| 摘要 |
The cold forming tap according to the present embodiment is constructed such that ones of protruding portions which are located adjacent to each other in the axial direction are removed down to a root of a thread of the cold forming tap, and a portion corresponding to the root of each of the removed protruding portions is provided with the cutting edge having a diameter equal to a minor diameter of an internal thread to be formed by the cold forming tap. This construction permits a maximum diameter position of the root not to be located at relief portions which are adjacent to the protruding portions of the external thread portion, whereby a concave-convex shape defined by the crest and a concave-convex shape defined by the root coincide with each other as viewed in the circumferential direction. This coincidence between the respective concave-convex shapes makes it possible to form simultaneously the ridge and root of the external thread portion with high accuracy and efficiency, by employing a grinding wheel having a thread profile formed on its outer circumferential surface in a step referred to as a thread grinding, considerably facilitating a dimension control of the thread of the external thread portion, and leading to a reduced cost for the production. <IMAGE> |
