Patent ID: 8870498

Claim:
A ball end mill including a ball end cutting edge ( 3 ) having a shape of an arc of approximately a quarter circle, wherein: a rake angle γ of each of portions of the ball end cutting edge ( 3 ) is set in a range from −10° to 0°, the negative value of the rake angle γ is increased from a tip of the ball end cutting edge ( 3 ) and a radially outer end ( 3 o ) of the ball end cutting edge ( 3 ) toward a middle point of the quarter circle, and is maximized at approximately a middle point of the quarter circle, the ball end cutting edge ( 3 ) has a convex shape in a tool rotation direction with respect to a line (L 1 ) connecting a rotation center (O) and the radially outer end ( 3 o ) of the ball end cutting edge in a front view of the tool, and the ball end cutting edge ( 3 ) has a rake face along the ball end cutting ( 3 ) having a convexly curved surface in a view along a direction vertical to a plane where the ball end cutting edge ( 3 ) appears as approximately a quarter circle.