Chip breaker drill screw

Claim 1

A drilling and thread cutting screw comprising a threaded shank, driving tool accommodating means integral with a trailing end of the shank and including a forged drilling portion at the leading end thereof, the drilling portion including first and second oppositely disposed flute means extending generally longitudinally of the shank, outwardly and axially rearwardly flaring entering end surfaces being located between the flute means, each flute means defined by a substantially concave surface intersecting the drilling portion and forming cutting edges and drag edges associated with each flute, the cutting edges associated with each flute including a first cutting edge portion extending outwardly and rearwardly from the extremity of the entering end and a second cutting edge portion, which is an extension of the first cutting edge portion and which extends generally longitudinally of the screw a distance defined by the length of the associated flute means, the concave surface of each flute including at least one discrete obstruction formed thereon adjacent to but sightly inward of each of the first and second cutting edge portions, the discrete obstruction being forged in the flute when the drilling portion is forged, said obstruction being a surface generally oblong in shape with its longest dimension essentially extending transverse of the flute, the surface of the obstruction being a surface of revolution of an ellipse which intersects with the generally concave surface of the flute, thereby providing an impediment to the normal free flow of curling chips serving to break these curling chips into relatively small lengths without impairing the drilling and thread cutting ability of the screw.