End mill with conditioned cutting edge and method of making same

A rotary cutting tool, comprising:

• a shank portion;
• and
• a cutting portion extending from the shank portion to a cutting tip, the cutting portion having a plurality of blades separated by flutes, each of the blades including a relief surface and a radial cutting edge formed at an intersection between a respective flute and the relief surface,
• wherein the relief surface comprises an inner eccentric relief immediately adjacent the radial cutting edge and an outer eccentric relief immediately adjacent the inner eccentric relief,
• wherein the inner eccentric relief is formed with an inner eccentric relief angle, β, of less than about 5 degrees, and wherein the outer eccentric relief is formed with an outer eccentric relief angle, β, of between about 5 degrees and about 15 degrees, and
• wherein the inner eccentric relief is formed with a surface finish of less than 0.15 microns Ra.

A method of making a rotary cutting tool comprising a shank portion and a cutting portion, the cutting portion having a plurality of blades separated by flutes, each of the blades including a relief surface and a radial cutting edge formed at an intersection between a respective flute and the relief surface, the relief surface comprising an inner eccentric relief immediately adjacent the radial cutting edge and an outer eccentric relief immediately adjacent the inner eccentric relief, the method comprising:

• grinding a cylindrical blank to form a flute and a radial cutting edge by using a grinding wheel;
• grinding an outer relief surface behind and adjacent the radial cutting edge having an outer eccentric relief angle, β, of between about 5 degrees and about 15 degrees by using a grinding wheel;
• and
• grinding and polishing a portion of the outer eccentric relief surface immediately adjacent the radial cutting edge to form an inner relief surface having an inner eccentric relief angle, β, of less than about 5 degrees by using a fine grit grinding wheel.