U.S. patent number 3,891,017 [Application Number 05/444,867] was granted by the patent office on 1975-06-24 for combination screw and screwdriver with axial guide spigot.
Invention is credited to Marian Iskra.
United States Patent |
3,891,017 |
Iskra |
June 24, 1975 |
Combination screw and screwdriver with axial guide spigot
Abstract
For use with screws having a slotted head and a central axial
bore, a screwdriver blade is provided with a diametral blade tip
and a central guide spigot extending axially beyond the tip and of
greater cross-section than the top width. The spigot, which may be
cylindrical or of square cross-section, serves to maintain the
screw in co-axial relationship with the screwdriver and prevents
the blade slipping out of the slot in use. The combination of a
screw and screwdriver of the above type is described, preferably
the spigot is of less length than the depth of the axial bore to
prevent bottoming therein and, in the case of the square-section
spigot it is sized to be a press fit in the bore so that the
corners bite into the bore wall for more positive location.
Inventors: |
Iskra; Marian (Sutton
Coldfield, Warwickshire, EN) |
Family
ID: |
10006432 |
Appl.
No.: |
05/444,867 |
Filed: |
February 22, 1974 |
Foreign Application Priority Data
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Mar 15, 1973 [GB] |
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12536/73 |
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Current U.S.
Class: |
81/436 |
Current CPC
Class: |
B25B
15/007 (20130101); F16B 23/0015 (20130101) |
Current International
Class: |
B25B
15/00 (20060101); F16B 23/00 (20060101); B25b
015/02 () |
Field of
Search: |
;145/5A,5D ;81/53.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,476 |
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Apr 1875 |
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GB |
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375,680 |
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Apr 1964 |
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CH |
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Primary Examiner: Kelly; Donald G.
Assistant Examiner: Davidson; Marc R.
Attorney, Agent or Firm: Norris & Bateman
Claims
I claim:
1. The combination of a screw having a head including a transverse
parallel-sided slot and a central axial cylindrical bore of greater
depth than the slot and of constant diameter throughout its length,
which diameter is greater than the width of the slot; and a
screwdriver blade comprising a straight edged diametrally extending
blade tip for rotational driving engagement with said slot and a
central guide spigot porjecting axially substantially beyond the
blade tip for operative entry into said axial bore and having a
square lateral cross-section substantially greater in width
throughout its length than the width of said tip for engagement in
said axial bore, the diagonal of said spigot being substantially
equal to the diameter of the axial bore, and said spigot being
slightly tapered toward its free end and dimensioned to have a
press fit in said bore, whereby the corners of said spigot are
adapted to have biting engagement with the wall of said axial
bore.
2. The combination according to claim 1 wherein the axial bore is
somewhat greater in depth than the length of the spigot.
3. The combination according to claim 1 wherein the length of the
axial bore is at least twice the depth of the slot.
4. The combination according to claim 1 wherein the cross-sectional
area of the material of the screw around or adjacent to the bore is
not less than the cross-sectional area of the material at the
thread roots.
5. The combination according to claim 1 wherein the screw is a
countersunk-headed woodscrew.
Description
This invention relates to screwdrivers and screws for use
therewith, particularly hand screwdrivers, although it is
contemplated that the invention also has application to screwdriver
bits for use in power tools and automatic machines and the term
"screwdriver blade" is used hereinafter to include such bits except
where the context shows otherwise.
The disadvantages of the conventional flat bladed screwdriver used
by engagement merely in a diametral slot of the screw head are well
known, there is nothing to control axial alignment of the blade and
screw, slipping can easily occur which may damage surrounding
surfaces, and application of out-of-line torque or the use of
incorrectly sized, worn, or inaccurately ground blades often causes
damage to the screw, making the head unsightly and in some cases
making its removal difficult or impossible. In order to overcome
these disadvantages various modified forms of screw head and
screwdriver have been developed, but in many cases these
alternative arrangements give rise to other problems, for example
the torque of the screwdriver blade may only be transmitted to a
specifically shaped recess in a central zone of the head making
damage due to excessive force more likely, the specialized blade
shapes and head recesses are expensive to produce, and the shape of
the recess usually precludes any application of a conventional
screwdriver should the specialized blade be unavailable.
The object of the invention is to provide an improved screwdriver,
and screws for use therewith, which is of particularly simple
construction, yet which is effective in use in providing positive
and safe driving engagement without risk of slipping, with
transmission of maximum torque, and, in the case of the screws,
without preventing use of a conventional flat blade.
