In order to enhance the helical-surface of the screw efficiency and the precision in the non-instantaneous center envelope milling,analyzed and compared the commonly used data fitting algorithm,proposed suited the numerical control processing programming the method,Step-Changing Method,it is a common method in NC programming.

With regard to the question how to cut the helical camber of screw-pump and spiral rod drilling tool in the field of petroleum machine and chemical machine, this paper firstly puts forward the cutting method how to apply the milling with non-instantaneous-pole envelope principle with plate milling cutter in our country.

By using the non-instantaneous section envelope machining principle, a mathematical model of mold grinding helical-spur cylinder gear is established,which is a calculating method to shape axile sectional of grinding wheel for numerical control mold grinding helical-spur cylinder gear.