I do alot of cutting in 6061 with .125" endmills, so I desire more RPMs to speed things up. The 6000 rpm motor drives the spindle via 1:1 pulleys. It is trivial to replace one of the pulleys to get a 1.5:1 - which'll drive the spindle at 9000 RPM, instead of the usual 6k. So trivial, in fact, I've done it already. I ran it at 9k for about 2 minutes, but the lower bearing seemed to be heating up at too-fast a rate, so I called it quits on the test until I install another USB temperature monitor on the bottom of the spindle. The top remained cool.

I've recently snugged up the spindle preload and got the runout down to an OK-but-not-great .0004" or so.


Anyone have any insight on running a 6k spindle at 9k?? Is it going to fling away the grease? I can understand cooking the bearings through overtemperature, but I can keep an eye on that with the USB thermometers. Any help appreciated.