will accomplish. Drilled holes tend to be slightly triangular; they aren't truly round or dimensionally correct. The common practice in machining when accurate holes are called for is to drill undersized, and ream to the correct size.