Re: Warm left/rear bearing


Thanks once again folks. 

Since I emailed last, I threw the chuck on it and ran it for about 30 minutes (no cutting) at the 740RPM speed. The small bearing hovered right around 90f. The large/front was still lower, but only by a bit (82f). For sure an improvement from the the first test. Id say the ambient temps have been around 65f in the shop today. 

I don’t have the final shim measurements with me. IIRC they were roughly in the .016 area - giving me very near .001 runout on the large  bearing, and a tad under .001 for the small bearing. I will wait to see if I need further changes when I can measure with the tenth indicator. 

I will also keep an eye on the temps over the next couple days and projects. I can see fluctuations in ambient temps requiring changes, or at least it effecting initial bearings temps as the oil reacts to the ambient shop temperature. 

And the most important thing - no binding so far.  Let’s hope it stays that way!

Thanks so much for all your help!!!


On Feb 13, 2021, at 2:56 PM, wlw19958 <wlw-19958@...> wrote:

Hi There,

There are several reasons why a bearing will run warmer than another. 
Not the least of which are the clearances in the bearings.  Unfortunately,
the OP hasn't posted his readings.  I understand that a 1/2 thousandths
indicator isn't the best type to use in this situation but if it is the best one
has at the moment...

To discuss why a bearing may run warmer (clearances aside) can be dirt,
burrs, or anything else that might interfere with alignment and clamping
pressure on the bearing shell.  The slightest nick or ding can be the problem.

I will have to disagree with Steve on bearing break-in.  Even though the spindle
has run-in with the current bearings, if the shim packs have been adjusted,
it will change the shape of the bearing and the points of contact will change
(or more correctly, the highs and lows of the bearing will change).  This will
necessitate a certain amount of run-in to even out (depending on the amount 
of change that has taken place).

In my experience, I have adjusted the spindle bearings and brought them
into spec. and then a month later, found that they needed adjustment again.
So, things do change while the spindle runs and subject to vibration and
hot/cold cycling.

Good Luck!
-Blue Chips-

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