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Originally Posted by dlavery
For small round holes, multi-drill to 3-5 mils under size, then use a reamer. Do not just use a drill - a standard twist drill will give you a triangular hole (there is a good, concise discussion of this here). For larger holes, cut out the bulk of the material with a hole saw or mill, then finish with a boring head to get a hole that is truly round.
Machinists were making large round holes in workpieces for decades before anyone ever thought about how to control a cutting head with a computer. All you need is the right tooling, the right experience, and the right amount of patience. |
If you plan to press fit a bunch of bearings of the same size (ie... 1/2" ID = 9/8" OD, or 3/8" ID = 7/8" OD) Like we tend to do each year, it might be worth it to invest in an undersized reamers (
from here. Last year we used a boring head to get our bearing holes the right size and it worked pretty well. We had a retired machinist last year helping / teaching us how to do some of the milling. We now have a small benchtop CNC which is so much simpler to make small transmission plates with bearing holes and such. The FP gearbox shown
in this thread, was designed on a Wed. night (gears/bearings ordered that night), wrote the g-code on Thursday (with some help from MasterCam), received our gears/bearings on Fri, and had it finished Friday Night. We could have probably made the gearbox on our Smithy Mill, but we're so inexperienced, we'd probably just make a mistake, expecially since you need two sides to line up pretty darn close. The CNC is nice because once you have it set and indexed, it'll cut it out almost perfectly. Unfortunately our benchtop can only cut 3.25" on its y-axis, but it proved useful and is good for students to learn about.