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 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 (10) for a tool (100) for machining a workpiece. The cutting insert (10) is a four-bladed cutting insert which is in the form substantially of a rhomboid. The cutting insert (10) has two identical, oppositely arranged base sides (14a, 14b) and four identical main sides (16a-16d) which extend between the two base sides (14a, 14b). Each of the four main sides (16a-16d) comprises a rectilinear main cutting edge (12a-12d) and a rectilinear secondary cutting edge (26a-26d) which is arranged transversely thereto. The main and secondary cutting edges (12a-12d) and (26a-26d) of each main side (16a-16d) lie in each case in a common cutting plane which is aligned parallel to a contact surface (28a-28d) which is also provided on the main sides (16a-16d).

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 may include a first surface. The first surface may include a first side, a second side, a first corner, a land surface and an inclined surface. The land surface may include a first land surface, a second land surface and a corner land surface. The first land surface may be located along the first side. The second land surface may be located along the second side. The corner land surface may be located along the first corner. The first land surface may include a part thereof where a first land angle increases as going away from the first corner. The corner land surface may include a part thereof where a corner land angle increases as going away from the first side.

A single-sided four-way indexable cutting insert includes a positive basic shape, a rake surface, a peripheral surface including four side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has an imaginary square frustum which defines a square base containing the cutting insert's base bearing surface, and further defines four isosceles trapezoid side surfaces respectively containing the cutting insert's four side abutment surfaces. A material volume V.sub.F of the cutting insert and a void volume V.sub.S of the insert fulfill the condition V.sub.S/V.sub.F0.25.

A cutting insert for a milling tool including an upper side having a central surface, a lower side, a peripheral side surface, and a cutting edge formed between the upper side and the peripheral side surface. The cutting edge having a positively inclined main cutting edge projecting at least partly above the central surface. The upper side includes a rake surface extending inside of and along the at least one cutting edge, sloping downward toward the central surface. A plateau, elevated with respect to the central surface and extending along the main cutting edge, is formed inside the rake surface. A transition between the rake surface and the plateau extends at an angle .sub.2 with respect to an upper extension plane, wherein .sub.2>0.

A single-sided four-way indexable cutting insert includes a positive basic shape, a rake surface, a peripheral surface including four side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has an imaginary square frustum which defines a square base containing the cutting insert's base bearing surface, and further defines four isosceles trapezoid side surfaces respectively containing the cutting insert's four side abutment surfaces. A material volume V.sub.F of the cutting insert and a void volume V.sub.S of the insert fulfill the condition V.sub.S/V.sub.F0.25.

A cutting insert (10) for a tool (100) for machining a workpiece. The cutting insert (10) is a four-bladed cutting insert which is in the form substantially of a rhomboid. The cutting insert (10) has two identical, oppositely arranged base sides (14a, 14b) and four identical main sides (16a-16d) which extend between the two base sides (14a, 14b). Each of the four main sides (16a-16d) comprises a rectilinear main cutting edge (12a-12d) and a rectilinear secondary cutting edge (26a-26d) which is arranged transversely thereto. The main and secondary cutting edges (12a-12d) and (26a-26d) of each main side (16a-16d) lie in each case in a common cutting plane which is aligned parallel to a contact surface (28a-28d) which is also provided on the main sides (16a-16d).

A cutting insert of the present disclosure includes a top surface, a bottom surface, a side surface, and a corner cutting edge, a first cutting edge, a second cutting edge and a third cutting edge formed at a ridge line formed by the side surface and the top surface. The corner cutting edge has a first end and a second end. The first cutting edge extends from the first end in a first direction. The second cutting edge extends from the second end in a second direction. The third cutting edge extends from the second cutting edge in a third direction. The top surface has a first rake face adjacent to the first cutting edge, a second rake face adjacent to the second cutting edge, and a third rake face adjacent to the third cutting edge.