Machine Design

Assembly And Fitting Guidelines For Bearings

The table of recommended fits is based on tolerance levels for bearings of ABEC 5 precision or higher. If the outer or inner ring face is to be clamped or butted against a shoulder, ensure the shoulder configuration provides a good mounting surface. The shoulder face must be perpendicular to the bearing mounting seat. The maximum permissible angle of 14° misalignment is allowed. The shoulder diameter must meet the requirements shown on the table below.

Assembly technique is critical. After the design is finalized and assembly procedures are being formulated, the bearing static capacity, becomes extremely important. It is easy, for instance, to exceed the 3-lb capacity of a small bearing during assembly. After assembly to the shaft, damage can be done either by direct pressure or by moment load while the bearing-and-shaft subassembly is being forced into a tight housing.

Provide adequate fixturing for handling and assembling precision bearings. When inserting the shaft, fixturing must allow transmitting force only to the inner ring. And when assembling into the housing, force is applied only to the outer ring. Furthermore, the fixturing must prevent moment or shock loads, which could be transmitted through the bearing.

This information provided by NMB Bearings, Chatsworth, Calif.

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