An indexable cutting insert comprises an upper surface, a bottom surface and side surface extending between said two surfaces. Between two adjacent cutting corners, a rake surfaces is formed such that the rake angle decreases with increasing cutting depth. In this way the cutting edge is reinforced towards a maximal cutting depth. This configuration is favorable, for example, at the machining of materials with a tendency of surface hardening.

A cutting insert for use in a peripheral rotary milling cutter having a cylindrical holder and a plurality of replaceable, peripherally disposed cutting inserts, the cutting insert being formed with at least one cutting edge defined between a cutting rake surface and a relief flank surface of the insert. The cutting edge is curved and forms part of the curved side of a plane which intersects a cylinder constituting a surface of revolution of said cutting edge at an angle corresponding to the axial rake angle of the insert in the milling cutter.

A cutting insert for use in a peripheral rotary milling cutter having a cylindrical holder and a side cutting edge defined between a cutting rake surface and a side relief flank and a side base edge defined between the side relief flank and a base surface. The side relief flank has first and second component side relief flank surfaces which intersecet at an intersection line, the latter extending along the side relief flank from a first position adjacent a leading end of the insert and located at an intermediate position thereof to a second position intersecting the cutting edge and adjacent a trailing end of the insert. The component flank surfaces are substantially planar and are angularly disposed with respect to one another so that an insert side relief angle (.gamma..sub.A) as defined with respect to the cylindrical holder in the region of the leading end substantially equals an insert side relief angle (.gamma..sub.B) in the region of the trailing end.

A cutting insert for use in a peripheral rotary milling cutter having a cylindrical holder and at least one replaceable, peripherally disposed cutting inserts, the cutting insert being formed with at least one cutting edge defined between a cutting rake surface and a relief flank surface of the insert. The cutting rake and relief flank surfaces are continuously curved so that the insert rake and relief angles as defined with respect to the cylindrical holder remain substantially invariant along the length of the cutting edge.

A cutting insert for a rotary routing cutter tool, the insert being of substantially parallelepipedal shape and having a first pair of elongated cutting edges substantially parallel to a rotary axis of the insert, each cutting edge of the first pair being defined between contiguous rake and relief surfaces of the insert; a second pair of cutting edges transversely directed with respect to the first pair, each cutting edge of the second pair comprising first and second successive cutting portions, the first cutting edge portion merging with an adjacent cutting edge of the first pair via a rounded insert corner, the adjacent cutting edges defining at the corner a substantially acute angle; the second cutting edge portion sloping towards a base of the insert so as substantially to intersect the rotary axis and so as to merge with an adjacent cutting edge of the first pair via a coupling portion which slopes away from the insert base.