Abstract: An optimal method of arc fitting in NC manufacturing is proposed. It adopted the method of optimal biarc fitting and error controlling, in order to improve some existing problems, such as the numbers of fitting data points and arc's segments are too many, the error controlling is difficult in arc fitting and so on. This method has the following adventages: the number of fitting data points is reduced greatly; The computation is simple; The interpolation error is controlled easy. Therefore, it has practical significance in CNC machining of 3-D sculptured surfaces.

Key words: Biarc fitting, Cubic parameter spline, Cubic spline, Inflection point