Patent ID: 8585329

Claim:
A ball end mill wherein: a plurality of cutting edges are provided on a tip of the ball end mill having curvature; an inner circumference end of a rake face of each of the plurality of the cutting edges is arranged at a position offset forward in rotation direction from a spindle; the inner circumference end of the rake face of each of the plurality of the cutting edges is arranged at a position protruding oppositely to a side at which the cutting edge is formed from the spindle in radial direction for predetermined distance X 0 ; in each of the cutting edges, a part from an outer circumference end of a ridgeline, which is a boundary between the rake face and a flank of the cutting edge, to a midway of the ridgeline is determined as a main cutting edge; in each of the cutting edges, a part from the midway of the ridgeline to an inner circumference end of the ridgeline is determined as an auxiliary cutting edge; a connecting portion between the main cutting edge and the auxiliary cutting edge in each of the cutting edges is a portion protruding most toward the tip along the axial direction of the spindle; and wherein: 0<X 0 ≦W, and W is defined as the distance between a position on the ridgeline of each of the cutting edges where the distance from the spindle is smallest and the connecting portion of the cutting edge.