Rotary cutting tool

In an improved rotary cutting tool comprising a body having a cutting part and an axis of rotation therethrough, said body having an even number of helical flutes formed in a circumferential surface of the cutting part in circumferentially spaced relation to one another and extending helically axially of the cutting part so as to define an even number of helical lands of a generally uniform land width spaced circumferentially of the cutting part from one another, said body having an even number of helical peripheral cutting edges each defined by a portion of an inner surface of a respective one of the helical flutes facing in a direction of rotation of the body and a surface of the land adjacent to said portion of the inner surface, at least one of said peripheral cutting edges having a helix angle different from helix angles of the other peripheral cutting edges, the improvement comprising:

• the even number of peripheral cutting edges being equally spaced circumferentially of the body in at least one plane disposed perpendicular to the axis of rotation of the body, the even number of peripheral cutting edges being comprised of a plurality of pairs of diametrically opposite cutting edges, the two peripheral cutting edges of each of said pairs of cutting edges having the same helix angle and thereby being symmetrical with respect to the axis of the body, and
• said even number of peripheral cutting edges includes a plurality of pairs of adjacent peripheral cutting edges, a first cutting edge of each of said pairs of adjacent cutting edges having a uniform helix angle along the entire length of said first cutting edge, a second cutting edge of each of said pairs of adjacent cutting edges including a forward portion having a forward helix angle and a rearward portion having a rearward helix angle different than the forward helix angle of said second cutting edge.

In an improved rotary cutting tool comprising a body having a cutting part and an axis of rotation therethrough, said body having an even number of helical flutes formed in a circumferential surface of the cutting part in circumferentially spaced relation to one another and extending helically axially of the cutting part so as to define an even number of helical lands of a generally uniform land width spaced circumferentially of the cutting part from one another, said body having an even number of helical peripheral cutting edges each defined by a portion of an inner surface of a respective one of the helical flutes facing in a direction of rotation of the body and a surface of the land adjacent to said portion of the inner surface, at least one of said peripheral cutting edges having a helix angle different from helix angles of the other peripheral cutting edges, the improvement comprising:

• the even number of peripheral cutting edges being equally spaced circumferentially of the body in at least one plane disposed perpendicular to the axis of rotation of the body, the even number of peripheral cutting edges being comprised of a plurality of pairs of diametrically opposite cutting edges, the two peripheral cutting edges of each of said pairs of cutting edges having the same helix angle and thereby being symmetrical with respect to the axis of the body, and each of said peripheral cutting edges including (i) a helical cutting edge portion with said helix angle of the cutting edge and (ii) a short cutting edge portion at a forward end thereof having a positive axial rake angle smaller than the helix angle of the cutting edge.

In an improved rotary cutting tool comprising a body having a cutting part and an axis of rotation therethrough, said body having an even number of helical flutes formed in a circumferential surface of the cutting part in circumferentially spaced relation to one another and extending helically axially of the cutting part so as to define an even number of helical lands of a generally uniform land width spaced circumferentially of the cutting part from one another, said body having an even number of helical peripheral cutting edges each defined by a portion of an inner surface of a respective one of the helical flutes facing in a direction of rotation of the body and a surface of the land adjacent to said portion of the inner surface, at least one of said peripheral cutting edges having a helix angle different from helix angles of the other peripheral cutting edges, the improvement comprising:

• the even number of peripheral cutting edges being equally spaced circumferentially of the body in at least one plane disposed perpendicular to the axis of rotation of the body, the even number of peripheral cutting edges being comprised of a plurality of pairs of diametrically opposite cutting edges, the two peripheral cutting edges of each of said pairs of cutting edges having the same helix angle and thereby being symmetrical with respect to the axis of the body, and
• each flute having a uniform radial depth over substantially the entire axial length of the flute.