Screw tap and method for the production of a screw tap

A screw tap,

• a) which is rotatable about a rotational axis, and
• b) has a number of thread-cutting teeth, which respectively have a radially outer tip cutter and are disposed mutually offset, with a predefined thread pitch, in an arrangement running spirally or helically around the rotational axis,
• c) wherein, in a lead region adjoining one end of the screw tap axially to the rotational axis, the maximum radial distance of the tip cutters of the thread-cutting teeth from the rotational axis increases with increasing axial distance of the tip cutters from one end of the screw tap according to a predefined radial distance function,
• d) wherein radially is defined as perpendicular to the rotational axis and axially is defined as along or parallel to the rotational axis,
• e) wherein at least some of the thread-cutting teeth in the lead region, at least in the region of the tip cutters, respectively have a defined cutter rounding between tool face and tool flank, the curvatures of the cutter roundings and/or reduction depths of the cutter roundings being chosen, in comparison to the ideal wedge shape (20′) or to the unrounded cutting edge, respectively in dependence on
• e1) the number of thread-cutting teeth in the lead region and
• e2) the thread pitch,
• f) in which the radii of curvature of the cutter roundings of at least some of the thread-cutting teeth in the lead region are chosen, at least in the region of their tip cutters, according to the equation:
• R=f(γ3)·C·P/Z
• and the reduction depths of the cutter roundings of at least some of the thread-cutting teeth in the lead region are chosen, at least in the region of their tip cutters, according to the equation:
• a=C·P/Z,
• wherein R is the radius of curvature, 2γ3 the wedge angle, f (γ3) a function of the wedge angle 2γ3, P the thread pitch, and Z the number of thread-cutting teeth in the lead region, and C is a real number with:
• 0.75≦0.7383.

A method for the production of screw taps, which are rotatable about a rotational axis, in which:

• a) for each screw tap an associated number of thread-cutting teeth, which respectively have a radially outer tip cutter and are disposed mutually offset, with a predefined thread pitch, in an arrangement running spirally or helically around the rotational axis, is produced;
• b) wherein, in a lead region adjoining one end of the screw tap axially to the rotational axis, the maximum radial distance of the tip cutters of the thread-cutting teeth from the rotational axis increases with increasing axial distance of the tip cutters from one end of the screw tap, according to a predefined radial distance function,
• c) wherein radial is defined as perpendicular to the rotational axis and axial is defined as along or parallel to the rotational axis,
• d) wherein at least some of the thread-cutting teeth in the lead region, at least in the region of the tip cutters, are provided or produced with respectively a cutting edge rounding with defined curvature, the curvatures of the cutting edge roundings and/or the reduction depths of the rounded cutting edges, in comparison to the ideal wedge shape or unrounded cutting edge, being chosen or set respectively in dependence on:
• d1) the number of thread-cutting teeth in the lead region, and
• d2) the thread pitch, and
• d3) preferably also the increase in the maximum radial distance of the tip cutters of the thread-cutting teeth in the lead region, or on the radial distance function of the thread-cutting teeth in the lead region of the respective screw tap.