A cutting insert of a substantially horizontal cylindrical segment shape and having top and bottom surfaces with a circular segment shape. The cutting insert has a convex side and a flat side, a top cutting edge which is formed where the convex side and the top surface meet, and a bottom cutting edge which is formed where the convex side and the bottom surface meet. The cutting insert includes a hole extending from the convex side towards the flat side. The hole is positioned at a center of a surface of the flat side.

A cutting insert suitable for a small-diameter milling tool is provided. A cutting insert has a rake face, a bottom surface, a circumferential side surface, and a through hole. A first ridgeline at which the rake face and the circumferential side surface intersect each other includes a first main cutting edge, and a first corner cutting edge connected to a tip of the first main cutting edge. The bottom surface includes a first bottom surface that comes closer to the rake face gradually toward a side at which the first main cutting edge is located when viewed from a central axis of the through hole, and a second bottom surface that comes closer to the rake face gradually toward a side opposite to the first main cutting edge when viewed from the central axis. A distance between a virtual intersection line, at which a first virtual surface formed by extending the first bottom surface and a second virtual surface formed by extending the second bottom surface intersect each other, and the first main cutting edge decreases from a tip side, at which the tip of the first main cutting edge is located, toward an end side, at which an end opposite to the tip is located, in an extending direction of the first main cutting edge.

A cutting insert according to one embodiment includes: a rake face; a flank face continuous to the rake face; and a cutting edge constituted of a ridgeline between the rake face and the flank face. A coolant flow path is provided inside the cutting insert. One end portion of the coolant flow path opens in the flank face to form a coolant ejection hole. The flank face is provided with a coolant guide groove extending from the coolant ejection hole toward the cutting edge with a base end portion of the coolant guide groove being connected to the coolant ejection hole and with a front end portion of the coolant guide groove being disposed at a position close to the cutting edge relative to the base end portion.

A milling cutting insert has a substantially triangular shape. The cutting insert contains a top side, an underside, and circumferential side surfaces extending between the top side and the underside. Cutting edges are formed at the transition of the circumferential side surfaces to the top side and/or the underside. On the circumferential side surfaces at least two discrete planar abutment surfaces are formed for positioning the cutting insert in a tool holder. The at least two discrete planar abutment surfaces are inclined with respect to each other at an outer angle of between 190° and 220° and the abutment surfaces are spaced from each other with respect to the circumferential direction of the cutting insert.

In one embodiment, a cutting tool includes an insert that includes a cutting edge at at least one part of a portion where two surfaces intersect. The cutting tool further includes a holder capable of rotating about a rotational axis. The holder includes a pocket including: a placement portion where the insert is positioned; and a cutout portion is adjacent to the placement portion and positioned further forward in a rotational direction than the placement portion. The holder further includes an inflow port that opens at at least one part of the holder, a first flow path positioned in the interior of the holder, and an outflow port positioned at the pocket. The cutout portion includes a recessed portion.

A front and back chamfering rotary milling cutter includes a cutter body including an insert pocket and a star-shaped indexable cutting insert releasably retained in the pocket. The cutting insert has star-shaped upper and lower surfaces connected by a peripheral surface intersecting each of the upper and lower surfaces. The cutting insert includes a plurality of circumferentially alternating inner and outer corner portions. A cutting portion is defined by each outer corner portion together with an adjacent first inner corner portion rotationally forward thereof and an adjacent second inner corner portion located rotationally rearward thereof. Each cutting portion includes a front chamfering cutting edge extending from the outer corner portion to the first inner corner portion and a back chamfering cutting edge extending from the outer corner portion to the second inner corner portion.

A mounting seat bottom surface facing a holder rotation direction; a first mounting seat wall surface (3b) facing an outer peripheral side of the holder main body (1), and a first relief portion (3d) on a corner portion where they intersect, are formed on an outer peripheral portion of a tip of a holder main body (1) rotated in a direction around an axis, on the inner peripheral side of the first mounting seat wall surface (3b), an inclined face (6) is formed in a range from an end edge (3b1) of the first mounting seat wall surface (3b) to 2 mm or less in the inner peripheral side, and the inclined face (6) being retracted toward the posterior end side in the axial direction as being extended toward the inner peripheral side, and an inclination angle θ is 20° or more and 50° or less.

A mounting seat bottom surface facing a holder rotation direction; a first mounting seat wall surface (3b) facing an outer peripheral side of the holder main body (1), and a first relief portion (3d) on a corner portion where they intersect, are formed on an outer peripheral portion of a tip of a holder main body (1) rotated in a direction around an axis, on the inner peripheral side of the first mounting seat wall surface (3b), an inclined face (6) is formed in a range from an end edge (3b1) of the first mounting seat wall surface (3b) to 2 mm or less in the inner peripheral side, and the inclined face (6) being retracted toward the posterior end side in the axial direction as being extended toward the inner peripheral side, and an inclination angle θ is 20° or more and 50° or less.

A milling tool includes a rotatable tool body, a cutting insert, and first and second coolant outlets. The rotatable tool body is configured to rotate around an axis. The rotatable tool body includes a circumferential outer surface with a pocket defined therein. The pocket includes a seating surface. The cutting insert is disposed within the pocket. The cutting insert includes a seating face and a rake face opposed to the seating face. The seating face is disposed against the seating surface. The first coolant outlet is disposed in or attached to the rotatable tool body disposed on an opposite side of the rake face as the seating face. The second coolant outlet is disposed in or attached to the rotatable tool body disposed on an opposite side of the seating face as the rake face. The second coolant outlet is disposed outside of and adjacent to the seating face.

A milling tool includes a rotatable tool body, a cutting insert, and first and second coolant outlets. The rotatable tool body is configured to rotate around an axis. The rotatable tool body includes a circumferential outer surface with a pocket defined therein. The pocket includes a seating surface. The cutting insert is disposed within the pocket. The cutting insert includes a seating face and a rake face opposed to the seating face. The seating face is disposed against the seating surface. The first coolant outlet is disposed in or attached to the rotatable tool body disposed on an opposite side of the rake face as the seating face. The second coolant outlet is disposed in or attached to the rotatable tool body disposed on an opposite side of the seating face as the rake face. The second coolant outlet is disposed outside of and adjacent to the seating face.