SCREW TAP Russian patent published in 2002 - IPC

FIELD: metal working, mainly thread cutting by means of nut taps. SUBSTANCE: tap includes starting and sizing portions, inverse conicity along thread and teeth with lowered profile angle. In order to enhance accuracy due to elimination or significant reduction of profile angles of threaded openings, halves of profile angles of teeth of starting portion are decreased in comparison with those of teeth on sizing portion by value determined according to given relation. Mean diameter of thread on teeth of starting portion is lowered by value also determined according to given relation. EFFECT: improved accuracy of thread. 3 dwg, 1 tbl