A cutting insert has opposing first and second end surfaces, and a peripheral side surface (connecting the end surfaces. A central axis penetrates the two end surfaces. The peripheral sure surface includes an outwardly inclined first side surface part related to a major cutting edge and a second side surface part related to a minor cutting edge. The outwardly inclined first side surface part gradually extends outward from the cutting insert, heading from the first end surface to the second end surface. When a second virtual plane, which is substantially perpendicular to the central axis and passes through the major cutting edge, is defined, an inwardly inclined part, on a back side of the cutting edge, of the second end surface is inclined so as to become more distant from the second virtual plane, heading from the outwardly inclined first side surface part to the central axis.

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 of an embodiment includes an upper surface including a first upper cutting edge and a second upper cutting edge, a lower surface including a first lower cutting edge and a second lower cutting edge, and a side surface. The side surface includes a first surface extending from the second upper cutting edge, a second surface extending from the first lower cutting edge, a third surface extending from the first upper cutting edge, and a fourth surface extending from the second lower cutting edge. The first surface and the fourth surface are parallel to a central axis. The second surface is inclined so as to depart from the central axis as going from the lower surface toward the upper surface. The third surface is inclined so as to depart from the central axis as going from the upper surface toward the lower surface.

An insert includes a rake angle set corresponding to the hardness of a material to be cut and that can suppress an increase in the material cost even when the strength of a cut edge section is increased. The insert has a polygonal shape and includes a cutting edge portion on at least one side of the polygonal shape. The cutting edge portion includes a rake face having a convex formed on one of opposite surfaces in the thickness direction a flank face having a concave formed on a surface intersecting with the one surface in the thickness direction and a concave cutting edge that is formed between the rake face and the flank face.

A reversible cutting insert for milling has first and second cutting edges formed at the transitions from the top and bottom surfaces to a lateral face. The cutting insert has a 4-fold rotational symmetry. A reference plane extends perpendicular to the axis of symmetry. The cutting edges have four cutting edge portions. One cutting edge portion is a main edge and a wiper edge that are connected by a rounded cutting corner. The first and second cutting edges are at the greatest distance from the reference plane in the region of the cutting corners. Main and wiper clearance faces directly adjoin an assigned main edge and wiper edge, respectively, in the circumferential lateral face. Exterior angles between the main clearance faces and the reference plane are greater than exterior angles between the wiper clearance faces and the reference plane.

Provided is a cutting insert that can suppress damage of a corner cutting edge. The cutting insert has an approximately polygonal shape, and is constituted of a main cutting edge and a corner cutting edge connected to the main cutting edge. The cutting insert includes: a first side face portion that is connected to the main cutting edge, has a negative clearance angle, and is formed such that height thereof increases gradually in a direction of approaching the corner cutting edge; and a second side face portion that is connected to the corner cutting edge, has a negative clearance angle, and has height that is greater than the first side face portion.

A face milling tool includes a tool body having a central rotation axis around which the tool is rotatable, and at least one insert seat formed in a transition between a front end and an envelope surface of the tool. The tool further includes at least one cutting insert mounted in the insert seat, the cutting insert having an upper side defining an upper extension plane, a cutting edge extending around the circumference of the upper side, and a lower side defining a lower extension plane directed towards the bottom support surface of the insert seat. A center axis extends perpendicularly through the upper and the lower extension planes. The tool is configured such that a main cutting edge portion is at an entering angle κ smaller than 80° and such that the upper extension plane is at a radial tipping-in angle −60°≦γ.sub.f≦−25° and at an axial tipping-in angle −20°≦γ.sub.m≦0°, such that an angle of inclination λ of the main cutting edge portion is within the range 15°≦λ≦50°.

A cutting insert has an upper surface, a lower surface, a side surface connecting the upper and lower surfaces. An intersecting edge between the upper surface and the side surface is provided with a cutting edge. The cutting edge has, in order, a second major cutting edge, a first major cutting edge, a corner cutting edge connected to these major cutting edges, and a flat cutting edge. An obtuse interior first angle (θ) is formed by the second and first major cutting edges. A interior second angle (α) formed by the flat cutting edge and the first major cutting edge is larger than an interior third angle (β) formed by the flat cutting edge and the second major cutting edge. A land is provided adjacent to the first major cutting edge, a width of the land increasing toward the first corner cutting edge.

A double-sided cutting insert for milling which has eight main cutting edges and eight wiper edges. The cutting insert includes top and bottom faces and four side faces. Each side face includes first and second sub-faces inclined with respect to each other. The first sub-face has a main cutting edge adjacent to the top face and a wiper edge adjacent to the bottom face. The second sub-face has a wiper edge adjacent to the top face and a main cutting edge adjacent to the bottom face. The wiper edge of the second sub-face is inclined inwardly relative to the cutting insert with respect to the main cutting edge of the first sub-face. The wiper edge of the first sub-face is inclined inwardly relative to the cutting insert with respect to the main cutting edge of the second sub-face.

A cutting insert is suitable for 90° shoulder milling. The cutting insert includes two end surfaces: first and second end surfaces; a peripheral side surface extending therebetween; and a cutting edge formed at an intersecting ridge portion between the first end surface and the peripheral side surface. The cutting edge is formed so that the first end surface functions as a rake face and a part of the peripheral side surface functions as a flank. A side surface portion of the peripheral side surface adjacent to at least a part of the cutting edge includes a first flank portion adjacent to the cutting edge, a second flank portion, a third flank portion, and a fourth flank portion in this order from the first end surface side toward the second end surface side.