As an ideal condition, the initial clearance in rolling bearings gi should be so determined that the radial clearance might be close to zero in operating condition. gp is the reduction in the bearing clearance caused by elastic expansion of the inner ring at the time that the ring is mounted with a press fit. gl is the increase in clearance under axial load applied to the bearing, and gt is the reduction in clearance by thermal expansion. Then the value of gi may be expressed as follows:
gi = gp + gt -gl
Particularly in the ball bearing, the values of gi for all cases cover the wide range, because the operating and using conditions vary widely and fit tolerance is wide too. So we studied, in the case that the distribution curves of dimension differences between the shaft and bore diameters are shown as a Gauss-curve, to obtain the suitable range of gi by reducing the fit tolerance, while keeping still a high dcgree of probability of fit.
According to this point of view, we calculated, as an example, the values of gi of the bearing No. 6312 (Single row deep groove ball bearing, bore diameter 60 mm) under various fit tolerances and operating conditions.