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.
| 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 Example of Rotary Bearing Applications
The example seen in [Fig. 1] is based on “Inner race rotation/outer race retained”.
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.
| Shaft/Bearing Fits | Applicable For | Fit Standards |
|---|---|---|
| Transition Fit | For light or varying loads | h5 js6 k6 |
| Interference Fit | For general applications | js5 k5 m5 m6 |
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.
| 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) |
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