Circular tests for accurate performance evaluation of machine tools via an analysis of eccentricity

Circular tests to determine the circular/spherical deviation of machine tools based on double ball-bar measurements are proposed and applied to machine tools for accurate performance evaluation. In current circular tests, eccentricity is mathematically removed from the measured data to evaluate performance. However, eccentricity is affected not only by set-up error of the double ball-bar, which is trivial, but also by geometric error, which this test is intended to determine. The relationship between eccentricity and geometric error was investigated during circular deviation measurements using a simple example. The results demonstrated that the measured data must be evaluated as they are, without any mathematical modifications. Additionally, the circular test must be performed while ensuring negligible set-up error. The proposed approach was applied to three machine tools to investigate the effect of eccentricity when circular/spherical deviation appears.