TAP TERMINOLOGY C f Internal centre the countersink in one or both ends of the tap. P Pitch the distance, measured parallel to the tap axis, between two corresponding and successive points on the thread profile. α Angle of thread the angle between the flanks of the thread (measured in an axial plane). δ Thread lead angle the angle made by the spiral of the thread and a plane perpendicular to the tap axis, measured on the pitch diameter line. β Chamfer angle the angle between the chamfer and the tap axis, measured in an axial plane. γ Rake angle the angle between the cutting face of the tap and a radial line passing through the crest of the tooth at the cutting edge.
L Square length the length of the flats that form the square. L 1 Total length the complete length of the tap from end to end, excluding external centres. L 2 Thread length the length of the threaded section of the tap. L 3 Usable length the length measured from the front end of the tap to the end of the neck section. This length determines the maximum threadable depth on taps with reinforced shank. L 4 Chamfer length the length of the chamfer measured parallel to the tap axis, excluding the chamfer bevel. L 5 Flute length the axial length of the flute including the cutter sweep. C m External centre the pointed end of the tap.
T Land width the chordal width of material between two successive flutes. S Flute the longitudinal channels in a tap which create cutting edges. The flutes provide space for chips and passage for coolant/ lubricant. Δ 1 Pitch diameter relief the radial reduction of the pitch and/ or major diameter behind the cutting edge of the tap. The relief confers cutting properties and provides clearance between the part being threaded and the tap threads. Δ Chamfer relief the radial reduction of the major diameter on the tap chamfer behind the cutting edge. The chamfer relief confers cutting properties to the tap. ε Spiral flute angle the angle formed by the flutes and the tap axis.
DIE TERMINOLOGY
h 1
d 1 nominal diameter d 2 outside diameter h 1 thickness
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