Polygonal cutting insert

Claim 1

A polygonal indexable cutting insert comprising a pair of substantially parallel faces and peripheral side surfaces normal to said parallel faces, said faces and said side surfaces being joined to form corners, a pair of cutting edges extending away from each corner substantially within the plane of a respective one of said faces, a pair of floor surfaces, each floor surface being substantially parallel to a respective face and spaced downwardly therefrom, a ramp surface extending downwardly from a respective cutting edge to said floor surface whereby said insert has a positive rake, a backwall surface joining a respective floor surface and respective face surface and extending in a sinuous path from a position closely adjacent a respective corner inwardly and outwardly in a manner tending to deflect chips toward the center of said insert, said sinuous path comprising from three to five undulations, said backwall surface having a relatively shallow slope at the respective corners and a relatively steep slope intermediate said corners, said steep slope being at an angle of from about 30 to about 40 degrees and said shallow slope being at an angle of from about 5 to about 12 degrees, said sinuous path extends from a position closely adjacent a corner inwardly toward the center of the insert and outwardly toward the cutting edge, each undulation includes a curved portion near the center of the insert and a pair of outwardly extending leg portions successive legs being alternately longer and then shorter when progressing from a corner to the center of the insert in a direction parallel to the cutting edge.