I've had a long-standing problem with spindle runout on my mini mill, coming in at 0.03 mm. Doesn't sound like much, but causes issues with smaller end mills due to chip load.

I initially thought the spindle might just need a bit more preload on the bearings, but this didn't make any difference.

Since decent bearings are relatively cheap, I decided to replace the stock ones to see if it improves the spindle runout...

My mill is an Amadeal VM32L, but believe this procedure might also apply to:
Warco WM18
Grizzly G0704
Precision Matthews PM-25MV
Weiss VM25L

Update: I purchased a replacement spindle, which has corrected the issue. Runout is now down to less than 10 microns.

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