Note: Descriptions are shown in the official language in which they were submitted.
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Title: A screw with a double thread and a recess in the side of the shank
Technical Field
5. The invention relates to a screw with a double thread and a recess in the
side of the
shanl~.
Back.g_round Art
It is a well-known fact that screws have a tendency to spread the wood fibres
instead
j of cutting said wood fibres, especially when said screws are used close to a
side of a
piece of wood, and accordingly said screws leave a tendency to split said wood
on
both sides of the screw. As a result, not ozaly the wood is destroyed, but the
tighten-
i . ing grip of the screw in the wood is much too poor. When the fibres are
not cut up
during the insertion of the' screw, said fibres are arranged as a bow
surrounding the
1 core of the screw. As a result, the screw is subjected to an intense
pressure, which in
turn involves a high fziction oaunteractir~g the screwing movement.
; . In addition, it is known to provide screws with a recess leaving a portion
of the
j ZO ' screw without threads an,d extending into the shank of said screw. Such
a single re-
cess does not ensure the ndcessary cutting up of the wood fibres duriztg the
screwing
movement.
Disclosure of Izivention
The object of the invention is to provide a screw which efficiently cuts up
the wood
fibres during the screwing ri~ovement, and which avoids a splitting of said
wood dur-
ing the screwing movement.
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The above object is obtained by the screw including two recesses arranged
diametrically opposite
one another, where each recess is shaped as two plane segments extending
substantially parallel
to the axis of the screw and along a portion of the shank length.
As a result two cut surfaces are provided, where the two cutting edges thereof
are arranged
diagonally opposite one another while a clearance is simultaneously
established, said clearance
being positioned ahead of the cutting edges during the screwing movement. As a
result, the
wood fibres have a tendency to nestle against the plane surfaces of the
recesses between the
thread-cutting edges prior to meeting the succeeding two cutting edges which
efficiently cut up
the wood fibres in such a manner that the risk of a splitting of the wood has
been minimized.
The recesses are suitably of such a length that they extend from the tapering
portion of the screw
and a short distance over a portion where the root diameter of the screw
presents the same size
everywhere. A double thread renders it possible to keep the length of the
recess relatively short
in such a manner that the strength and retaining force of the screw are not
significantly reduced.
According to a particularly advantageous embodiment of the invention, each
recess can cut off
from approximately 0.15 mm to approximately 0.5 mm of the core diameter
extending
perpendicular to the plane side of the recess farthest away from the tapered
end of the screw.
Finally, the recesses may extend up to a distance of from approximately 6.0 mm
to approximately
14.0 from the tapered end of the screw, whereby it is ensured that a suitably
good result is
obtained in connection with most screw dimensions.
Brief Description of the Drawing
The invention is explained in detail below with reference to the drawing, in
which
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FIG. 1 is a front view of a portion of a screw according to the invention, and
FIG. 2 is a side view of the portion of FIG. 1.
Best Mode for Carrying out the Invention
The screw shown in the drawing includes two threads 1 and 2 extending in
parallel and around
the core 3 of the screw from a tapered end 4.
A plane recess 5, 6 is provided on each side of the screw, said recesses
extending parallel to one
another and parallel to the axis of the core. The recesses extend at such a
distance from the axis
of the core 3 that a segment of the core is cut off, said segment being of a
maximum height a
in the range from approximately 0.15 mm to approximately 0.5 mrn. The plane
recesses 5 and
6 extend from the tapered area of the screw in such a manner that the end
adjacent the tapered
end 4 also extends through the portions of the threads 1 and 2 within this
axea. Subsequently,
the recesses 5 and 6 extend upwards to a length b of from approximately 6.0 mm
to
approximately 14.0 mm from the tapered end of the screw. As a result, two
threaded cutting
edges 7, 7 are provided along the sides of the recesses 5 and 6, said threaded
cutting edges
cutting up the wood fibres during the screwing movement of the screw.
The above ranges of the lengths a and b depend on the dimension of each screw,
as two threaded
cutting edges 7 and 8 should, if possible, always be provided along the rirn
of the recess.
