Patent ID: 7524148

Claim:
An indexable insert prepared by bonding a superhard sintered body containing cubic boron nitride to at least the upper surface of an apical angle part of a tool body having a polygonal shape in top view and forming an edge and a chip breaker on said superhard sintered body, wherein a chamfer is formed on the intersection between the upper surface and the side surface of said superhard sintered body, said chip breaker has a substantially symmetrical shape with respect to a section bisecting the apical angle of said apical angle part, and has a protrusion and a flat part provided between said protrusion and said apical angle part, a pair of ridges reaching said chamfer, the pair of ridges are on the apex of said protrusion and are linear or arcuate, θ is in the range of 6/10×α≦θ≦90−1/10×α assuming that θ represents an angle formed by the linear ridges of said protrusion or a tangential line for said arcuate ridges at a point bisecting the arcuate ridges of said protrusion and a bisector for said apical angle and α represents said apical angle, and a line segmental ratio is in the range of 0.9≦L 1 ′/L 1 ≦1.1 assuming that L 1 represents the length of a line segment connecting a first intersection between said pair of ridges on the apex of said protrusion and an extreme point of first said ridge and L 1 ′ represents the length of a line segment connecting an extreme point of second said ridge and said first intersection, and 0.2≦L 1 /L 2 0.8 assuming that L 2 represents the length of a line segment connecting a second intersection between a straight line passing through the extreme point of said first ridge from said first intersection and the outer periphery of said tool body and said first intersection.