A cutting insert for a milling tool, having a first side, a second side which is identical to the first side and a circumferential surface which extends between the first and the second sides, with a bore which extends along a bore axis. The cutting insert is 120 rotationally symmetrical with respect to the bore axis and comprises on each of the first side and the second side three identically formed cutting regions, respectively, which are situated at a transition between the first side and the circumferential surface or at a transition between the second side and the circumferential surface, respectively Each of the in total six cutting regions comprises a first rectilinear cutting edge, a second rectilinear cutting edge, and a third arcuate cutting edge, wherein a first end of the first cutting edge is connected to a first end of the third cutting edge, and a first end of the second cutting edge is connected to a second end of the third cutting edge, wherein the first and the second cutting edges are of same length. The cutting insert comprises on the first side a first contact surface which extends orthogonally to the bore axis and lies in a first contact plane, and on the second side comprises a second contact surface which extends orthogonally to the bore axis and lies in a second contact plane, and wherein each of the first cutting edges are connected at their second ends, which are located opposite the first ends, to one of a total of six arcuate edges, a vertex of which is located between the first and the second contact planes.

A ridgeline between the top surface and the side surface includes: a nose cutting edge portion having a curved line shape, the nose cutting edge portion having a first end and a second end opposite to the first end; a major cutting edge portion contiguous to the first end; and a wiper cutting edge portion contiguous to the second end. The top surface includes: a first rake face contiguous to the wiper cutting edge portion; a second rake face contiguous to the major cutting edge portion; and a third rake face contiguous to the nose cutting edge portion and contiguous to each of the first rake face and the second rake face. A boundary line between the second rake face and the third rake face is separated from the first end and is contiguous to the major cutting edge portion.

A cutting insert includes first and second polygonal surfaces and a plurality of side surfaces. A corner edge that has a corner rake surface on the first polygonal surface is formed at a first corner portion, and a main cutting edge is formed from the corner edge to a second corner portion. The main cutting edge includes, at least on a corner edge side, a rake angle gradual increase region where a rake angle of a main rake surface gradually increases to a positive angle side as going from a first end portion of the corner edge toward a second corner portion side.

A cutting tool including: a tool body (2) provided with an insert support seat (5) including a major seat surface (5a) that supports a bearing surface of a cutting insert, a plurality of seat side surfaces (5b, 5c) that supports side surfaces of the cutting insert at different positions, and a thinned portion (5d) continuous with the major seat surface and the seat side surfaces; and a cutting insert attached to the insert support seat, wherein a ridge at a position where the major seat surface and the thinned portion intersect, a ridge at a position where the seat side surface and the thinned portion intersect, and a ridge at a position where the thinned portions continuous with each other intersect are each formed of a convex arc curved surface.

Provided is a cutting insert capable of suppressing edge fracture when a work having high hardness is machined. A cutting insert includes two end surfaces having a plurality of corner parts and opposed to each other, a peripheral side surface extending between the two end surfaces, and a cutting edge formed at an intersecting edge between at least one of the two end surfaces and the peripheral side surface. The cutting edge has at least a first corner edge, a second corner edge, a major cutting edge, and an end cutting edge. The end cutting edge has a circular-arc shape, which projects outward, as viewed from the side of the end surface. The end cutting edge has a width which is from 15% to 50% of the width of the cutting insert. The end cutting edge has an arc radius which is from to 1/1 of the width of the cutting insert.

An indexable cutting insert has a first corner edge forming a front tip of a cutting edge portion configured to project furthest in the direction of an axis of rotation of an end mill tool receiving the insert. A major cutting edge is descending to come closer to the lower surface of the insert along its extension away from the first corner edge. The minor cutting edge extends from the first corner edge while descending from a point of the cutting edge portion most distant to the lower surface all the way to an inner corner of the insert and has a length of 80%-95% of the length of the major cutting edge including a second corner edge in a side elevation view of the cutting insert.

A cutting insert has an insert major body which includes two hexagonal faces facing each other and six side faces arranged around the two hexagonal faces, and is rotationally symmetrical at 120 intervals about an insert center line passing through centers of the two hexagonal faces and inversely symmetrical in front and back with respect to the two hexagonal faces, wherein a major cutting edge and an minor cutting edge are alternately formed in a circumferential direction in the single hexagonal face at twelve intersecting ridgeline portions at which the hexagonal faces and the side faces intersect, the major cutting edge is formed to be located at an intersecting ridgeline portion with one hexagonal face while the minor cutting edge is formed to be located at an intersecting ridgeline portion with the other hexagonal face at a single side face.

A cutting insert for a rotary cutting tool has a second surface that includes a second seating surface having a shape of a flat surface. The first cutting edge has a first main cutting edge portion and a first sub cutting edge portion. The second cutting edge has a second main cutting edge portion and a second sub cutting edge portion. When viewed in a direction from the first surface toward the second surface, at least a portion of the second sub cutting edge portion is located outside the first main cutting edge portion, and at least a portion of the first sub cutting edge portion is located outside the second main cutting edge portion. When viewed in the direction from the first surface toward the second surface, each of the first sub cutting edge portion and the second sub cutting edge portion has a shape of a curved line.

A cutting insert (1) has a first end surface (2); a second end surface (3) opposing the first end surface; and a peripheral side surface (4) connecting the first and second end surfaces. A cutting edge (6) extends along an intersecting edge between the first end surface and the peripheral side surface. A land (20) is formed in the first end surface and extends along the cutting edge. At least one groove (18) is formed in the peripheral side surface, each groove forming an opening in the first end surface and separating the cutting edge into a plurality of portions. In a plan view of the first end surface, a portion of the land adjacent to an end area (S) of the groove, has a greater width than a width of a portion of the land which is distant from the groove.

Provided is an insert for being mounted on a tool holder. The insert includes three substantially right-angled corners along a perimeter, a main cutting edge, a sub cutting edge, and a flat lower surface. A clearance angle of a second end main side surface forms an obtuse angle with respect to a lower surface, and a clearance angle of a second end sub side surface forms an obtuse angle with respect to the lower surface. A clearance angle of a first end main side surface forms a right angle with respect to the lower surface, and a clearance angle of a first end sub side surface forms a right angle with respect to the lower surface.