Toroidal grinding method for curved cutting edge twist drills

In this paper, a new grinding procedure for the curved cutting edge twist drills is presented, i.e., the toroidal grinding procedure. Within this procedure, the clearance surface of the twist drill is a cylindrical helicoid surface with a constant pitch. Based on the principle of distance minimization and envelope theory, a numerical method of calculating the grinding wheel profile is developed. This grinding method allows the profile of the main cutting edge to be continuous and obtained directly during the grinding procedure. The feasibility of the toroidal grinding method is verified by drill grinding experiment and drilling measurements.