Patent ID: 7226249

Claim:
A ball nose cutting insert, inserted into and attached to a groove-shaped insert-mounting seat formed on a distal end of a cutting tool body wherein the ball nose cutting insert is rotated about a longitudinal center axis of the cutting tool body, the ball nose cutting insert comprising: a roughly plate-shaped insert body; and a roughly circular cutting edge formed on a flank that is an outer peripheral surface of the plate-shaped insert body; wherein: the cutting edge is twisted at helix angles within a range of 5° to 25° with respect to the longitudinal center axis; the ball nose cutting insert has a thickness of between 0.5 D and 0.9 D where its flank intersects with a plane that is perpendicular to the longitudinal center axis and which passes through a ball center of the ball nose cutting insert, where D is the thickness of the plate-shaped insert body; mutually parallel flat surfaces formed on a pair of side faces of the insert body; grooves that open to flanks by being indented from the flat surfaces are provided in the edges of the pair of side faces on a side facing a front side in the direction of tool rotation in the insert mounted state; and walls in the grooves rising from bottom surfaces in the grooves toward the flat surfaces and intersecting at an obtuse angle relative to the bottom surfaces in the grooves.