Effects of automatic variable preload device on performance of spindle

To increase the machine accuracy by improving the stiffness of bearings, a preload was applied to bearings. A variable preload technology was necessary to perform machining processes in both low and high speed regions. An automatic variable preload device was fabricated using an eccentric mass. By installing the fabricated device on a spindle, the effect of the automatic variable preload device on the performance of the spindle was analyzed. In the results of the vibration measurement of the spindle, the vibration is increased by 20%–37% according to measurement points at the maximum rotation speed of 5 000 r/min. And, in the results of the noise measurement of the spindle, the spindle rotation speed is increased by about 1.9% and 1.5% at the front and side of the spindle, respectively. Based on the results of this analysis, an improved method that reduces such effects on the performance of the spindle is proposed.