Select a point m on the cutting edge of helical gear turning tool, and establish the reference plane of tool angle, as shown in the figure. Assuming that the cutting speed at the cutting edge point m is , the base surface is perpendicular to the cutting speed , the cutting plane is composed of the cutting speed and the cutting vector at m, and the main section is perpendicular to the base surface and the cutting plane at the same time.
Define the cutting rake angle and cutting rake angle of the tool in the main section . The included angle between the intersection of the main section and the base surface and the intersection of the main section and the rake surface is the cutting rake angle 0. The included angle between the intersection of the main section and the cutting plane and the intersection of the main section and the flank is the cutting flank angle 0.
According to the definition of cutting angle, the pre cutting angle 0 and post cutting angle 0 can be expressed as:
Of which:
