Milling cutter insert

An exchangeable milling insert for mounting in a cylindrical milling cutter tool and comprising a substantially square, planar base, a substantially square upper rake surface, side flanks extending outwardly from respective side edges of said base and intersecting said rake surface at respective cutting edges of said insert, each cutting edge comprising first, second and third successive portions wherein said first and third portions extend respectively from adjacent corners of said insert so as to merge with said second portion;

• said second portion constituting the major portion of the overall length of said cutting edge;
• said first portion sloping away from said base towards said second portion;
• said second portion sloping towards said base away from said first portion and towards said third portion and said third portion sloping away from said base away from said second portion and towards an adjacent corner of said insert;
• each side flank comprising upper and lower angularly disposed side surfaces of which the upper constitutes a relief flank surface and the lower constitutes a locating portion;
• at least the relief angle of said relief flank surface in the region of a leading end substantially equals the relief angle in the region of the trailing end, all when measured with respect to the tool;
• wherein during cutting, the first and second portions of a cutting edge cut an upright surface of a substantially 90.degree. recess in a workpiece with a third portion of an adjacent cutting edge serving as a wiper for a base surface of the recess, at least the first and second portions of each cutting edge being so located that all points thereon lie on a cylindrical envelope generated by a line parallel to a rotary axis of the cutting tool and rotating with respect to the rotary axis at a radius equal to the cutting radius of the cutting tool.