Drill bit for hand drills

A drill bit for hand drills, said bit having a drill shank and a clamping shank which has a longitudinal axis and a circumferential surface, said circumferential surface being interrupted by at least two angularly spaced and generally longitudinally extending grooves, each of said grooves being symmetrical about a geometric plane which includes said longitudinal axis, said circumferential surface having at least one formation which adjoins each of said grooves, said at least one formation for each groove being a surface which is cylindrical about an axis which is parallel to and eccentrically offset from said longitudinal axis and which is in the geometric plane of symmetry of the involved groove.

A drill bit of metal for hand drills, said bit having a drill shank and a clamping shank which has a longitudinal axis and a generally circumferential surface which is characterized by displaced-metal formations, said circumferential surface being interrupted by at least two angularly spaced and generally longitudinally extending indented groove formations, said circumferential surface having at least one outwardly displaced formation which adjoins each of said grooves, said formations being surfaces which are other than cylindrical about said longitudinal axis, and at least one of said grooves terminating of the clamping shank end of said drill bit.

A set of drill bits of different thickness, wherein each bit has a drill shank and a clamping shank which has a longitudinal axis and a circumferential surface, and wherein the circumferential surface of one drill bit is larger than the circumferential surface of another drill bit, the circumferential surface of each drill bit being interrupted by at least two angularly spaced and generally longitudinally extending grooves, each of said grooves being symmetrical about a geometric plane which includes said longitudinal axis, each of said circumferential surfaces having at least one formation which adjoins each of said grooves, said at least one formation for each groove being a surface that is cylindrical about an axis (a) which is parallel to and eccentrically offset from the longitudinal axis of the involved drill bit and (b) which is in the geometric plane of symmetry of the involved groove, the radius of all said cylindrical formation surfaces being the same.

A set of hand-drill bits of metal of different thickness, wherein each drill bit has a drill shank and a clamping shank which has a longitudinal axis and a generally circumferential surface which is characterized by displaced metal formations, and wherein the circumferential surface of one drill bit is larger than the circumferential surface of another drill bit, the circumferential surface of each drill bit being interrupted by at least two angularly spaced and generally longitudinally extending indented groove formations, each of said circumferential surfaces having outwardly displaced formations which adjoin each of said grooves, said formations for each groove being surfaces other than cylindrical about said longitudinal axis, the sectional profile of each groove and its associated formation surfaces being identical for all drill bits of said set, and at least one of said grooves of each drill bit terminating short of the clamping-shank end of the involved drill bit.