A Method for Generating Helical Surface of the VPA Hob on a CNC Worm Grinding Machine

Variable pressure angle (VPA) hob is an important cutting tool for generating the twist-free tooth flanks on a crowned involute helical gear used in the high precision gear boxes. However, an appropriate method for generating the VPA hob surface has not proposed yet. Therefore, this paper presents a worm grinding method for generating the helical surface of VPA hob on a CNC worm grinding machine. A mathematical model of the proposed method is established based on a standard hob by controlling rotational motion of the hob axis in the worm grinding process. A numerical example is implemented to verify the merits of the proposed method