In a cutting tool having an indexable lay-down cutting insert with a central body portion and three circumferentially spaced apart cutting portions, the cutting insert is removably secured to an elongated holding portion of an insert holder. Each cutting portion has a cutting edge with first and second cutting end points, the cutting edge formed at the intersection of an upward facing rake surface and a radially outward facing relief surface. In a top view of the cutting insert, parallel imaginary first and second vertical planes containing the first and second cutting end points, intersect the central body portion at first and second body side points, which are located first and second cutting distances from the first and second cutting end points, respectively. Each of the first and second cutting distances is greater than twenty-five percent of the first radius of an imaginary first circle circumscribing the cutting insert.

A cutting insert may include a first surface, a second surface, a first lateral surface, a second lateral surface, a first cutting edge and a second cutting edge. The first lateral surface may include a first inclined surface located along the first cutting edge, a second inclined surface located along the first inclined surface, a third inclined surface located along the second cutting edge, a fourth inclined surface located along the third inclined surface, and a flat surface located along the second inclined surface and the fourth inclined surface. A second inclination angle of the second inclined surface may be smaller than a first inclination angle of the first inclined surface. A fourth inclination angle of the fourth inclined surface may be larger than a third inclination angle of the third inclined surface.

Provided is a cutting insert configured to be able to realize downsizing of a cutting tool. A cutting insert includes: an upper surface and a lower surface facing each other and having a plurality of corner parts; a side surface connecting the upper surface and the lower surface and forming intersecting edges with the upper surface and the lower surface, respectively; and a through hole that has a central axis extending from the upper surface to the lower surface and that is formed for penetration from the upper surface to the lower surface. A corner cutting edge arranged at a position corresponding to a corner part of the upper surface, a minor cutting edge connected to a first end of the corner cutting edge, and a major cutting edge connected to a second end of the corner cutting edge are formed on the intersecting edge between the upper surface and the side surface. A flank of the corner cutting edge and a recessed part located on the lower surface side of the flank of the corner cutting edge are formed on the side surface.

A reversible cutting insert for milling including opposing and identically or substantially identically top and bottom surfaces interconnected by a continuous peripheral side surface, with a median plane located between the top and bottom surfaces and intersecting the side surface, and an insert axis perpendicular to the median plane about which the cutting insert is indexable. Each top and bottom surface is limited by a circumferential cutting edge intersecting the side surface, the circumferential cutting edge in a top view having the shape of a truncated equilateral triangle. Each circumferential cutting edge includes three analogous sets of cutting edges exhibiting three-fold rotational symmetry about the insert axis. A first cutting edge portion intersects a first support plane.

A single-sided three-way indexable milling insert for feed milling operations, includes a positive basic shape, a rake surface, a peripheral surface including side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has a cutting edge including exactly three main cutting sub-edges and three secondary cutting sub-edges. 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.F≥0.30.

A tangential cutting insert includes two opposing main surfaces having a triangular shape, three identical side surfaces extending between the main surfaces, and at least three identical and indexable major cutting edges formed at the intersection of at least one of the main surfaces and the three identical side surfaces. Each side surface includes three flat support surfaces recessed in relation to the major cutting edge and arranged one after another in a longitudinal direction of each side surface. A first flat support surface is disposed centrally in each side surface and forms the lowermost recessed support surface in relation to the major cutting edge. Second and third flat support surfaces are located on opposite sides of the first flat support surface and extend at an obtuse angle with the first flat support surface. A milling tool having a plurality of insert seats receiving the tangential cutting insert is provided.

A single-sided three-way indexable milling insert for 90° shoulder milling operations, includes a positive basic shape, a rake surface, a peripheral surface including side abutment surfaces, a base bearing surface and a screw hole connecting the rake and base bearing surfaces. The insert has three main cutting edges which lie along an imaginary equilateral triangle. A material volume V.sub.F of the cutting insert and a void volume V.sub.S of the insert's screw hole fulfill the condition V.sub.S/V.sub.F≥0.30.

A cutting insert includes a first end surface and a second end surface, in which a first peripheral side surface includes a first rake surface adjacent to a first main cutting edge and a first concave surface connected to the second end surface and formed to be recessed from the first rake surface toward a central axis of a through hole, and the first concave surface has a first restraint surface provided at a position where a distance between the first restraint surface and a second main cutting edge is smaller than a distance between the central axis of the through hole and the second main cutting edge, when viewed from a direction parallel to the central axis of the through hole.

A cutting insert may include a first surface, a second surface, a first lateral surface, a second lateral surface, a first cutting edge and a second cutting edge. The first lateral surface may include a first inclined surface located along the first cutting edge, a second inclined surface located along the first inclined surface, a third inclined surface located along the second cutting edge, a fourth inclined surface located along the third inclined surface, and a flat surface located along the second inclined surface and the fourth inclined surface. A second inclination angle of the second inclined surface may be smaller than a first inclination angle of the first inclined surface. A fourth inclination angle of the fourth inclined surface may be larger than a third inclination angle of the third inclined surface.

An indexable roughing end mill capable of suppressing generation of chattering is provided. When the positions of cutting inserts (40) arranged in each spiral groove (28) are defined as a first segment to an n.sup.th segment (where n is an integer of 2 or higher) from a leading end surface (22) side of a tool body (20) toward a base end surface (21) side, all of the angles (1 . . . m (where m is an integer of 2 or higher)) between lines connecting a rotational axis (O) and the cutting inserts (40) in the first segments of the respective spiral grooves (28) are different from each other, as viewed from the leading end surface side of the tool body (20), and an angle (t) between the cutting insert (40) in the first segment and the cutting insert (40) in the n.sup.th segment (the uppermost segment) in a spiral groove 28 is different from any of the angles 1 . . . m (where m is an integer of 2 or higher) between the lines, as viewed from the leading end surface side of the tool body (20).