Drill bit configuration
View Patent ↗This invention has to do with a rotary twist drill of the type having a fluted cylindrical shank with a drill bit end having at least two cutting edges extending radially outwardly from the longitudinal axis of the drill. Cutting edges are formed by the intersection of the flutes with the drill point end and extend radially outwardly from the center of the drill body to the outer perimeter of the drill body. Gashes formed on the drill point end form innermost cutting edge portions which are symmetrical with one another about a point offset both horizontally and vertically from the axial centerline of the drill body so as to allow a positive cutting action at the centerline of the material to be removed.
1. An elongate cylindrical drill body having a retainer shank on one end and a drill point on the other end and comprising:
a. At least two longitudinally extending flutes oppositely formed in the drill body and extending spirally along said drill body away from the retaining shank and through said drill point end;
b. Each flute when intersecting said drill point end forming a radially outward extending cutting edge with an adjacent chip guide surface;
c. Said radially extending cutting edges having a curved radially innermost cutting edge formed by a chip gash joining each flute with said cutting point end;
d. Said radially innermost part of said cutting edges and said gash configured to present a positive cutting rake angle to the material to be removed; and
e. The radially innermost cutting edges formed by the intersection of the gashes being symmetrical with one another about a point offset from the centerline of the drill body so as to allow a positive cutting rake action at the contact point of the material to be removed.
2. The drill body according to claim 1 in which the radius of curvature joining the innermost part of the cutting edge to the radially outermost extending part of the cutting edge is preferably configured to be from 10% to 16% of the diameter of the drill body.