Most applications involving radial bearings utilize one or more types of ball or roller bearings available in various levels of accuracy known as tolerance classes . To evaluate these tolerances uniformly, we use the ABEC and RBEC rating scales as the industry standard in the United States.
For ball bearings these tolerance classes are ABEC 1, ABEC 3, ABEC 5, ABEC 7 and ABEC 9. Similarly, the accuracy levels for roller bearings (cylindrical and spherical) are RBEC 1, RBEC 3, RBEC 5 , RBEC 7 and RBEC 9. For tapered roller bearings a different rating scale is used.
The ABEC and RBEC classes have identical values: for both, the higher the class number, the tighter the bearing tolerances, therefore, the better the bearing's precision, efficiency and speed capabilities.
ABEC (or RBEC) ratings specify size and shape tolerances for individual inner and outer rings. Dimensional tolerances refer to the basic limiting dimensions: the inner diameter of the inner ring, the outer diameter of the outer ring, and the ring widths. Shape tolerances include roundness, taper, eccentricity and parallelism.
Determining the appropriate tolerance class for bearings in a specific application is very important. We encourage designers to adhere to the following general guidelines:
- Designers should always perform a study on the accumulation of maximum and minimum material condition tolerances when sizing components, especially when designing miniature ball bearings.
- Consider different precision level options in terms of direct correlation to bearing performance and life . For example, race parallelism can affect bearing torque, so a non-parallel race condition will cause torque spikes during rotation. In high speed applications, excessive bearing eccentricity can cause an imbalance in the rotating mass. Both conditions can lead to unpredictable bearing life and premature failure.
- Keep in mind that the higher the level of precision, the higher the cost of the bearing.
- Remember that bearings with higher tolerance classes are intended for use in precision applications that require high operating precision, high speed rotation and/or low torque. Common examples include aircraft instruments, machine tool spindles, and dental equipment.
- On the other hand, bearings with lower tolerance classes are acceptable for use in a wide range of applications such as automotive, electric motors and most industrial machines.
