Ball end mill

A ball end mill comprising:

• an end mill main body rotated around an axis in an end mill rotation direction;
• and
• a hard coating film coated on at least a surface of a distal end portion of the end mill main body, wherein
• two chip discharge grooves opening to distal end flank faces of the end mill main body and extending to a rear end side are formed on an outer circumference of the distal end portion of the end mill main body to be rotationally symmetrical with respect to the axis,
• a bottom blade having a convex hemispherical shape whose rotation trajectory around the axis has a center on the axis is formed on each of intersecting ridge line portions between wall surfaces of the two chip discharge grooves facing the end mill rotation direction and the distal end flank faces,
• a diameter D (mm) of a convex hemisphere formed by the bottom blade in the rotation trajectory around the axis is 2 mm or less,
• the chip discharge grooves face each other on opposite sides with the axis interposed therebetween without overlapping each other when viewed from a distal end side in the axial direction, a ratio W/D of a width W (mm) of a chisel portion left between the facing chip discharge grooves to the diameter D (mm) is within a range of 0.020 to 0.060, and a ratio L/D of a facing length L (mm) of the chip discharge grooves to the diameter D (mm) is within a range of 0.014 to 0.090, and
• a rake angle of the bottom blade in a range in which a chisel edge is formed in the chisel portion is within a range of −15° to −30°.