Drill tip and fastener employing same

Claim 1

A drill device comprising: (a) a shaft having a driving end adapted to be rotationally driven to rotate said shaft about its longitudinal axis; (b) a drill tip formed on said shaft, comprising (1) an initial work-piece contacting end portion which is displaced to one side of said axis; (2) a back-relieved primary cutting edge defined by a first slot in said drill tip and extending obliquely outwardly from said end portion on said one side of said axis and at a predetermined first angle with respect to said axis, so as to provide initial eccentric drilling of the work-piece by said primary cutting edge; (3) a back-relieved secondary cutting edge defined by a second slot in said drill tip and extending obliquely outwardly at a predetermined second angle with respect to said axis and opposite said primary cutting edge with respect to said axis, so as to assist said primary cutting edge in drilling said work-piece after drilling has been started by said primary cutting edge; and (c) a conical portion symmetrical with respect to said axis and diverging in the direction toward said driving end at a third angle to said axis smaller than said first and second angles, said conical portion extending from the portion of said drill tip containing said primary and secondary cutting edges to the diameter of said shaft, whereby said conical portion serves to enlarge the opening made in said work-piece by said primary and secondary cutting edges as said device is rotated and forced further into said opening.