A drill according to an embodiment of the present invention has a pair of main cutting edges positioned at a front end of a drill body, a pair of first chisel edges each extending from the pair of main cutting edges toward a rotation axis, and a second chisel edge positioned between the pair of first chisel edges and intersecting with the rotation axis of the drill body. When viewing a locus of rotation of the pair of first chisel edges and a locus of rotation of the second chisel edge in a cross section taken so as to include the rotation axis, the respective locus of rotation of the pair of first chisel edges have a rectilinear shape, and respective imaginary straight lines obtained by extending the locus of rotation of the pair of first chisel edges toward the rotation axis are positioned further to a rear end side of the drill body than the locus of rotation of the second chisel edge.

A drill has a replaceable cutting head mounted to a shank in an interlocking fashion. The shank has a pocket with at least one flat, vertically-angled retention surface located closer to a rotational axis than at least one driving surface. Similarly, the cutting head has at least one vertically-angled retention surface located closer to the rotational axis of the drill than at least one driven surface. As a result of the relative locations between the surfaces with respect to the rotational axis, the stresses and fatigue imposed on the drill are minimized, thereby prolonging tool life.

A drilling tool includes at least two chip flutes and a chisel edge with a thinned region. The thinned region merges continuously into the chip flutes in such a way that the thinned region forms the end of the respective chip flute in the region of the chisel edge.

Provided is a drill suitable for high-efficiency working. A cut debris discharge groove is formed in the outer periphery of the drill body front end section rotated about the axis, and a cutting edge is formed at the front end of the drill body. The wall surface of the cut debris discharge groove, which faces the rotational direction of the drill, is formed to have a concave curve line shape in a cross-section perpendicular to the axis, the concave curve line shape extending along a first circular arc.

A drill of the present invention includes: a drill main body; a plurality of convex-arc cutting edges which are formed on a tip side of the drill main body from an outer periphery of the drill main body to a chisel edge provided near to a rotational axis; second faces which are each formed in an approximately band shape and are each formed along each of the convex-arc cutting edges on a back side of the convex-arc cutting edge in the rotational direction; third faces which are each formed to be continuous with a back side of each of the second faces in the rotational direction; and fourth faces which are each formed to be continuous with a back side of each of the third faces in the rotational direction.

A drill configured for drilling ductile materials includes a drill margin with a margin extremity adjacent to a relief surface. The drill includes a drill body and a drill head secured to the drill body via rotational coupling of the drill head on the drill body.

A drill has a central axis, a front side, a circumferential surface, at least two main edges on the front side, which reach up to the circumferential surface and merge there with secondary edges, at least two central edges extending from the end of the main edge facing away from the circumferential surface, cutting surfaces associated with the main edges and central edges, chip flutes associated with the main edges and central edges and introduced into the circumferential surface, at least one cross edge adjoined by the ends of the central edges facing away from the main edges which passes through the central axis, a point thinning and chip run-up shoulders associated with at least the cutting surfaces of the central edges. An angle of the chip run-up shoulder decreases in the region of the point thinning towards the central axis as the distance from the front side increases.

Methods of forming a drill bit or boring tool having a cutting edge that includes a pair of generally smooth curvilinear shaped portions that are positioned near the radial outer portions of the cutting edge and connected to one another by a pair of generally linear portions that traverse a longitudinal centerline of the tool.

A drill with a drill flute (12) includes symmetrical fluted lands (20) helically extend around a core, wherein grooves (18) remain between the fluted lands, said grooves having a width (72) that exceeds the spine thickness or width (24) of the fluted lands (20), and wherein the grooves (18) comprise a convex core reinforcement (22) at the groove bottom thereof. The width (24) of the fluted lands (20) at the drill head side end (16) is smaller than at the shank side end (14) of the drill helix (12), and at least increases in certain areas. The core reinforcement (22) at the drill head side end (16) is more convex than at the shank side end (14), thus has larger radii (40, 42).

A three-flute drill includes: three chip discharge flutes; and three cutting edges each having concavely-curved and convexly-curved cutting edge portions, an axially perpendicular cross-sectional view orthogonal to an axial center having first convex and concave curves respectively corresponding to the convexly-curved and concavely-curved cutting edge portions intersecting each other, in the axially perpendicular cross-sectional view, a concave amount of the first concave curve being within a range of 0.01D to 0.05D in terms of a drill cutting diameter relative to a reference line connecting an outer circumferential point, at which a drill outer circumferential portion intersects with the first convex curve, and the axial center, and in the axially perpendicular cross-sectional view, a rake chamfer width being a distance from an intersection between a straight line through the intersection and orthogonal to the reference line and the reference line, to the outer circumferential point, and being within 0.005D to 0.06D.