All cutting edge drill

Claim 1

In an all cutting edge drill comprising: an elongated generally cylindrical body formed with a cone shaped end and chip clearance flutes in the side of and extending spirally about the cylindrical body, said body having an axis of rotation passing through the apex of the cone shaped end; the improvement in which said cone shaped end includes at least two circumferentially spaced end surfaces and the cylindrical body is formed with side surfaces extending from said end surfaces and directed spirally along the cylindrical body in circumferentially spaced relation to form chip clearance flutes; each of said end surfaces having margins adjacent said apex forming oppositely facing cutting edges starting at said axis of rotation to form a split drill-point, second cutting edges on said end surfaces forming continuations of said split point cutting edges and directed toward the sides of said cylindrical body and third cutting edges continuing from said second cutting edges and curving into said cylindrical body side surfaces; and said side surfaces having side cutting edges which are continuations of said third cutting edges and follow said spiral flutes, said third cutting edges having a radius of curvature of about 12 percent of the diameter of the cylindrical body and blending into said second cutting edges and said side cutting edges, whereby said drill in forming a hole cuts from said axis of rotation at said apex to and including the cylindrical sides of said body.