Patent ID: 8876441

Claim:
A cutting insert formed of a plate-like member with a substantially polygonal outer shape and comprising: a rake face with a chip breaker which is formed on at least one of top and bottom surfaces; a flank formed on an outer peripheral surface extending between the top and bottom surfaces; and a cutting edge formed on an intersection portion between the rake face and flank, the cutting edge comprising: an arc-shaped cutting edge being curved in an arc shape and located on at least one nose portion of the cutting insert, a working cutting edge extending from one side of the arc-shaped cutting edge, and a linear cutting edge extending from the other side of the arc-shaped cutting edge, wherein a chip-breaker concave portion is formed in the vicinity of the arc-shaped cutting edge on the rake face; a breaker projection stands from a bottom surface portion of the chip-breaker concave portion; and the chip-breaker concave portion is defined by an inclined surface which is curved in a concave manner and which is smoothly connected to the bottom surface portion while being gradually inclined toward the bottom surface portion, from a peripheral nose edge portion on the nose portion side to the bottom surface portion.