Abstract: The once generating cut of thread is accomplished owing to the application of hard cutting technology to thread whirling process. The undercutting trouble in internal whirling process of external thread is mathematically analyzed with coordinate transformation in order to acquire the machining mechanism . The transforming relationship between tool profile and thread raceway profile is found. The effect on thread raceway undercutting induced by tool profile, tool rake angle, rotating diameter of tool tip and speed ratio of workpiece-tool, is discussed via programming in commercial software Matlab. It is found that undercutting is inevitable in internal whirling process using tool designed directly by thread raceway profile, and it can’t be eliminated using tool designed with means of contact condition. A design method of tool profile for internal whirling is proposed to avoid undercutting. The criteria and steps for above parameters’ determining in internal whirling process are concluded based on requirements of profiling accuracy and roughness. Case of a specified double arc raceway of lead-screw is studied in the discussion.

Key words: Rotating diameter of tool tip, Speed ratio, Thread whirling, Tool profile, Undercutting