Bearing Tolerances

Bearing Tolerances A bearings accuracy is split between three different aspects, the external dimensional accuracy, the running accuracy and the machining accuracy Accuracy of External Bearing Dimensions This measures the accuracy of the external dimensions of the bearing such as the bore, outer diameter, inner ring width and outer ring width. The difference between the actual measurement and the expected measurement is referred to as the dimensional deviation. The accuracy of the dimensions is important for determining shaft and housing fits. Machining Accuracy The machining accuracy measures the variation of the dimensions when measured on a single bearing and then compared to one another. The variation is then the difference between the largest and smallest measurement on the bearing while the mean variation is taken as the average dimensional difference of the measurements taken. This is important for determining the precision of the manufacturing process and is important when considering tolerances for shafts and housings Running Accuracy Running accuracy is generally referred to as the runout and is a measure of the degree of eccentricity (for radial runout) and “squareness” (for bore and outer diameter) of the bearing. The measurements most often used are that of the inner and outer ring radial runout, a bearing with a high degree of radial runout will produce a greater vibration than a bearing with a low degree of radial runout, this becomes more noticeable at higher speeds. Below is a table of the international standards for bearing accuracy Standard Tolerance Class Bearing Type JIS B 1514 Class 0 class 6x Class 6 Class 5 Class 4 Class 2 All Types ISO 492 Normal class 6 Class 6 Class 5 Class 4 Class 2 Radial Bearings ISO 199 Normal class Class 6 Class 5 Class 4 - Thrust Ball Bearings ISO 578 Class 4 - Class 3 Class 0 Class 0 Tapered Roller Bearings (Inch Type) DIN 620 P0 P6 P5 - P4 P2 All Types ANSI/AFBMA Std. 20 ABEC-1 RBEC-1 ABEC-3 RBEC-3 ABEC-5 RBEC5 ABEC-7 ABEC-9 Radial Bearings excl Tapered