Self-counter-sinking screw with circumferential cutters
A self-countersinking screw ( 10 ) is capable of full penetration into wood, plastic veneered wood, and cementaceous products. An alternating sequence of peripheral cutters (A, B) extend from the periphery of the underside of the screw head ( 11 ), acting in conjunction with countersink cutting edges ( 24 ) and debris receiving recesses ( 20 ). Cutter (A) has an arcuate notch ( 30 ) in the cutting face ( 28 ), cutter (B) has a rectangular notch ( 31 ) in the trailing edge. Full countersinking without tearing, cracking or dimpling of the surface is achieved.
1. A self-countersinking screw comprising:
a threaded shank having a longitudinal axis,
a screw head including driver engageable means on a top surface; and an underside having a frustoconical shoulder tapering to the threaded shank;
the frustoconical shoulder having a plurality of generally triangular recesses therein, whereby the recesses have a generally vertical wall substantially in a plane parallel to the axis of the screw,
the underside of the head having a plurality of pairs of cutters arranged peripherally around the circumference and abutting each triangular recess;
the cutters comprising a succession of two cutter shapes, a first cutter having a first generally scalene triangular shape adjoining the vertical wall of the triangular recess and a second cutter having a second generally scalene triangular shape different from the first generally scalene triangular shape and being incorporated into the triangular recess.
2. The screw of claim 1 , wherein both cutters have a steep leading cutting face in the direction of rotation of the screw, and a trailing surface intersecting the leading face at a crest which provides a cutting edge;
the triangular first cutter being bifurcated at its crest to provide two cutting edges; and
the triangular second cutter having a notch extending laterally inwardly from the circumference of the trailing surface of the second cutter.
3. The screw of claim 2 , wherein the crest of the first cutter is bifurcated by an arcuate notch extending laterally inwardly.
4. The screw of claim 3 , wherein the arc of the notch has a radius no greater than the width of cutters.
5. The screw of claim 2 , wherein the notch of the second cutter is generally rectangular, with the length extending parallel to the periphery of the screw head.
6. The screw of claim 5 , wherein the generally rectangular notch provides a secondary cutting face at its trailing end.
7. The screw of claim 6 , wherein the generally rectangular notch has an interface inclined inwardly towards the axis of the screw.
8. The screw of claim 1 , wherein the frustoconical shoulder has a first frustoconical portion adjacent the shank and a second frustoconical portion between the first frustoconical portion and the underside of the head.
9. The screw of claim 1 , wherein the first frustoconical portion has a smaller included angle than the included angle of the second frustoconical portion.
10. The screw of claim 1 , wherein the triangular recesses are in the second frustoconical portion.
11. A self-countersinking screw comprising:
a threaded shank having a longitudinal axis,
a screw head including driver engageable means on a top surface; and an underside having a frustoconical shoulder tapering to the threaded shank;
the frustoconical shoulder having a plurality of generally triangular recesses therein, whereby the recesses have a generally vertical wall substantially in a plane parallel to the axis of the screw, the periphery of the underside of the head having a plurality of cutters arranged circumferentially and abutting the frustoconical shoulder and recesses;
the cutters comprising a succession of two cutter shapes, a first cutter having a first generally scalene triangular shape adjoining the vertical wall of the triangular recess and a second cutter having a second generally scalene triangular shape being incorporated into the triangular recess,
wherein both cutters have a steep leading cutting face in the direction of rotation of the screw, and a trailing surface intersecting the leading face at a crest which provides a cutting edge;
the triangular first cutter being bifurcated at its crest to provide two cutting edges; and
the triangular second cutter having a notch extending laterally inwardly from the circumference of the trailing surface of the second cutter.