Heavy duty cutting insert

Claim 1

An indexable throwaway insert formed of hard material for heavy duty cutting comprising a polygonal body having conjunctive sides lying in planes parallel to the axis of the body and defined by upper and lower peripheral edges lying in parallel planes perpendicular to said axis, each upper peripheral edge forming the outer boundary at a sharp junction of a narrow land extending inwardly and downwardly from the edge at a relatively low angle, a secondary surface extending around the periphery of said body joining conjunctively with the inner edge of said land and dropping sharply downward from said land at an angle of 30° to 55° and a central surface within said secondary surface in the form of a low angle, flat-sided pyramid rising from each side of the polygonal body substantially to but below the level of the plane of said edges at the center of the body, said central surface rising from the lowest point of the secondary surface in the direction of the center of the insert at an angle ranging from 1° to 5°.