Ball end mill

A ball end mill comprising:

• an end mill body which is formed in a shaft shape;
• a plurality of convex arcuate end cutting edges which are disposed on a tip portion of the end mill body at intervals around an axis and form a hemispherical shape such that a rotational locus around the axis has a center on the axis;
• and
• a plurality of gashes which are respectively disposed to be adjacent to the plurality of end cutting edges in an end mill rotation direction around the axis,
• wherein the plurality of end cutting edges includes:
• a first end cutting edge of which a cutting edge length toward an inside in a radial direction orthogonal to the axis is longest among the plurality of end cutting edges,
• a second end cutting edge which is adjacent to the first end cutting edge in the end mill rotation direction and of which a cutting edge length toward the inside in the radial direction is shorter than that of the first end cutting edge, and
• a third end cutting edge which is adjacent to the second end cutting edge in the end mill rotation direction and of which a cutting edge length toward the inside in the radial direction is shorter than that of the second end cutting edge,
• wherein a depth of a gash of the second end cutting edge is deeper than that of a gash of the third end cutting edge,
• wherein a depth of a gash of the first end cutting edge is deeper than that of the gash of the second end cutting edge,
• a plurality of peripheral cutting edges which are disposed on an outer periphery of the end mill body at intervals around the axis, are respectively connected to radially outer end edges of the end cutting edges, and extend from the end edges toward a posterior end side of the end mill body,
• wherein, in a front view of the end mill body, the first end cutting edge extends from a connection portion between the peripheral cutting edge and the first end cutting edge toward the inside in the radial direction and a tip of the first end cutting edge in a cutting edge length is disposed at a position beyond the axis,
• wherein, in the front view of the end mill body, the second end cutting edge extends from a connection portion between the peripheral cutting edge and the second end cutting edge toward the inside in the radial direction and a tip of the second end cutting edge in a cutting edge length is disposed at a position which does not exceed the axis,
• wherein, in the front view of the end mill body, the third end cutting edge extends from a connection portion between the peripheral cutting edge and the third end cutting edge toward the inside in the radial direction and a tip of the third end cutting edge in a cutting edge length is disposed at a position which does not exceed the axis O, and
• the tip of the third end cutting edge is disposed an outside in the radial direction than the tip of the second end cutting edge.