Threaded training drills

Disclosed is a thread-forming drill, wherein a frictional torque or a heat generation is reduced because the edge portion is substantially zero in connection with a shape near the tip of a projection (δ = 0 °), thereby forming a contact surface with a work piece at the time of thread formation to reduce. In a section for a rough plastic deformation of the of the tip of a projection (δ = 0 °) is separated, the projection has an Archimedes curve shape where the allowance (R) varies linearly, while plastic in a portion for a final deformation near the tip changes the shape of the protrusion according to a quadratic curve. Since a change in the amount of free (R) is reduced near the upper end, where the processing load is large, a thread formation is carried out smoothly and thereby a frictional torque or a heat generation can be reduced without sacrificing the durability of the protrusion. Since a frictional torque or a heat generation is reduced, without sacrificing the durability of the protrusion, because of the reduction of the edge and the particular shape of the projection, the occurrence of welding or wear or damage to the protrusion is minimized, even if a thread cutting is carried out under conditions which are susceptible to welding, for example, a high-speed work, and thus the life of a tool is prolonged.