Rotary Bearing Fits and Tolerancing

Rotary bearings are machine elements that support rotating shafts accurately while providing low friction conditions. In order to maintain a stable bearing performance over a prolonged duration, appropriate bearing fit design considerations are required to avoid any negative effects ([Chart 1]) that may arise from bearings‘ rotary operation.

[Chart 1] Common Issues & Solutions

Issue	Side Effect	Proposed Solution
Significant temperature increase due to high speed rotation.	Shaft diameter may expand causing moment loads, resulting in bearing seizure, and uneven wear.	Choose fitting dimensions with the anticipation of shaft expansion.
Thrust and radial direction clearance variations occurring from applied loads.	Degradation of rotational accuracy. Abnormal noises.	Choose fitting dimensions with anticipation of reformed clearances under load.

Design Examples of Rotary Bearing Applications

The example seen in [Fig. 1] is based on “Inner race rotation/Outer race retained”.

[Fig.1] Example - Inner race rotation : Outer race retained (loading in one direction)

Selection of Bearing Fits Based on Shaft Diameter

Transition fit or interference fit is selected to ensure the shaft and the inner ring will always rotate together.

[Chart 2] Selection Example of Fits (Radial Bearings)

Shaft/Bearing Fits	Applicable For:	Fit Standards
Transition Fit	For light or varying loads	h5, js6, k6, etc.
Interference Fit	For general applications	js5, k5, m5, m6, etc.

Selection of Fits For Bearing Holder Bores

Clearance fit should be chosen for ease of assembly while preventing any deformation of bearings‘ outer/inner races. In general, a Clearance fit (H7) is used. In case of light loading applications (H8) can be used, or (G7) when large temperature variations are to be expected.

[Chart 3] Fit Selection Examples For Bores (Radial Bearings)

Bore Fit Selection	Applicable For:	Fitting Standards
Clearance Fit	General rotation applications	H7
Clearance Fit	Light loads	H8 (wider tolerance than H7)
Clearance Fit	Significant temperature increase	G7 (large clearance)