Abstract: The theoretical error in five-axis NC machining, which is resulted from approximating the perfect continuous tool path with discrete linear segments, is strictly analyzed. An expression used to estimate the theoretical error and suitable for various types of cutters are given. The error estimate is accurately obtained from the three-dimensional enveloping movement of cutters. The infouences of the local geometry of part surface, the shape and dimensions of cutters, the control parameters of cutter axis, the feed direction, the structure parameters of swing mechanism and the step length have been considered in the obtained expression. Then, the measures to decrease machining error are analyzed, and the algorithm for determining rational step lengths based on assigned accuracy is derived. As a result the machining error can be controlled effectively and the quality of tool path can be improved.

Key words: Error Step length, Five-axis, Numerical control, Surface machining, Tool path