cylindrical thread cutting tool having a chamfered

Claim 1

A THREADING TOOL NAMELY A TAP OR DIE FOR CUTTING CYLINDRICAL V-SHAPED SCREW THREADS COMPRISING IN COMBINATION (A) AN INITIAL CONICAL ROUGH CUTTING SECTION COMPOSED OF A FORWARD AND A REARWARD PORTION; (B) AN INWARDLY THEREOF CONTINUING CYLINDRICAL FINISH CUTTING SECTION; (C) A PLURALITY OF LONGITUDINALLY EXTENDING FLUTES FORMING A PLURALITY OF V-SHAPED TEETH IN SAID TWO SECTIONS THE DISTANCE BETWEEN ANY TWO POINTS OF NEIGHBORING V-SHAPED TEETH, WHEN MEASURED IN AXIAL DIRECTION OF THE TOOL, BEING EQUAL TO THE PITCH OF THE THREAD TO BE CUT; (D) THE TEETH IN THE FORWARD PORTION OF SAID ROUGH CUTTING SECTION BEING OF SUBSTANTIALLY FULL THREAD DEPTH AND THE TEETH IN THE REARWARD PORTION OF SAID ROUGH CUTTING SECTION BEING CHAMFERED ALONG A CONICAL SURFACE TAPERING AWAY FROM SAID CYLINDRICAL FINISH CUTTING SECTION AT A LARGER ANGLE THAN THAT OF THE CONICAL ROUGH CUTTING SECTION, SO THAT THE SAID CHAMFERED TEETH CUT WITH CONTINUOUSLY INCREASING DEPTH INTO THE THREAD PRECUT BY THE FULLY PROFILED TEETH OF THE FORWARD PORTION OF THE ROUGH CUTTING SECTION THEREBY PREPARING AND LESSENING THE LABOR OF THE IMMEDIATELY FOLLOWING FINISH CUTTING SECTION.