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Design considerations

Recommended shaft and housing fits

Shaft and housing seats for super-precision axial-radial cylindrical roller bearings should be manufactured to the following tolerance classes:

Accuracy of seats and abutments

If a super-precision axial-radial cylindrical roller bearing is to obtain a high degree of running accuracy and low operating temperature, its associated components must be manufactured to similar levels of precision.

Recommendations for the geometrical tolerances and surface roughness are provided in:

The recommended shaft and housing diameter tolerances, relative to the bearing bore and outside diameter tolerances result in a transition fit, tending towards clearance. In some cases, however, an interference fit may result for either the bearing inner or outer ring. When this occurs, preload on the radial roller set will increase, as will contact stresses, friction and frictional heat.
To optimize operating conditions and running accuracy in applications where there is inner ring rotation, the fit between the shaft and inner ring should be a loose fit that is as close to zero as possible. A near-zero loose fit should be applied to the outer ring and housing when the outer ring rotates.
To help obtain a near-zero loose fit on a shaft, SKF supplies axial-radial cylindrical roller bearings with an inspection report. The report includes the measured deviation from nominal of the inner ring bore diameter. It also includes the measured deviation from nominal of the bearing height and measured running accuracy.

Attachment bolt holes

Axial-radial cylindrical roller bearings require threaded holes for attachment bolts in the shaft and housing. Details about spacing and thread sizes are listed in the product table. At the position of retaining bolts and removal threads, no attachment bolt holes are required.
Bearing NRT 80 A should be fixed with 12 attachment bolts each in the inner and outer ring. For this bearing, the retaining bolts and removal threads are positioned between the attachment bolt holes, evenly spaced at 120°.
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