Root-strength drill bit and method of making

A method for making a twist drill bit comprising;

• a. rotating a circularly symmetric drill blank about its own longitudinal axis,
• b. rotating a first, generally disc-shaped fluting grinding wheel about its own rotational axis, the plane of said fluting wheel being included at an angle A with respect to the longitudinal axis of said drill blank,
• c. moving said fluting wheel longitudinally into said blank at a linear speed of the proper relationship to the rotational speed of said blank about its own longitudinal axis so as to form helically disposed groove or flute in the cylindrical wall surface of said blank,
• d. repeating steps b and c a number of times equal to the number of additional flutes desired,
• e. rotating a second, generally disc-shaped, circular relieving grinding wheel about its own rotational axis, the plane of said relieving wheel being inclined at an angle B with respect to the longitudinal axis of said drill blank,
• f. engaging one of said flutes rearward from the front end of said flute with said relieving wheel, and moving said relieving wheel longitudinally into said blank at a linear speed of the proper relationship to the rotational speed of said blank about its own longitudinal axis so as to maintain a fixed circumferential relationship to said flute, said angle B being sufficiently smaller than angle A wherein the difference between the magnitudes of angle A and B is further defined as lying in the approximate range of 9 degrees to 17 degrees so as to reduce the diameter of all portions of said blank rearward of said forward end of flute, thereby forming a rearward directed cutting tooth at the junction of said forward end of said drill blank with said reduced diameter portion, and
• g. repeating step f on each desired additional flute.