Setting and testing preload on milling spindle tapered roller bearing

For a while now I have been rebuilding and repairing this toolroom style milling machine. It is a Chinese model X8130 - basically a Chinese blend of a Deckel FP2, Schaublin 13 and Thiel 159. This one was sold in Australia under the Servian Sermac brand however they were sold under brand names Knuth, Wolf, Comet and various others around the world.

I have just replaced the tapered roller bearing on the NT40 horizontal Spindle. The bearing is a standard size 32211A, i used a P5 grade from ********* Germany. As you can see, bearing preload is set by the two lock nuts that tighten up behind the spacers, thrust bearing and tapered roller bearing.
I have drawings but no torque settings so really don’t know where to start with setting the preload. I have the spindle installed, and by leaving the overarm and vertical head removed, I can test run the horizontal and adjust it with the spindle in place.

How can I test the bearing preload and what results should I be looking for? I have done a bit of searching and googling for info however most I could find were talking about grinding and adjusting shims or spacers for adjustment. I was considering using a dial against a horizontal arbor to test for movement?

Any help or advice would be much appreciated. Here’s a few pics of the machine and spindle assembly for reference.

Any help or advice

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Likely not much help - very old, not the same make - but does have tapered roller bearings

See page 21 and 22

Their instructions generally go along with what I have heard for many years - tapered rollers ARE NOT run with preload - but then what do I know - I am old like these instructions

http://vintagemachinery.org/pubs/2097/19898.pdf

There needs to be some preload to insure that the spindle load is equally shared by all the rollers in the bearing. The bearing assembly stiffness is also determined by the bearing preload. A higher preload will produce a higher bearing stiffness. The preload should be selected so that the radial stiffness of the bearing is about the same as the radial stiffness of the spindle by itself when treated as a flexible cantilevered beam on a rigid support.. The goal is to maximize the radial stiffness of the combined flexible spindle mounted on flexible bearings. The goal is limited by the need for a realistic bearing fatigue life and a acceptable bearing operating temperature.

The Timken catalog does provide some guidance on what to do but it does not make any recommendations. The bearing stiffness change is nonlinear with preload. Small preloads produce large changes in stiffness. As the preload is increased beyond some point it no longer has much effect on the bearing stiffness. A axial preload of 100 pounds may be sufficient for your spindle. The catalog provides a formula for the bearing turning torque once the axial preload has been selected. The preload can be set with a spring scale and a length of string wrapped around the spindle OD once this torque is known.

https://www.timken.com/wp-content/uploads/2016/12/5918_Machine-Tool-Catalog.pdf See page 62.

The heat generated by the bearing will be determined by the spindle speed and the bearing preload. There is also a formula for this in the catalog. If the temperature is too high during continuous spindle operation, for example 160 deg F, then you need to either reduce the preload or restrict the spindle speed. The heat should be limited to about 100 watts for a spindle housing without liquid cooling. This works out to be 2.4 in-lb of torque at 4000 rpm.

The preload may change with increasing spindle and housing temperature.

The simple approach is to turn the spindle by hand while tightening the lock nut. When you detect a slight increase in resistance to motion the preload is about right.

The roller bearing should be seated into the bore by applying a high initial preload and turning the spindle a few times by hand. Then the retaining nut is backed off and the preload set to the running value.

My understanding is that temperature rise is the way to go. Snug up the spindle and run it at top speed
for bit. If it stays cool, bump up the preload a bit, and try again. When it becomes warm to the touch
after steady running that's about right.

Hot is right out....

johnoder said:

Likely not much help - very old, not the same make - but does have tapered roller bearings

See page 21 and 22

Their instructions generally go along with what I have heard for many years - tapered rollers ARE NOT run with preload - but then what do I know - I am old like these instructions

http://vintagemachinery.org/pubs/2097/19898.pdf

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Only one example admittedly John but the " Timken " bearings on the facing slide of the " Kearns- Richards " Hor bores were quite heavily pre loaded. I forget the numbers now unfortunately.

Regards Tyrone.

What struck me in the Cincinnati instructions was that even with .0005" end play (obviously no preload) the spindle STILL gets quite warm at speed - not something you would want to leave your hand on for very long

Temperature rise and Max Temp are how the headstock bearings on the Weiler lathe are set.

CalG said:

Temperature rise and Max Temp are how the headstock bearings on the Weiler lathe are set.

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Hi
I did a lot of research on this when I had to set preload on my lathe spindle. I ended up with the same method.

Dazz