Novakon 6000 RPM spindle: Run at 9000 ??

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.

its probably a bad idea in the long term. the spindle uses roller bearings, which typically dont like high speed.

if you pulled the lower bearing and replaced it with a decent quality AC bearing, it might hold up much better at that speed.

youll also need to make sure you have a good belt and balanced pulleys or youll find the BELT heating up and failing. the smaller the pulley on the spindle shaft the better.

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Originally Posted by ihavenofish

its probably a bad idea in the long term. the spindle uses roller bearings, which typically dont like high speed.

if you pulled the lower bearing and replaced it with a decent quality AC bearing, it might hold up much better at that speed.

youll also need to make sure you have a good belt and balanced pulleys or youll find the BELT heating up and failing. the smaller the pulley on the spindle shaft the better.

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Aye, I think I'll put the 9K rpm on hold for a bit; I have a spare spindle which I might try to rebuild with better bearings.

Also still struggling with runout - at the tip of the tool it can be up to .001". Which is not good when trying to run a 2-flute at a chipload of .001" per tooth. I'm considering an on-the-mill R8 spindle grinding operation....

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Originally Posted by Frogblender

Aye, I think I'll put the 9K rpm on hold for a bit; I have a spare spindle which I might try to rebuild with better bearings.

Also still struggling with runout - at the tip of the tool it can be up to .001". Which is not good when trying to run a 2-flute at a chipload of .001" per tooth. I'm considering an on-the-mill R8 spindle grinding operation....

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the runout on my nm145 spindle is unmeasurable.

the runout on my COLLETS, well thats a different subject :)

so make sure you figure out what the actual source of runout is or youll be chasing your tail.

cheap r8 collets and ER chucks/collets can be terrible and often have burrs. also any dirt on the collet or taper can throw out a long tool by a large amount.