Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Head having counter-sinking means
Reexamination Certificate
2000-08-09
2001-10-16
Saether, Flemming (Department: 3627)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Head having counter-sinking means
Reexamination Certificate
active
06302631
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a wood screw.
Wood screws comprise a threaded shank with a pointed tip at one end thereof and a head at the other end. The head has a recess for accepting a screwdriver tip.
Most wood screws have a conical head. Thus, when a wood screw is driven and the conical head begins to penetrate into a wooden plate, the turning resistance increases suddenly due to large friction. Therefore, a large turning torque is needed to drive the screw completely.
A power screwdriver or a torque wrench with a built-in torque limiter is often used to drive a wood screw into a wooden plate. In such a case, since the turning torque increases suddenly and sharply when the conical head begins to penetrate into the plate, the torque limiter may activate to stop the transmission of turning torque before the head is fully buried in the plate. If this happens, it is impossible to completely drive the screw into the plate. The screw head would remain above the plate surface.
When the conical head begins to penetrate into the plate, it is jammed into the narrow hole formed by the threads on the shank and acts like a wedge. Thus, even if the head is completely buried in the plate, the wooden plate tends to be cracked.
An object of the invention is to provide a wood screw that can be completely driven into a wooden plate with a small turning torque without forming a crack in the wooden plate.
SUMMARY OF THE INVENTION
According to the invention, there is provided a wood screw comprising a shank having a pointed tip at one end and formed with threads, and a head provided at another end of said shank, said head being in the shape of a pyramid having side ridges defining side faces therebetween and having a top surface formed with a recess for accepting a tip of a screw driving tool.
The side faces of the pyramid head defined by the ridges may be flat or arcuately convex or concave in the axial direction of the screw or in the direction perpendicular to the axial direction.
When the pyramid head penetrates into the plate while rotating, the ridges of the pyramid head cut and ream the hole formed by the threads on the shank like drill edges. The head thus sinks smoothly into the plate. Also, the wooden plate is less likely to be cracked.
A rake face may be formed along and in front of each ridge with respect to the rotational direction of the screw when driven into the wooden plate to sharpen the ridges. The thus sharpened ridges will ream the hole formed by the threads on the shank more smoothly, so that the screw can be completely and easily driven into even an extremely hard wooden plate. Also, such sharp ridges can effectively prevent fibrous chips of the plate from heaping along the edge of the opening formed by the ridges because the ridges cut fibers into smaller pieces.
The greater the number of corners or ridges of a polygonal pyramid head, the closer in shape the polygonal pyramid is to a cone, and the greater the angle of each corner or ridge. A corner or ridge having a large angle is correspondingly “dull” as a drill edge. Thus, to provide sufficiently sharp drill edges, the number of corners of the polygonal pyramid head has to be sufficiently small. The practically preferable number of corners of the pyramid head is between four (square pyramid) and six (hexagonal pyramid).
The pyramid head may be formed with a square recess in its top face to receive the tip of a screw driving tool. If the pyramid head is a square one, a cross-shaped recess for accepting a screwdriver tip may be formed in its top surface so that its four grooves extend toward the respective four ridges with their bottoms tapered at the same angle as the ridges to form a deep recess. Since the recess is deep, the screwdriver can strongly engage the wood screw.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:
REFERENCES:
patent: 373074 (1887-11-01), Jones
patent: 4655661 (1987-04-01), Brandt
patent: 5015134 (1991-05-01), Gotoh
patent: 1036978 (1953-09-01), None
patent: 140983 (1920-04-01), None
patent: 2227540 (1990-08-01), None
Kashikura Tsutomu
Takasaki Seiichiro
Saether Flemming
Takasaki Seiichiro
Wenderoth , Lind & Ponack, L.L.P.
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