Self-countersinking screw with cutting receiving pockets

Abstract

A self-countersinking screw including an inverted-conical head portion formed at a top with a cavity adapted to receive a tip of a screwdriver and having a conical bottom, said conical bottom having a plurality of triangular recesses each having a lateral side extending inwardly to form a sharp edge and a space for receiving chips, a threaded portion, and a tapered portion having a large diameter connected with the head portion and a small diameter connected with the threaded portion, whereby the sharp edge will make a countersink on a workpiece when the countersunk head screw is turned therein.

Description

Matter enclosed in square brackets between upper ends of the trailing wall 16 and of the leading boundary 17 in a circumferential direction and is generally parallel with the top of the head 11. Thus, the wall 22 appears linear in a side view (FIG. 2). The walls 22 of all recesses 15 are coplanar with one another as can be seen from FIG. 1 and are perpendicular to the axis 21 of the screw.

FIG. 4 shows the radial width of the upper boundary wall 22, merges with the obtuse angled edge of the leading boundary 17, and has a zero width there. On the contrary, at the trailing wall 16, the radial width of the boundary wall 22 is higher due to the inclination of the bottom wall 19. Thus, it can be seen that the bottom wall 19 slopes into the respective cutout 15 from the leading boundary 17 to the corner between the trailing wall 16 and the boundary wall 22. This, together with the widening of the recess 15 in the outward direction, is the preferred way of providing an increase in the volume of each cutout in the direction along the underside 14 and away from the axis 21. The depth of the recess 15 is at a maximum at the corner of the walls 22 and 16.

A tapered intermediate portion 23 is formed between the head 11 and the threaded stem 12. It includes a large diameter section 24 merging with the head 11 and small diameter section 25 merging with the threaded portion 12.

In operation, (FIGS. 5 and 6), the screw is threaded into a workpiece 26 which is typically made of wood laminated with a Melamine™ or the like surface finish sheet. The intermediate portion has a small included angle of the frustoconical face. Thus, when the screw is driven into a workpiece, the frustoconical face is drawn into a passage previously made by the stem of the screw. Eventually, the underside 14 having a relatively large included angle, reaches the surface of the workpiece and as it is pressed against the bore left after the cutting edges 18 of the recesses 15, cut or burr a conical countersink in the workpiece. Since the cutting edges 18 are coincident with the frustoconical surface of the underside, the countersink corresponds exactly to the taper of the underside thus providing a firm and accurate engagement between the head of the screw and the countersink in the workpiece. The plurality of co-planar upper boundary walls 22 further reinforces the firm hold of the screw in the workpiece by blocking axial displacement of the screw beyond a certain limit. The gradually increasing depth of the recesses 15 accommodates chips developed by the countersinking thus permitting firm engagement of the underside surface 14 with the countersink. The overall structure of the head is simpler than in known prior art and is thus less expensive to produce.

Those skilled in the art will readily appreciate that many modifications may exist of the preferred embodiment described without departing from the scope of the present invention. The upper part of the underside of the head may be modified to provide an outwardly projecting flange. The cutting edge may be curved even though a straight edge is preferred from the standpoint of manufacturing costs. The leading boundary 17, instead of being an obtuse angled joinder, may have the shape of an edge of a leading wall. These are but a few of examples of many modifications within the scope of the present invention.

Therefore, I wish to protect by Letters Patent which may issue on this application all such embodiments as fairly fall within the scope of my contribution to the art.

Claims

1. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising a thread adapted to drive the screw into a workpiece when the threaded stem portion is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, said recesses having straight sides, each said recess being axially spaced from said stem and from said top face;

(d) each recess comprising from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(e) each said recess further including:

(i) a leading wall which is generally planer and convergent with said trailing wall in the direction along said underside and towards the axis of the screw;

(ii) a generally planer upper boundary wall extending between upper ends of said trailing wall and said leading wall in a circumferential direction and disposed at a spacing from said top along said frusto-conical surface; and

(iii) a flat, generally triangular bottom.

2. The screw of claim 1 8, further comprising a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion.

3. The screw as claimed in claim 1 8, wherein the upper boundary walls are all generally coplanar with a single plane which is generally perpendicular to the axis of the screw and is spaced from said top surface.

4. The screw as claimed in claim 1 8 wherein the depth of each said recess increases in the direction from said leading wall boundary to a corner between said trailing wall and said upper boundary wall.

5. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem and from said top face;

(d) a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including:

(i) from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading wall which is generally planar and convergent with said trailing wall in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between upper ends of said trailing wall and said leading wall in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom.

6. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem is rotated about its axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem portion and from said top face;

(d) a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including;

(i) from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading wall which is generally planar and convergent with said trailing wall in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between upper ends of said trailing wall and said leading wall in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom;

(f) the upper boundary walls of each said recesses being all generally coplanar with a single plane generally perpendicular to the axis of the screw and spaced from said top surface.

7. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem portion and from said top face, the depth of each said recess increasing in the direction from a leading wall to a corner between a trailing wall and said upper boundary wall;

(d) each said recess having a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including:

(i) from the standpoint of said predetermined direction, generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading wall which is generally planar and convergent with said trailing wall in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between upper ends of said trailing wall and said leading wall in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom so arranged that the depth of each said recess increases in the direction from said leading wall to a corner between said trailing wall and said upper boundary wall;

(f) the upper boundary walls of each said recesses being all generally coplanar with a single plane generally perpendicular to the axis of the screw and spaced from said top surface.

8. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising a thread adapted to drive the screw into a workpiece when the threaded stem portion is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, said recesses having straight sides, each said recess being axially spaced from said stem and from said top face;

(d) each recess comprising from the standpoint of said predetermined direction, a generally planar trailing wall forming a cutting edge coincident with said frusto-conical underside;

(e) each said recess further including:

(i) a leading boundary which is convergent with said cutting edge in the direction along said underside and towards the axis of the screw;

(ii) a generally planar upper boundary wall extending between an upper end of said trailing wall and an upper end of said leading boundary in a circumferential direction and disposed at a spacing from said top along said frusto-conical surface; and

(iii) a flat, generally triangular bottom.

9. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem and from said top face;

(d) a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including:

(i) from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading boundary which is convergent with said cutting edge in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between an upper end of said trailing wall and an upper end of said leading boundary in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom.

10. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem portion is rotated about its axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem portion and from said top face;

(d) a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including:

(i) from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading boundary which is convergent with said cutting edge in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between an upper end of said trailing wall and an upper end of said leading boundary in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom:

(f) the upper boundary walls of each said recesses being all generally coplanar with a single plane generally perpendicular to the axis of the screw and spaced from said top surface.

11. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising thread adapted to drive the screw into a workpiece when the threaded stem is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, each said recess being axially spaced from said stem portion and from said top face;

(d) each said recess having a tapered intermediate portion tapering in a direction away from the head and disposed between said underside and said stem portion, said intermediate portion including a large diameter section adjoining said underside, and a small diameter section adjoining said threaded stem portion;

(e) each said recess including:

(i) from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(ii) a leading boundary which is convergent with said cutting edge in the direction along said underside and towards the axis of the screw;

(iii) a generally planar upper boundary wall extending between an upper end of said trailing wall and said leading boundary in a circumferential direction and disposed at an axial spacing from said top along said frusto-conical surface; and

(iv) a flat, generally triangular bottom so arranged that the depth of said recess increases in the direction from said leading boundary to a corner between said trailing wall and said upper boundary wall;

(f) the upper boundary walls of each said recesses being all generally coplanar with a single plane generally perpendicular to the axis of the screw and spaced from said top surface. 12. A self-countersinking screw having a body with a longitudinal axis, said body comprising in combination:

(a) a head which includes screwdriver engaging means at a top face and an underside having an inversely frusto-conical surface;

(b) a threaded stem portion integral with the head and comprising a thread adapted to drive the screw into a workpiece when the threaded stem portion is rotated about said axis in a predetermined direction;

(c) a plurality of generally triangular recesses on said underside, said recesses having straight sides, each said recess being axially spaced from said stem and from said top face;

(d) each recess comprising from the standpoint of said predetermined direction, a generally planar trailing wall forming a linear cutting edge coincident with said frusto-conical underside;

(e) each said recess further including:

(i) a leading boundary which is convergent with said cutting edge in the direction along said underside and towards the axis of the screw;

(ii) a generally planar upper boundary wall extending between an upper end of said trailing wall and an upper end of said leading boundary in a circumferential direction and disposed at a spacing from said top along said frusto-conical surface; and

(iii) a flat, generally triangular bottom.