Abstract: In this paper, a rigorous expression for calculating the path interval, which is based on analyzing the enveloping movement of cutters is obtained and is fit for five-axis NC machining of free form surfaces with general torus cutters. The practical algorithm and measures for improving the calculating efficiency are given. The factors that influence the path interval in five-axis surface machining are discussed, and the approaches to optimizing the tool path are also explored.

Key words: surface machining, path interval, enveloping theory, tool path, five-axis