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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My students could hit 0.001" easy with any lathe we have(maybe not the Grizzly) my experienced lathe students could hit that +- 0.0005" most of the time with a few pointers. But really reamers are the way to make it easy, you can make your own for cleaning up holes if you have patience, spare time, and some tool steel.
My favorite "bugdet" calipers by the way are a $35 pair of Fowler digital calipers from
Amazon
Quote:
Originally Posted by s_forbes
I don't think that this is what you're looking for, but we used this step drill bit to clean up bearing holes in our waterjetted pieces this past season. It can put a 7/8" OD hole into 1/8" thick material, or run through thicker material with a 1.125" OD hole. Just the right size for the 3/8" and 1/2" bearings we all use.
http://www.mcmaster.com/#8841a35
Step drills are cheaper than reamers, but they can wander if you are taking off a lot of material. Our gearboxes worked great, but we had padded in an extra .003" between adjacent bearing holes to prevent gears from binding if things were off. If you want tighter tolerances, you probably don't want a step drill. |
I will second the step drill method! It's super fast and easy and in my opinion is SO worth the $45 or so it costs. It will post size your holes and will be solid as long as you use positive retention like rivets or retaining compound.
My personal favorite method for making a 1.125 hole in aluminum has to be a Carpenter's Spade Drill. I am dead serious here. It probably won't be fantastic for gearbox plates but with a little time on the grinder to modify the bit it will make a press fit hole every time. The only major limits on this method is it can't go through much more than 0.125 thick material and nothing tougher than aluminum. You should never try and do this by hand, not really for danger reasons, it just won't work. Your puny meat fingers aren't as stiff as a drill press. Below is roughly what a modified spade bit looks like.
If you don't believe me watch AnthonyDV drill a hole and hand press a bearing in.
https://youtu.be/yIonCvyEFks?t=29m40s