Patent ID: 7789597

Claim:
A method of reducing chatter in a rotary cutting tool comprising: providing an end mill including a body having a cutting portion and a shank portion; a plurality of diametrically-opposed helical flutes formed in the cutting portion of the body, where adjacent helical flutes form an index angle therebetween in each radial plane along the axial length of the flutes; and a plurality of peripheral cutting edges formed along an intersection of a circumferential surface of the cutting portion of the body and a portion of an inner surface of a respective one of the helical flutes facing in a direction of rotation of the body, each peripheral cutting edge having a radial rake angle; forming the index angle between a first pair of adjacent helical flutes different from the index angle between an other pair of adjacent helical flutes in at least one of the radial planes, where the index angles are non-ninety degree angles; and forming the radial rake angle of one peripheral cutting edge of a first helical flute different from the radial rake angle of another peripheral cutting edge of an adjacent helical flute, where one of the radial rake angles is at least seven degrees positive and the other radial rake angle is at least three degrees less than the one other.