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Accuracy of seats and abutments

Geometrical and running accuracy

Maximum running accuracy, high speeds and low operating temperatures can only be achieved, even with super-precision bearings, if the mating parts and other associated components are made with equal precision as the bearings. Deviations from geometric form of associated seats and abutments should therefore be kept to a minimum when machining mating parts. Form and position recommendations in accordance with ISO 1101:2012 are provided in table 1.
Thin-walled bearing rings adapt themselves to the form of their seat. Any errors of form on the shaft or housing seat can therefore affect the bearing raceways and bearing performance, e.g. angular misalignment of one bearing ring relative to the other, can cause loss of running accuracy, load concentration and high operating temperatures, particularly at high speeds. The numerical values of IT tolerance grades in accordance with ISO 286-1:2010 are listed in table 2.

Surface roughness

The surface roughness of a bearing seat does not have the same degree of influence on bearing performance as the dimensional and geometrical tolerances of the seat. However, obtaining a desired interference fit depends on the roughness of the mating surfaces, which is directly proportional to fit accuracy. Guideline values for the mean surface roughness Ra are listed in table 3 for different bearing tolerance classes. These recommendations apply to ground seats.
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