Drill

A drill, comprising:

• front and rear ends;
• a centre axis (C) extending between the front and rear ends and peripheral envelope surface that is concentric with the centre axis, wherein the front end is formed as a tip having an obtuse nose angle (c);
• two chip flutes countersunk in the peripheral envelope surface, which flutes are situated between a pair of bars and run helicoidally at a certain pitch angle (φ) around a central core, and individually are delimited by a chute-shaped flute wall situated between a pair of parallel border edges, a first border edge heading in the direction of rotation of the drill and a second border edge trailing,
• wherein:
• a) a cutting edge extends from the centre axis (C) to the periphery and includes a main edge formed by an intersection between the individual chip flute and a clearance surface included in the tip and a center cutting edge oriented at the nose angle (ε),
• b) the flute wall includes a frontal surface that is situated closest to the first border edge and extends axially rearward from the main edge included in the cutting edge, and a trailing surface situated closest to the second border edge, which trailing surface transforms into the frontal surface via a concavely arched bottom surface and extends rearward from a web thinning formed in the tip and located adjacent to the centre cutting edge, which transforms into the main edge at a knee, wherein the centre cutting edge is shorter than the main edge and wherein the centre cutting edge intersects the centre axis at a first axial position and a projection of an imaginary line extending from the main edge intersects the centre axis at a second axial position that is different from the first axial position,
• c) a radial angle (6) between the frontal surface and a radial reference line (RL1) between the centre axis (C) and the first border edge is positive so far that the frontal surface is situated rotationally behind the reference line,
• d) the individual chip flute has an opening angle (α)—counted as the angle between the first reference line (RL1) and a second reference line (RL2) between the centre axis (C) and the second border edge, with which an angle of divergence (β) of the individual bar forms the supplementary angle,
• e) the core has a diameter (DC) that amounts to at most 22% of the drill diameter (D),
• f) the angle of divergence (β) of the bar is greater than the opening angle (α) of the chip flute,
• g) the frontal and trailing surfaces of the individual flute wall are delimited from the bottom surface via helicoidal boundary lines located at a change in radii of curvature between the frontal and trailing surfaces and the bottom surface, and the frontal and trailing surfaces have radii of curvature (r1, r2) as viewed in a plane perpendicular to the centre axis that are at least three times greater than the radius (r3) of the bottom surface, and
• h) a first boundary line, positioned closest to the first border edge, meeting the main edge in a meeting point that divides the same into two edge segments, an inner edge segment positioned closest to the centre cutting edge has a smaller radius of curvature than an outer edge segment positioned furthest from centre cutting edge, and
• wherein the centre cutting edge and the outer edge segment of the main edge are parallel within 3 degrees to each other.