A trigonal cutting insert for a shoulder milling tool includes an upper side, an opposite lower side and a peripheral side surface. A plurality of indexable cutting edges extend along corners of the cutting insert, each cutting edge having a main cutting edge, a corner cutting edge, and a surface-wiping secondary cutting edge. The upper side includes a recessed central surface, and a plurality of positively inclined rake surfaces having a main rake surface portion, a corner rake surface portion, and a secondary rake surface portion. A concave indentation is formed in the corner rake surface portion and in at least an initial part of the main rake surface portion adjacent to the corner rake surface portion, wherein the concave indentation has an elongated shape.

An insert may include a first surface, a second surface, a ridge line located at an intersection of the first surface and the second surface. The first surface may include a first corner, a first side and a second side. The ridge line may include a corner cutting edge located on the first corner, a first cutting edge located on the first side, and a second cutting edge located on the second side. The first surface may further include a first region located from the first cutting edge toward a midportion of the first surface, a second region located from the second cutting edge toward the midportion of the first surface, and a concave part located on at least one of the first region and the second region.

A cutting insert includes an end cutting edge, a first major cutting edge, and a second major cutting edge. The height of the end cutting edge relative to an imaginary plane orthogonal to a central axis of a through-hole is fixed. The height of the first major cutting edge relative to the imaginary plane increases, when viewed from a side, moving away from the end cutting edge. The height of the second major cutting edge relative to the imaginary plane decreases, when viewed from a side, moving away from the first major cutting edge. When viewed from a side, the angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the second major cutting edge is greater than an angle of inclination, relative to the imaginary plane, of an imaginary line connecting both ends of the first major cutting edge.

A cutting insert includes a base body and a coating layer, and also includes a rake surface, a flank surface, and a cutting edge located along an intersecting ridge therebetween. The rake surface includes an outer peripheral part and a middle part protruded relative to the outer peripheral part. The middle part includes a constraining surface. The outer peripheral part includes a first breaker part, a second breaker part, and the third breaker part adjacent to the constraining surface. The constraining surface is configured by the base body and the coating layer does not exist at the constraining surface. A skewness Rsk of a roughness curve at the constraining surface is −1.5 μm to −0.5 μm. A skewness Rsk at the third breaker part is −0.2 μm or less. The skewness Rsk at the constraining surface is smaller than the skewness Rsk at the third breaker part.

An insert may include a first surface, a second surface, a ridge line located at an intersection of the first surface and the second surface. The first surface may include a first corner, a first side and a second side. The ridge line may include a corner cutting edge located on the first corner, a first cutting edge located on the first side, and a second cutting edge located on the second side. The first surface may further include a first region located from the first cutting edge toward a midportion of the first surface, a second region located from the second cutting edge toward the midportion of the first surface, and a concave part located on at least one of the first region and the second region.

An insert may include a first surface, a second surface, a ridge line located at an intersection of the first surface and the second surface. The first surface may include a first corner, a first side and a second side. The ridge line may include a corner cutting edge located on the first corner, a first cutting edge located on the first side, and a second cutting edge located on the second side. The first surface may further include a first region located from the first cutting edge toward a midportion of the first surface, a second region located from the second cutting edge toward the midportion of the first surface, and a concave part located on at least one of the first region and the second region.

A trigonal cutting insert for a shoulder milling tool includes an upper side, an opposite lower side and a peripheral side surface. A plurality of indexable cutting edges extend along corners of the cutting insert, each cutting edge having a main cutting edge, a corner cutting edge, and a surface-wiping secondary cutting edge. The upper side includes a recessed central surface, and a plurality of positively inclined rake surfaces having a main rake surface portion, a corner rake surface portion, and a secondary rake surface portion. A concave indentation is formed in the corner rake surface portion and in at least an initial part of the main rake surface portion adjacent to the corner rake surface portion, wherein the concave indentation has an elongated shape.

An insert may include a first surface, a second surface, a ridge line located at an intersection of the first surface and the second surface. The first surface may include a first corner, a first side and a second side. The ridge line may include a corner cutting edge located on the first corner, a first cutting edge located on the first side, and a second cutting edge located on the second side. The first surface may further include a first region located from the first cutting edge toward a midportion of the first surface, a second region located from the second cutting edge toward the midportion of the first surface, and a concave part located on at least one of the first region and the second region.

An indexable rotary cutting tool and insert is capable of performing a high-accuracy cutting process with high efficiency. A twist angle of an outer peripheral cutting edge of the tool has a positive value, an axial rake angle of the cutting edge of a corner R of the tool at a boundary point between the cutting edge of the corner R and the outer peripheral cutting edge has a positive value, the axial rake angle of the cutting edge of the corner R at a reference point has a negative value, and the radial rake angle at least between the boundary point and the reference point in an entire edge length region of the cutting edge of the corner R has a negative value. The radial rake angle at the reference point is smaller than the radial rake angle at the boundary point.

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.