Nonlinearities in Spindle Bearings and Their Effects

Summary It is shown, both computationally and experimentally, that preloaded roller and ball bearings exhibit characteristics of “softening” sorings with a change of stiffness at a deflection surpassing the preload in a ratio of about 1/0.5. In combination with the flexibility of the spindle itself the softening may then amount, in the various spindle modes, to ratios from 1/0.5 to about 1/0.8. This is also confirmed by comparing Transfer Functions measured on a spindle with roller bearings and another with angular contact ball bearings with simulated responses of models with softening springs. However, it was found that for a better match simultaneously a varying damning coefficient increasing with the displacement must be considered. Finally, stability against chatter was analyzed and it was found that for a higher limit of stability the double stiffness of the preloaded is essential but, beyond the limit the softening spring and increasing damping both contribute to decreasing the magnitude of the vibrations.