Average roughness height of the shaft

When the average roughness height R_z of the shaft is specified, the influence of the interference loss due to smoothing of the roughness peaks on the shaft is taken into consideration.

The higher the surface roughness of the mating parts, the greater the smoothing effect which results in an interference loss.  The smoothing effect of the bearings can be neglected since the bearing rings are hardened and precision ground and has finer surfaces compared to shaft or casing. Thus, 

Effective interference = Interference of mating parts - g_F * R_z 

Note: The default smoothing factor value of g_F = 0.8 is taken from Wälzlagerpraxis. In the old calculation kernel from FVA 364 the smoothing factor value was g_F=1,4