![]() ![]() ![]() Japanese Unexamined Patent Application Publication No. There is known a thread forming tap including (i) a complete thread portion and (ii) a leading portion which is provided to be contiguous with the complete thread portion and which has a diameter reduced in a direction toward a distal end, such that the complete thread portion and the leading portion are provided with an external thread in which protruding portions and relieved portions are alternately formed, wherein the leading portion is introduced into a prepared hole formed in a workpiece and then the thread forming tap is screwed into the prepared hole, whereby the protruding portions of the external thread are caused to bite into an inner-wall-surface layer portion of the prepared hole, so as to cause the inner-wall-surface layer portion to be plastically deformed for thereby forming an internal thread (see Patent Documents 1 and 2). The present invention relates to a thread forming tap, and, more particularly, to a technique for reducing a torque in a tapping operation in which an internal thread is machined by the thread forming tap. ![]() The thread forming tap according to claim 1, wherein the sharp crest is provided in the thread ridge exclusively in the leading portion, and wherein a crest of the thread ridge in the complete thread portion has a shape corresponding to a shape of a root of the internal thread. ![]() The thread forming tap according to claim 1, wherein the side surfaces of the sharp crest intersect with each other in a top end portion of the sharp crest, and wherein the top end portion is rounded in the axial cross section.ħ. The thread forming tap according to claim 1, wherein the side surfaces of the sharp crest are connected directly to the flanks, respectively.Ħ. The thread forming tap according to claim 1, wherein the inclination angle of one of the side surfaces of the sharp crest and the inclination angle of the other of the side surfaces of the sharp crest are equal to each other.ĥ. The thread forming tap according to claim 1, wherein the side surfaces of the sharp crest intersect with each other in a top end portion of the sharp crest, and wherein an internal angle of the top end portion is within a range from 80° to 160°.Ĥ. The thread forming tap according to claim 1, wherein the inclination angle of each of the side surfaces of the sharp crest is within a range from 40° to 80°.ģ. A thread forming tap comprising a complete thread portion and a leading portion which is provided to be contiguous with the complete thread portion and which has a diameter reduced in a direction toward a distal end of the thread forming tap, such that the complete thread portion and the leading portion are provided with an external thread in which protruding portions and relieved portions are alternately formed, and such that a thread ridge of the external thread has a cross sectional shape corresponding to a shape of a valley of the internal thread that is to be formed, and extends along a helix having a lead angle of the internal thread, wherein the thread ridge of the external thread has, in an axial cross section that is parallel to an axis of the thread forming tap, a triangular shape as the cross sectional shape that is defined by a pair of flanks located on respective opposite sides in a direction of the axis, such that each of the flanks is inclined by a predetermined flank angle corresponding to a shape of a valley of the internal thread and wherein a sharp crest is provided in a top portion of the thread ridge at least in the leading portion, and has, in the axial cross section, a triangular shape that is defined by a pair of side surfaces located on respective opposite sides in the direction of the axis, such that each of the side surfaces is inclined by an inclination angle that is larger than the flank angle.Ģ. ![]()
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