A further object is to provide a screwdriver blade which comprises
a straight edged diametrally extending blade tip for rotational
driving engagement with a parallel-sided slot of a screwhead, and a
central guide spigot projecting axially substantially beyond the
blade tip and having a square lateral cross section substantially
greater in width throughout its length than the width of said tip
for engagement in an axial guide bore of the screw; said bore being
of greater depth than the slot and of a constant diameter
throughout its length, which diameter is greater than the width of
the slot for mating engagement with the spigot of the screwdriver
blade.
A preferred embodiment of the invention is now more particularly
described with reference to the accompanying drawings wherein:
FIG. 1 is a side elevation of a screwdriver blade,
FIG. 2 is an end view thereof,
FIG. 3 is an axial section of a screw for use with the screwdriver
of FIG. 1,
FIG. 4 is an end view of said screw,
FIG. 5 is a perspective view of the screwdriver blade, and,
FIG. 6 is a side elevation of the head of the screw.
Referring firstly to FIGS. 1 and 2, a screwdriver blade 10 has a
cylindrical shank 11, one end of which (not shown) is releasably or
permanently mounted in a handle for manual use, or is operatively
engaged by a chuck or the like of a power tool. The acting end of
shank 11 is tapered to form a tip 12 having a transverse straight
edge 13 extending across the full diameter of the shank in the
manner of a conventional screwdriver blade; and on the axis of the
shank there is provided a central square section guide spigot 14
projecting axially beyond the blade edge and having a width greater
than the thickness of the tip 12 at the edge 13 as best seen in
FIG. 5.
Screws for use with this screwdriver may have conventional head
profiles, e.g., round, cheese-head, etc. FIGS. 3, 4 and 6
illustrate one example, a woodscrew having a countersunk head 15
which is provided with a transverse diametral slot 16 in the manner
of a conventional screw (thus the conventional flat screwdriver
blade can be employed if necessary although it is preferred to use
the screwdriver of the invention). Head 15 is provided with a
central axial cylindrical bore 17 whose diameter is somewhat
greater than the width of slot 16 and which extends axially into
the head to a distance preferably at least twice the depth of slot
16. Bore 17 has a diameter substantially equivalent to the diagonal
cross-sectional dimension X of spigot 14 of the screwdriver blade,
and the depth of bore 17 provides a slight clearance ensuring that
spigot 14 does not "bottom" therein, to ensure that the blade edge
13 seats fully in the slot 16 in use.
The guide spigot 14 enables the screw to be carried on the blade
into inaccessible positions which cannot be reached by hand.
Moreover, spigot 14 positively maintains the screw in true co-axial
alignment with the screwdriver shank 11 so that the screw is easily
"started" at the desired angle with the workpiece (particularly in
the case of woodscrews or self-tapping screws) and/or is easily
correctly mated with existing threads in the workpiece if being
driven into a pre-tapped bore. The screw can then be rapidly and
positively driven home without special care or effort on the part
of the user as the blade cannot easily be displaced from its
engagement with the screw while axial pressure is being applied,
thus misalignment and consequent damage is avoided.
Even when the screw has been driven home several times its head
should remain unmarked and there will be no damage to surrounding
surfaces. The risk of injury to an operator's fingers is also
minimized.
It has been found in practice that the invention is particularly
convenient in driving woodscrews home into wood-work rapidly and
accurately in almost any situation as in the assembly of furniture
and interior fitments, a "pump" type of screwdriver can be used
without fear of slipping or damage. The invention may also
facilitate the removal of tight or rusted screws.
Preferably, spigot 14 is very slightly tapered towards its free end
and bore 17 is dimensioned to be a press fit thereon, thus when the
screwdriver is first engaged with the screw, the corners of spigot
14 bite slightly into the wall of bore 17 and locate the screw
positively on the end of the screwdriver blade, thus the screw may
be carried on the blade into a position otherwise difficult of
access without fear of the screw dropping off.
The square section spigot 14 facilitates manufacture of the
screwdriver in that the machining necessary to provide a
cylindrical spigot is avoided, and it can be forged or otherwise
shaped by the same processes used to form the remaining parts of
the blade tip.
As the guide bore of the screws may extend beyond the head into
their shanks the dimensions are preferably chosen so that there is
not excessive weakness at this point, the cross-sectional area of
the screw material around or adjacent to the bore should be not
less than the cross section of the material at the thread roots so
that maximum strength is provided.
* * * * *