When the working part of the machine tool moves, the steel ball circulates in the groove of the support, spreading the wear amount of the support to each steel ball, extending the service life of the linear guide rail. In order to eliminate the gap between bracket and guide, preloading can improve the stability of guide system and obtain preloading. An oversize steel ball is installed between the guide rail and the bracket. The diameter tolerance of steel ball is + / -20 micron. With 0.5micron as increment, the steel ball is screened and classified, and respectively installed on the guide rail. The size of the pre-loaded steel ball depends on the force acting on the steel ball. If the acting force on the steel ball is too large and the preloading time is too long which leads to the increase of the motion resistance of the support, the balance effect problem will appear. In order to improve the sensitivity of the system and reduce the motion resistance, the preloading should be reduced correspondingly. In order to improve the motion accuracy and the retention of precision, sufficient preloading should be required, which are two contradictory aspects.

The working time is too long, so the steel ball begins to wear away. The preloading on the steel ball begins to weaken, resulting in the motion precision of the working parts of the machine tool. If you want to maintain the initial accuracy, you must replace the guide bracket or even replace the guide rail. If the rail system is preloaded and the precision of the system has been lost, the only way is to replace the rolling element.