An indexable cutting insert (10) for a tool (18) adapted to cut internal right-angled corners in a work piece (19). The insert (10) has a square configuration and comprises a top major surface (11), a bottom major surface (12) and connecting side surfaces (13). The lines of junction between the top major surface and the side surfaces define the main cutting edges (14) and the minor cutting edges (15). The main cutting edges (14) transite into the second cutting edges (15) in the corners of the insert. Each second cutting edge (15D) projects from the square basical shape so that it will lift the inactive main cutting edge (14A) from the machined surface under the insert.

A cutter insert of the indexable type for a rotary cutter includes a body of a plate of a generally circular shape and having three notches of a V-shape formed in a circumferential face of the body in equally circumferentially spaced relation, each V-shaped notch being defined by a pair of first and second opposed walls. A front face of the body cooperates with the circumferential face, interrupted by the three V-shaped notches, to define three arcuate convex cutting edges each having a leading and a trialing end. A marginal portion of the front face disposed adjacent to and extending along each cutting edge serves as a rake surface for the cutting edge, the rake surface being recessed adjacent to the first wall of the V-shaped notch so as to slope toward a rear face of the body toward the first wall to provide a convex portion extending between the front face and the first wall. The first wall of each V-shaped notch, intersecting a respective one of the cutting edges at the leading edge thereof, is sloping toward the trailing end of the adjacent cutting edge at the second wall of the notch and is inclined with respect to a plane disposed perpendicular to the front face and passing through a center of a circle along which the one cutting edge extends and the leading end of the one cutting edge disposed at the first wall.

A throwaway insert having a generally quadrilateral-shaped flat plate configuration is disclosed that includes first and second major faces disposed parallel and opposite to each other; oppositely facing first and second side faces extending between the first major face and the second major face; remaining oppositely facing third and fourth side faces extending between the first major face and the second major face; major cutting edges, one each constituted along each of the intersections of the first and second major faces with the first and second side faces minor flanks, one each constituted along the intersections of each of the first and second major faces with the third and fourth side faces, the minor flanks extending between a pair of oppositely formed intersections of the first major face with the first and second side faces, and between a pair of the oppositely formed intersections of the second major face with the first and second side faces, where the intersection constitutes the major cutting edge; and minor cutting edges respectively constituted along the intersection of one end of the minor flanks with either of the first and second side faces. The minor flanks include a transition portion so as to form a multi-stage face of concave cross section including at least two face elements.

An insert rotary cutter for processing a metal workpiece includes a cutter body having an axis of rotation therethrough. The cutter includes at least one cutter insert releasably mounted on an outer periphery of the body. The insert is of a generally polygonal shape having a curved front face. The front face has a pair of opposed marginal ridges serving as respective main cutting edges. The front face has marginal portions disposed adjacent and extending along the main cutting edges, and the marginal portions serve as respective rake surfaces for the main cutting edges. Each of the rake surface is convexly curved as viewed from a respective one of the main cutting edges and is concavely curved as viewed along a respective one of the main cutting edges.

An end mill comprises an end mill body and a throw-away tip mounted on a forward end of the end mill body so as to be spaced from an axis thereof. A core receiving recess is formed at a center of a forward end face of the end mill body and has a size equal to or greater than a distance between the throw-away tip and the axis of the end mill body. The throw-away tip has an end cutting edge formed by a cutting edge ridge located adjacent the forward end of the end mill body and extending from an outer peripheral side of the end mill body toward an inner peripheral side thereof, and outer and inner peripheral cutting edges respectively formed by cutting edge ridges respectively extending from outer and inner peripheral ends of the end cutting edge toward a rearward end of the end mill body. The end mill body may mount at least two throw-away tips disposed symmetrically with respect to the axis thereof.