Provided is a cutting tool capable of improving both the biting property to a work material and the chip discharge property. The cutting tool includes a drill body rotated about a central axis, four or more cutting edges formed on one end portion of the drill body to face a forward side of a rotation direction, and a flute groove that is formed between the cutting edges adjacent to each other in a circumferential direction and extends substantially spirally along the central axis. (1) The one end portion includes a first tip portion that includes the central axis and has a first tip angle, and a second tip portion that extends from the first tip portion to an outer peripheral edge of the drill body and has a second tip angle larger than the first tip angle, and (2) the drill body includes a first core thickness portion that is formed in such a manner that a core thickness thereof gradually decreases from the one end portion to the other end portion, and a second core thickness portion that is formed in such a manner that a core thickness thereof is constant from the first core thickness portion toward the other end portion.

A drill has a body extended along a rotation axis from a first end toward a second end. The body has an outer peripheral surface, a cutting edge, a flank surface, and a flute. The cutting edge has a first cutting edge, a second cutting edge extended from the first cutting edge, and a third cutting edge extended from the second cutting edge. The flank surface has a first flank surface which is located along the first cutting edge and has a first clearance angle, a second flank surface which is located along the second cutting edge and has a second clearance angle, and a third flank surface which is located along the third cutting edge and has a third clearance angle. The second clearance angle is smaller than each of the first clearance angle and the third clearance angle.

In this drill, a main cutting edge is formed on a tip-side ridge portion of a chip discharge flute (6) formed on an outer periphery of a tip portion of a drill body, a thinning edge is formed on a tip-side ridge portion of a thinning portion having a concave groove shape formed on a tip inner peripheral portion of the chip discharge flute, when viewed from a twist direction of the chip discharge flute, a radius of an the chip discharge flute inscribed circle is in a range of 0.3×D2 to 0.7×D2 with respect to a diameter D2 of a second circle; in the thinning portion, a radius (R2) of a thinning inscribed circle (C6) is in a range of 0.3×d to 0.7×d with respect to a core diameter (d) when viewed in a thinning direction.

A three-flute drill includes a body, discharge grooves, cutting edges, thinning edges and gash portions. The discharge grooves are provided in an outer peripheral surface of the body. The cutting edges are provided on ridge sections between inner faces of the discharge grooves and flanks of the body. The thinning edge extends from an end of the cutting edge toward a radially inner side. The gash portion includes an R portion and a straight portion. A first ridge line between the R portion and the flank extends while curving toward a rotation direction, from an end of the thinning edge toward a radially outer side. A second ridge line between the straight portion and the flank extends linearly from an end of the first ridge line toward the radially outer side, and connects to the discharge groove further to the radially inner side than the outer peripheral surface.

The drill is rotatable about a central axis. The drill includes a central axis, a front end and a rear end opposite to each other in a direction along the central axis, an outer peripheral surface, a cutting edge formed at the front end and extending from the outer peripheral surface toward the central axis, a flank face contiguous with the cutting edge, a flute formed on the outer peripheral surface and extending spirally around the central axis from the front end toward the rear end, and a thinning rake face contiguous with the flute. The cutting edge has a main cutting edge extending from the outer peripheral surface and a thinning cutting edge contiguous with an end of the main cutting edge away from the outer peripheral surface. The flute includes a main rake face contiguous with the main cutting edge from the opposite side of the flank face.

A cutting head rotatable about a first axis, comprising an intermediate portion and a tip portion. The intermediate portion has a plurality of leading edges defining a cutting diameter, and the tip portion has an axially forwardmost tip point and a plurality of front surfaces with outer and inner cutting edges. An outer rake surface adjacent to each outer cutting edge has a positive outer rake angle, and an inner rake surface adjacent to each inner cutting edge has a negative inner rake angle. Each outer rake surface is disposed on a head flute intersecting one of the leading edges, and each inner rake surface is disposed on a gash intersecting one of the head flutes. Each gash extends to a gash path end point located a first distance axially rearward of the tip point, and the first distance is greater than thirty percent of the cutting diameter.

A drill head is rotated about a center axis. The drill head includes: a mounting surface that is an end face in a direction of the center axis; a tip surface that is an opposite surface to the mounting surface in the direction of the center axis; an outer peripheral surface continuous to the mounting surface and the tip surface; a cutting edge extending from the outer peripheral surface toward the center axis in the tip surface; a flute that is formed on the outer peripheral surface and extends spirally around the center axis from the tip surface to the mounting surface; and a thinning surface continuous to the tip surface and the flute. The tip surface includes: a first flank surface continuous to the cutting edge; and a second flank surface located on a side opposite to the first flank surface with the flute interposed therebetween.

A drill (1) is provided with a thinning edge (7), a gash portion (8), a coolant passage, and an oil hole (12). The thinning edge (7) is provided at a leading end portion of a body (3), and extends toward a chisel portion (9) from an inner end (51) of a cutting edge (5). A ridge line between the gash portion (8) and the flank (6) extends in a circular arc shape from an inner end of the thinning edge (7) toward an outer peripheral surface (31) of the body (3). The coolant passage is provided inside a shank and the body (3), and extends from a rear end portion of the shank toward the leading end portion of the body (3). The oil hole (12) is provided at a gash face (81) of the gash portion (8) and is an outlet of the coolant passage.

A drill has a helical flute surface, a flank face, and a thinning face. A ridgeline between the thinning face and the flank face constitutes a thinning cutting edge. The thinning cutting edge has a curved thinning cutting edge portion and a straight thinning cutting edge portion. The curved thinning cutting edge portion protrudes forward in the rotation direction. The straight thinning cutting edge portion is contiguous to the curved thinning cutting edge portion. The curved thinning cutting edge portion has a first end portion and a second end portion. The first end portion is a boundary between the curved thinning cutting edge portion and the straight thinning cutting edge portion.

Provided is a cutting tool capable of improving both the biting property to a work material and the chip discharge property. The cutting tool includes a drill body rotated about a central axis, four or more cutting edges formed on one end portion of the drill body to face a forward side of a rotation direction, and a flute groove that is formed between the cutting edges adjacent to each other in a circumferential direction and extends substantially spirally along the central axis. (1) The one end portion includes a first tip portion that includes the central axis and has a first tip angle, and a second tip portion that extends from the first tip portion to an outer peripheral edge of the drill body and has a second tip angle larger than the first tip angle, and (2) the drill body includes a first core thickness portion that is formed in such a manner that a core thickness thereof gradually decreases from the one end portion to the other end portion, and a second core thickness portion that is formed in such a manner that a core thickness thereof is constant from the first core thickness portion toward the other end portion.