Patent ID: 7478977

Claim:
A ball endmill comprising: a cylindrical tool body which is to be rotated about an axis thereof, and ball-nosed end cutting edges which are located in an axially distal end portion of said tool body and which describe a semi-spherical-shaped locus during rotation of said tool body, wherein each of said ball-nosed end cutting edges includes a first portion extending from said axis and provided by a radially inner portion of each of said ball-nosed end cutting edges, and a second portion contiguous to said first portion and provided by a radially outer portion of each of said ball-nosed end cutting edges, both the first portion and the second portion being located at a radially inner portion of the ball-nosed end cutting edge as seen in a distal end view, wherein said first portion is defined by a circular arc which is convex in a direction of the rotation of said tool body and which has a first radius of curvature in the distal end view, a ratio of said first radius of curvature to an outside diameter of said cylindrical body is in a range between 0.025 and 0.10, and wherein said second portion is defined by a circular arc which is convex in said direction of the rotation of said tool body and which has a second radius of curvature in the distal end view, said second radius of curvature is larger than said first radius of curvature.