I may be wrong I don't know if someone has tried this but what about using an old large servo or induction motor frame for a spindle press the inners out and use the frame maby beef up the bearings but the bearings are built for a lot of use as is I would think I have a couple nice 1/6th hp motors I may just have to try this with one. Any Ideas or is this a bad idea?

I've been wondering if the latest RC model motors (spinning at 30.000+) would make a good basis for a spindle? I have an old technigold motor that spins at 33.000 so I may have to try it :)

R/C motor cases for spindles: if you replace the bearings with decent ABEC 7's, they should run pretty true. Unless you're real carefult however, spindle alignment may become an issue.

Some of the cases are pretty flimsy - especially those with cut out cans for mag field tweaking. You might be better off simply machining a case from seamless tubing, especially with regard to stiffness.

what about larger motors like 1/6th hp they wouldn't be flimsy might need better bearings for higher speeds?

Bearing SIZE is the predominant determinator of speed potential - any bearing catalog clearly shows that relationship.

When you start reaching the speed limitor, then internal mods start to gets tweaked to enhance life at the high speed (IE:plastic cages versus riveted cage, special tolerance balls,etc). Special lubes also help. Mounting accuracy helps more that anything else.

Interstingly, "bettter bearings" (as in ABEC 7 vs ABEC 1) do more for running accuracy than they do for high speed operation potential. However, at speeds approaching the bearing size limitation, ANYTHING you do to improve operating accuracy helps the situation. BUT, when it comes to life calcuations, I don't recall ABEC specs being a factor in the life calc process.