SCREW HAVING UNDERSIDE CUTTERS AND POCKETS
A screw has a generally flat washer-like head. On an underside of the head are a plurality of cutters or cutting wedges arranged circumferentially around the shank of the screw. The cutters cut or carve off material when the screw is inserted into a fibrous material like wood to thereby facilitate countersinking of the screw head. The cutters may be triangular or quadrilateral wedges. One or more pockets are disposed radially inwardly of the cutters for receiving fibrous material to help lock the screw in place, i.e. to prevent the screw from loosening over time. These pockets may circularly shaped pockets disposed circumferentially around the shank. Alternatively, a single annular pocket may be provided around the shank.
1 . A screw comprising:
an elongated shank having a plurality of threads over at least a portion of the shank, the threads terminating in a tip at a first end of the shank;
a head disposed at a second end of the shank, the head having a substantially flat underside;
a plurality of cutters arranged circumferentially on the underside of the head, the cutters being adapted to facilitate countersinking of the head by cutting away material from a surface of a fibrous material into which the screw is being inserted; and
at least one pocket spaced radially apart from the cutters for receiving at least some of the fibrous material when the screw is inserted into the fibrous material.
2 . The screw as claimed in claim 1 wherein the at least one pocket comprises an annular groove formed radially inwardly of the cutters.
3 . The screw as claimed in claim 1 wherein the at least one pocket comprises a plurality of pockets disposed circumferentially around the shank and positioned radially inwardly of the cutters.
4 . The screw as claimed in claim 3 wherein a number of cutters exceeds a number of pockets.
5 . The screw as claimed in claim 4 wherein a ratio of cutters to pockets is 2:1.
6 . The screw as claimed in claim 5 comprising fourteen cutters and 7 pockets.
7 . The screw as claimed in claim 1 wherein the cutters are quadrilateral wedges.
8 . The screw as claimed in claim 1 wherein the cutters are triangular wedges.
9 . A method of fastening a screw to a piece of fibrous material, the method comprising:
positioning a tip of the screw against a surface of the fibrous material; and
applying torque to the screw to cause the screw to thread into the fibrous material until cutters on an underside of a head of the screw cut away some of the fibrous material from the surface to thereby facilitate countersinking of the head of the screw into the surface of the fibrous material, the torque being applied until some of the fibrous material enters one or more pockets formed in the underside of the head of the screw.
10 . The method as claimed in claim 9 wherein material enters an annular pocket formed in the underside of the head and disposed radially inwardly from the cutters.
11 . The method as claimed in claim 9 wherein material enters a plurality of pockets formed in the underside of the head and disposed radially inwardly from the cutters.
12 . A threaded fastener comprising:
a shank; and
a head at one end of the shank, the head having an underside in which are disposed a plurality of cutters for countersinking the head into a surface of fibrous material, the head further including at least one pocket disposed around the shank and disposed radially inwardly from the cutters to receive some of the fibrous material when the fastener is inserted.
13 . The fastener as claimed in claim 12 comprising a plurality of triangular wedge-shaped cutters.
14 . The fastener as claimed in claim 12 comprising a plurality of quadrilateral wedge-shaped cutters.
15 . The fastener as claimed in claim 12 comprising a single annular pocket disposed circumferentially around the shank.
16 . The fastener as claimed in claim 12 comprising a plurality of pockets disposed circumferentially around the shank.
17 . The fastener as claimed in claim 16 wherein a ratio of cutters to pockets is 2:1.
18 . The fastener as claimed in claim 16 comprising fourteen cutters and seven pockets.