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Bearing Design Factors, Part 2 - Bearing Mounting and Fitting: Radial Play and Interference Fits || Dynaroll

TECHNICAL PAPERS

TECHNICAL PAPERS

DESIGN FACTORS WHEN USING SMALL BEARINGS, PART 2: MOUNTING AND FITTING



Part 2: Mounting and Fitting

By Simon Harrison, Ph.D.
Miniature bearings are generally used in applications where rotational performance (i.e. predictable low torque, runout, stiffness, etc.) is the primary design goal, rather than load/lifetime issues. A previous paper has discussed how the internal geometry of the bearing itself influences the rotational performance of a bearing assembly. This paper addresses the importance of proper handling and assembly methods in the application of miniature bearings.

Radial Play and Interference Fits

The cross-section of the inner and outer races of miniature bearings (sometimes called the turning rings) can be very thin. For bearings of 1/4-inch OD or smaller, the thickness of the race under the ball groove can be less than 0.008 inches. This means that even though the bearing material may be relatively hard steel (Rc 60+), the races are extremely fragile and can be significantly damaged or distorted by the slightest force during the mounting and assembly process.

For such thin section bearings it is also extremely important to note that up to 80% of the interference with mating components will translate into loss of radial play. Since a standard miniature bearing has a radial play between 0.0002 and 0.0004 inches, this means that total interference of 0.0003” can be expected to close up some bearings to the point that they will no longer rotate.


Bearing Mounting and Fitting, Page 2: Radial Play and Interference Fits link