Bearing Design

Shaft and Housing Design

Optimizing ball bearing performance requires careful design in terms of the precision and dimensions of the shaft and housing. When bearings are installed in your application, they will come into contact with the shaft and housing, so this aspect of bearing design is critical.

Bearing Design and Fit

To get optimal performance from your bearing, you must pay special attention to design as regards the fit between the inner ring, outer ring, and the housing. This fit and design must be suitable for the specific equipment involved in your application. For example, too loose a fit could result in a corroded or scored bearing bore and shaft; while too tight a fit could result in unnecessarily large mounting and dismounting forces and too great a reduction in internal bearing clearance.

All rolling bearing manufacturers make bearings to standardized tolerances set forth by the Anti Friction Bearing Manufacturers Association (AFBMA) and the International Standards Organization (ISO). The proper fits can only be obtained by selecting the proper tolerances for the shaft. Each tolerance is designated by a letter and a numeral. The small letter is for shaft fits and the capital letter is for housing bores, and together they locate the tolerance zone in relation to the nominal dimensions. The numeral designation gives the magnitude of the tolerance zone.

Shaft and Housing

Finish precision of bearing shaft and housing

After bearing installation, degradation will occur in the roundness of the bearings if the design and fit of the shaft and housing are not appropriate. The precision and surface roughness of the shaft and housing must be at satisfactory levels to protect the bearings and optimize their performance.

Fillet radii of corners of shaft and housing

The design of the side faces of bearing shafts and housings, or the area contact the bearing side face, causes them to come to the shaft center and fit surface at right angles. The fillet radii of the shaft and housing corners have a maximum permissible radius (ras max) is smaller than minimum permissible chamfer dimensions of the bearings.

Height of shoulder

The design of the shaft and housing shoulders must include a height that is taller than minimum permissible chamfer dimensions. The shoulders also must be designed to contact the side faces of the inner and outer rings.

To design shoulders properly, ensure that the minimum height of shoulders is four times taller than minimum permissible chamfer dimensions. The table and figure on this page provide additional insight into the dimension specifics of this bearing design requirement.