Machining, Measurement, and Control Laboratory

A Study on Improvement of Contouring Accuracy in Small Circular Motion for NC Machine Tools
Yasuhiko Suzuki, Atsushi Matsubara, Yoshiaki Kakino

This paper deals with controlling feed rate for small circular motion on NC machine tools. Recently new machining methods using small circular interpolation with endmills or direct taps have been used for machining cylindrical holes or tapping. Accordingly, contouring accuracy is getting more important in the new method. Decision of feed rate that influences contouring accuracy is the most important and difficult. So far the maximum feed rate for circular motion is decided according to the normal acceleration constant rule. This rule is a good way to restrict errors due to difference of stiffness between two axes because the errors are mainly proportional to normal acceleration. In the case of small circles, the rule is of no service. That is why errors are increasing as angle speed increases even if normal acceleration is constant. Therefore, the new rule to decide feed rate for small circular motion is needed. This paper analyses what is related with the errors in case of small radii and proposes a new rule to decide feed rate for small circular motion.