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.

An indexable cutting insert has opposing upper and lower end surfaces, and a peripheral surface including three side surfaces and three corner surfaces. Each corner surface intersects the upper end surface to form an upper cutting edge, and each side surface has a locating surface. The lower end surface has three radially outward facing lower abutment surfaces. The three locating surfaces define a first imaginary triangle having three first bisector planes and three locating planes, and the three lower abutment surfaces define a second imaginary triangle having three second bisector planes. None of the first and second bisector planes are coplanar, and each locating plane intersects two of the upper cutting edges. For each index position of the cutting insert in an insert receiving pocket of a cutting tool, one of the locating surfaces and one of the lower abutment surfaces is in contact with pocket walls thereof.

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.

Provided is a structure for improving accuracy in attaching a cutting tool to a body and making it possible to increase the number of blades while the cutting tool is mounted on the body. A cutting insert 1 includes: an upper surface 10 that has a shape with a lengthwise direction LD and a widthwise direction SD; a lower surface that is located opposite to the upper surface 10; a peripheral side surface 30 that is formed so as to connect the upper surface 10 and the lower surface; cutting edges 51 and 52 that are respectively formed on an intersecting ridge line of the upper surface 10 and the peripheral side surface 30, and on an intersecting ridge line of the lower surface and the peripheral side surface 30, and each have a curved ridge line that extends in a lengthwise direction thereof; and a through hole 60 that penetrates from the upper surface 10 to the lower surface. End surfaces 31 and 32 located in the lengthwise direction LD of the upper surface 10 and the lower surface, of the peripheral side surface 30, are respectively inclined with respect to the upper surface 10 and the lower surface, and are parallel to each other. A reference surface 33 that is located opposite to the cutting edges 51 and 52, of the peripheral side surface 30, is a flat surface that is orthogonal to the upper surface 10 and the lower surface.

A cutting insert in a non-limiting aspect of the present disclosure may include an upper surface having a polygonal shape and including a first side, a lower surface, and a lateral surface. The lateral surface may include a first lateral surface located between the first side and the lower surface. The first lateral surface may include a first region that is flat. The first region may include a first central region, a first upper region and a first lower region. The first upper region may be located closer to the upper surface than the first central region, and may have a larger width than the first central region. The first lower region may be located closer to the lower surface than the first central region, and may be a larger width than the first central region.