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Installation Torque Ranges for Bearing Retaining Nuts?

Installation Torque Ranges for Bearing Retaining Nuts?

(OP)
Guys...

Many tech/design manuals fail to specify toqure-ranges [XXY--YYY inch pounds] for these type large diameter plain nuts, typically used to retain inner bearing races on a shaft [with locking washers or pins].

I have always been advised that "snug" [torque-wrench encounters sharp rise in torque when nut becomes firmly/properly seated]... is far better than over-torqued due to potential for anti-friction bearing binding.

When put into actual values, for-instance, an MS19068-40 or MS172242 nut [1.173-18] nut should be torqued 150--185-inch-# [Torque into this range, wait a few seconds for settling, back-off torque, then immediately final torque to low end-of range... and then advance nut until one or more lock-washer tabs [or pins] engage nut recesses or openings.
A table I developed looks like this [partial list of values]

0.9375-16 135--165-In#
0.9690-32 140--170-In#
1.0000-16 145--175-In#
1.1730-18 150--185-In#
1.2500-16 175--205-In#
1.3125-18 190--240-In#
1.3760-18 200--250-In#
1.4375-16 210--255-In#
1.5000-16 220--265-In#
Etc..

NOTE. One questionable reference I have actually increases these torques by 10X which seems absurd for bearing in mechanical assys.

This method assumes bearing inner-races are installed in the threaded shaft wet with grease; there is a slight grease lube on threads; and there is little/no run-on torque.

Comments? Your experiences?

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

RE: Installation Torque Ranges for Bearing Retaining Nuts?

You have just described a good part of the reason why the auto industry went to unitized front hubs, where the bearing clearance or preload is set at the bearing factory, and everyone else's opinion is removed from the bearing lifecycle cost equation.

Mike Halloran
Pembroke Pines, FL, USA

RE: Installation Torque Ranges for Bearing Retaining Nuts?

I would think the tightening procedure would be strictly a function of the type of bearing and the intent of the designer, not a function of the axle nut. I have had to measure the torque required to turn the bearing assembly to arrive at the proper axle nut preload for tapered roller bearings. In that case the torque on the nut is irrelevant, the axial preload is important. But if the bearings are ball or spherical roller, they usually do not tolerate much axial preload. What do the bearings require? No single procedure will cover all bearings.

Timelord

RE: Installation Torque Ranges for Bearing Retaining Nuts?

(OP)
Timelord...

Good point. The ball bearings in question are typical for aero-mechanical components. Most use lightly packed-grease or oil-bath lubrication, intended for radial restraint and torsional anti-friction. Axial loads are usually very light-to-non-existant by design; and/or have other methods to restrain axial forces. In many cases, weight is a factor: the bearings are often designated as medium, light or extra-light duty.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

RE: Installation Torque Ranges for Bearing Retaining Nuts?

Your first description of the bearing arrangement suggests to me the inner or outer races are clamped directly together or against carefully controlled spacers and the preload is "built in" to the bearings.

For similar arrangements in precision spindles the torque recommended by FAG is on page 56 and 57 here -
http://www.schaeffler.com/remotemedien/media/_shar...
Note the recommendation for initially torquing to 3X to "eliminate or reduce settling effects."

For ruggeder bearings with very heavy axial loads (like for ball screws etc) the nut torque and clamping are on page 58.

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