I have a comment.
I have seen credible comments from guys with experience, that the grease used in milling spindles, had great effect.

Re: heating at higher rpms, power used, etc.
Like 30-50% of the power went to heat, vs 5%, with better grease.
And noise decreased 50% or so, by tfar method.
(That Feels About Right).

Kluber Isoflex 15 is the gold std, for high end machine tool industrial spindles.
It is very expensive.
You need very little, about 1.5 cm3 for a big spindle bearing.

I bought a 50 gm tube, for 1 micron spindles I am making, 4 of, experimental/commercial test samples, with real abec 9/iso 2, bearings in 25 and 40 mm D.
I will make 4 test spindles, 2 of 25 mm and 2 of 40 mm, with both bearings, and see how they work.
Yes, the spindle at 40 mm is now hardened, ground, polished, has 2 microns tir (in spec, just) but I will use a soft lap and diamond paste to reduce the error a bit.

Anyway, better grease has reportedly made a major difference on spindles.
If You want some, I am happy to mail some Kluber "unicorn snot value" grease to You, free.
I doubt the grease has any major effect on accuracy .. but ..

I think it quite probable, perhaps, the grease can/will point out the next error in the chain.
Contact me any way You want, if You want to try some.
One email is greystoneprecision at the google mail dot com.

I do know for a fact, that modern cnc lathes (tools) use P4 bearings or better, since the packaging on mine says so.
And my factory training.
And these bearings do very much benefit from rgw better grease, mostly at higher speeds 2-5k and up.

Personally, I doubt it matters at low speeds, but think I might well be wrong.
CNC machining is often about corner cases, and stuff works different to what one might expect.

The tiny balls in bs supports and nuts actually run really fast at their surface speed.
Anyway, You want a bit, You can have some.
No conditions at all.

Quote Originally Posted by Agathon View Post
Decided to strip the ball-screws and repack with new balls: