New calculating method of nodes based on arc approaching lnvolute with equal errors;

Secondly, analysed the approach model, described circular arc approximation method, approaching blade curved surface with this method and realized raise of the approach speed.

This paper presents a novel method of arc approximation for shape matching-Max Ratio.

Aim at NC machine tool can not machining the noncircular curve and listing function with direct interpolation,a method of thrice shape function interpolation and double circular arc approximation are suggested to machining the contour line, and the flowchart realized it in computer was given.