A rotary cutting tool that implements a chip space in proportion to a feed-per-tooth is proposed. The rotary cutting tool includes a cutting part in which a plurality of cutting teeth and flutes are alternately formed, wherein a cross-section of the cutting part perpendicular to a central axis is divided into a plurality of cutting tooth spaces defining a section between cutting edges of adjacent cutting teeth on the basis of the central axis, such that all of the cutting tooth spaces are designed in different sizes, or some of the plurality of cutting tooth spaces are set in different sizes from the other cutting tooth spaces.

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 long twist drill includes a shank and a drill body having a drill tip (16). The twist drill has a length L and an outer diameter D, and has a cemented carbide or high speed steel substrate and a coating of at least one layer. The quota L/D is at least 16. The twist drill has two cutting segments at the tip and two flutes chip. The twist drill is provided with holes for fluid opening in the tip. The twist drill has an axial web thinning angle GAA, which is 40 to 50°. The twist drill further has a web that back tapers such that a web diameter gets smaller in a direction away from the tip towards the shank within an axial distance.

A drill according to an embodiment includes a bar-shaped drill body extending along a rotation axis, a cutting edge located at a front end of the drill body, and a first flute extending spirally from the cutting edge toward a rear end of the drill body. The first flute includes a first region which is located close to the front end and has a helix angle θ1, and a second region which is located closer to the rear end than the first region and has a helix angle θ2 smaller than the helix angle θ1. The second region includes an elongated protruding part along the first flute.

A rotary cutting tool that implements a chip space in proportion to a feed-per-tooth is proposed. The rotary cutting tool includes a cutting part in which a plurality of cutting teeth and flutes are alternately formed, wherein a cross-section of the cutting part perpendicular to a central axis is divided into a plurality of cutting tooth spaces defining a section between cutting edges of adjacent cutting teeth on the basis of the central axis, such that all of the cutting tooth spaces are designed in different sizes, or some of the plurality of cutting tooth spaces are set in different sizes from the other cutting tooth spaces.

A drill according to an embodiment includes a bar-shaped drill body extending along a rotation axis, a cutting edge located at a front end of the drill body, and a first flute extending spirally from the cutting edge toward a rear end of the drill body. The first flute includes a first region which is located close to the front end and has a helix angle 1, and a second region which is located closer to the rear end than the first region and has a helix angle 2 smaller than the helix angle 1. The second region includes an elongated protruding part along the first flute.

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 step drill includes a stepped cone formed with a tip and a bottom, a shank extending from the bottom, and steps formed between the tip and the bottom. The stepped cone includes a transitional portion formed on one of the steps. There is a first length between the transitional portion and the tip. There is a second length between the transitional portion and the bottom. The stepped cone includes four helical grooves. The first and second helical grooves are located opposite to each other. The third and fourth helical grooves are located to each other. The first and second helical grooves extend from the tip. The third and fourth helical grooves extend from the transitional portion to the bottom.