Development of precise cylindrical grinding by ball centers: effect of ball wear

Abstract

In high-precision cylindrical grinding and precision measurement, it is known that accurate and inexpensive steel balls used in place of cone centers enable one to grind and to measure the workpiece accurately without the influence of the misalignments and geometrical deviations of the center holes. The purpose of this study is to explain the supporting characteristics of these ball centers. In this article, endurance tests were performed and ball wear was measured to investigate the effect of the wear on the rotational accuracy and the roundness of the workpiece. The main results obtained are as follows. (1) The rotational accuracy and the roundness of the workpiece remained at high levels during the endurance test of 3 hours regardless of the ball wear. Consequently, the wear had little effect on the accuracy. (2) The contact points between the ball and the holder gradually shifted to other points that were not yet worn. This averaging effect maintains the rotational accuracy at a high level. (3) Lubricating the supports every quarter hour reduced the ball wear to half. Moreover, the lubrication was effective in preventing the ball from exfoliating. Therefore, there is no need to be concerned about ball wear in ordinary circumstances.