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# Fitting and clamping bearing rings

Super-precision angular contact ball bearings are typically located axially on shafts or in housings with either precision lock nuts (fig. 1) or end plates. These components require high geometrical precision and good mechanical strength to provide adequate support and location.

The tightening torque Mt, for precision lock nuts or end plate bolts, must be sufficient to keep all components, including the bearings, in place without causing distortions or other damage.

For information about precision lock nuts, refer to Precision lock nuts.

Calculating the required tightening torque
Due to the number of variables (friction between mating components, degree of interference fit, increased preload due to interference fit etc.), it is not possible to accurately calculate the required tightening torque Mt for a precision lock nut or the bolts in an end plate. The following formulae can be used to estimate Mt, but the results should be verified during operation.

The required axial clamping force for a precision lock nut or the bolts in an end plate can be estimated from

The required tightening torque for a precision lock nut can be estimated from

The required tightening torque for end plate bolts can be estimated from

where

 Mt = required tightening torque [Nmm] Pa = required axial clamping force [N] Fc = axial fitting force [N] for bearings in the 718 .. D, 719 .. D, 70 .. D and 72 .. D series (table 1) for bearings in the 719 .. E, 70 .. E and S70 .. W series (table 2) for bearings in the 719 .. B and 70 .. B series (table 3) Fs = minimum axial clamping force [N] for bearings in the 718 .. D, 719 .. D, 70 .. D and 72 .. D series (table 1) for bearings in the 719 .. E, 70 .. E and S70 .. W series (table 2) for bearings in the 719 .. B and 70 .. B series (table 3) GA,B,C,D = pre-set bearing preload, prior to mounting [N] (→ product table) K = calculation factor dependent on the thread (table 4) Ncp = number of bearings in the same orientation as the bearing that the precision lock nut or end plate is in direct contact with1) Nb = number of end plate bolts

1) This is not the total number of bearings in the arrangement, only those that require to be moved to close gaps between rings to achieve pre-set preload. Refer also to Locking procedure.

## Locking procedure

When locating super-precision angular contact ball bearings axially using a precision lock nut or end plate, the following procedure should be applied to be sure that all of the bearings are fully seated and the clamping force is re-set to the estimated required level.
1. Tighten the lock nut / end plate bolts 2 to 3 times tighter than the value for Mt.
2. Loosen the lock nut / end plate bolts.
3. Retighten the lock nut / end plate bolts to the value of Mt.