Patent ID: 8434975

Claim:
A double-sided cutting insert for a cutting tool, comprising: a polygonal upper face having curved edges; a lower face having a rotationally symmetrical relation to the upper face; a plurality of flank faces for connecting one of the edges of the upper face to a corresponding edge of the lower face, respectively; a plurality of upper cutting edges, each of the upper cutting edges being formed on each of the edges of the upper face; a plurality of lower cutting edges, each of the lower cutting edges formed on each of the edges of the lower face; a plurality of upper chip-forming portions, each upper chip-forming portion having a rake face inclined toward a plane surface of the upper face from the upper cutting edge inwardly of the cutting insert and a plurality of protrusions arranged along an inner boundary of the rake face for deflecting chips; and a plurality of lower chip-forming portions, each lower chip-forming portion having a rake face inclined toward a plane surface of the lower face from the lower cutting edge inwardly of the cutting insert and a plurality of protrusions arranged along an inner boundary of the rake face for deflecting chips; wherein when the cutting insert is mounted to the cutting tool, a width of the rake face of the upper chip-forming portion adjacent to an edge portion forming a main cutting edge gradually increases in a direction going away from an axis of the cutting tool; and wherein a rake angle of the rake face of the upper chip-forming portion gradually increases from a narrower-width portion of the rake face toward a wider-width portion of the rake face.