SCREW TAP Russian patent published in 2002 - IPC

FIELD: metal working, namely threading by cutting processes, mainly of nut type parts. SUBSTANCE: tap includes starting and sizing portions, reverse conicity of thread, straight chipping grooves, teeth with profile relieved until pointed state, vanes with front tapered portions. In order to enhance accuracy of thread cutting due to lowering profile of thread indentations in opening depending upon reverse conicity value of thread, tapered portions on front surfaces of vanes in starting portion are inclined by angle determined according to given expressions in dependence upon: reverse conicity value along the whole length of tap thread until formation of tapered portions; predetermined lowered value of reverse conicity of thread in starting portion along cutting sides of teeth; width of vanes; teeth relieving value equal to half of decreased mean diameter of thread along width of vane; thread pitch and factor taking into account change of starting portion length corresponding to quantity of thread pitches. EFFECT: enhanced accuracy of thread cutting. 4 dwg, 1 tbl