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Tolerances for bearing seats and abutments

Performance and operating conditionsBearing type and arrangementBearing sizeLubricationOperating temperature and speedBearing interfacesBearing executionSealing, mounting and dismounting

Dimensional tolerances for bearing seats are dictated by the required fit. Precision requirements of the application will direct you to which bearing tolerance class to use (→ Bearing execution), and consequently, what run-out tolerance of the seat is needed. The run-out of the seat is specified by the total radial run-out of the seat surface and the total axial run-out of the abutment (ISO 1101, 18.16).
For bearings with Normal tolerances in general industrial applications, seats are typically machined to the following tolerances:
  • shaft seats to grade IT6 dimensional tolerances and grade IT5 total run-out tolerances
  • housing seats to grade IT7 dimensional tolerances and grade IT6 total run-out tolerances
Suitable combinations of tolerance grades are listed in table 1. The tolerance zone for the total radial run-out is limited to half of the ISO tolerance grade, because the run-out tolerance is specified as a difference in radii of two coaxial cylinders, and the ISO tolerance grade refers to the diameter.

For seats of bearings mounted on withdrawal or adapter sleeves, wider diameter tolerances are permissible. The total run-out tolerances should be the same as for bearings on cylindrical seats.

Tolerance values for ISO tolerance grades are listed in table 2.

Example

A deep groove ball bearing 6030 is to be used in an electric motor. The bearing accommodates normal to heavy loads (0,05 C < P ≤ 0,1 C), and requirements for speed and precision are moderate. An interference fit on the shaft is required. For this fit, the shaft diameter should be 150 m6Ⓔ. The total radial run-out should be within IT5/2 (from table 2: 18/2 = 9 µm), and the total axial run-out of the abutment should be within IT5 (from table 2: 18 µm).

Fig. 1 shows the dimensional tolerance zone in grey and the tolerance zone for the total radial run-out in blue. The blue zone can be located at any place within the grey zone, but must not be wider than 9 µm.

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