Note: Descriptions are shown in the official language in which they were submitted.
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A tool and countersinking screw
Field of the invention
The present invention relates to screwdriving tools, and combinations of
screwdriving and countersinking tools as
well as to countersinking screws.
Background of the invention
Medium Density Fibreboard (MDF) such as that known under the trade mark
CRAFTWOOD, is manufactured
from a combination of resin and very fme wood fibres. During the manufacturing
process some types of MDF are
finished with a very dense outer surface which is given to provide the surface
with a very smooth finish so that the
board can be painted or otherwise coated without the need to sand. The
elimination of sanding give such board the
advantage that dangerous dust is not generated and removes a whole process
step before a finial finish is given.
This has led to a very wide acceptance of such MDF. Other materials such as
masonite also have a dense outer
layer but such a material is not as dense as MDF.
A dense outer layer of MDF causes difficulties for trades people when
assembling such MDF into a structure such
as for example architraving, skirting board or frame or boarder material. Such
operations are typically carried out
using sophisticated self tapping screws which were developed for fibre board
use. Such screws do not have self
drilling capability as the self drilling capability adds greatly to the cost
of such screws. The fibre board screws tend
to have only a sharp point which is designed for softer material whereby
application of pressure to the point embeds
the point into the material so that the start of the thread is actually in the
material. However when such screws are
used with MDF, the sharp screw point does not penetrate the dense outer layer.
This can have disastrous results for
the tradesperson, as they are normally applying great force and may result in
the screw slewing off in one direction.
This will can cause injury to the tradesperson or damage to the MDF workpiece
as well as be generally
inconvenient.
A time consuming, and fiddly fabrication function is the need to countersink a
screw into a surface into which a
screw is to be assembled. Countersinking represents another difficulty for a
tradesperson which is exacerbated
when MDF is involved.
This countersinking can be done by drilling a pilot hole, countersinking the
pilot hole and then driving in the screw.
With the advent of self-drilling and tapping screws and powered screwdrivers,
pilot holes no longer required to be
drilled.
Some self-tapping, self drilling screws do have formations on a countersinking
head which are adapted to assist the
screw to countersink itself as the screw rotates and the head engages the
surface. However by the time the
countersinking head has reached the surface in which it is to be counter sunk
the speed of the screw has been
reduced. This reduces the ability of the formations on the screw's head to
properly countersink. One difficulty with
self-drilling self tapping screws is that many of them never fully
countersink. This is because once they reach the
surface, the power to drive may not be sufficient. Or alternatively, sometimes
they snap by virtue of the amount of
power being used to drive the screw in.
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Another difficulty which can occur is that the female thread can strip inside
the material if the screw is rotated with
too much power or speed.
These are some of the many difficulties which can occur with countersinking
screws. To date the problem of
countersinking screws has been troublesome and annoying. Some of these
problems are exacerbated when
countersinking is required to be done in materials which have a very dense or
hard outer surface and this surface
must first be breached before ease of countersinking occurs. Examples of such
materials include a custom board or
MDF board which material may also be sold under the trade mark CRAFTWOOD.
Disclosed in US patent 3207196, issued and published on 21 September 1965, is
a countersinking tool which
combines a screw driving bit and counter sinking bit. However, the
countersinking bit is stated to be an abrading,
wearing or rubbing bit so as form a depression. Because of this abrading
feature, the cutting tool of US 3207196 is
not able to form a depression into modern materials such as MDF-board as such
boards have a very dense outer
surface.
Some countersinking screw heads are manufactured so as to include a series of
elongated triangular prism
formations along the slant height of a countersunk head. These prism
formations have a great deal of difficulty
counter sinking a screw in an MDF-board due to the density of the surface of
the board. One difficult is that MDF's
density leads to the head of the screw fracturing from the shank.
If the screw head does not fracture from the shank, another difficult is that
it can take several attempts at tightening
and loosening the screws so as to be able to properly counter sink the head
into the surface of an MDF-board.
These prisms, due to the extra steps needed to countersink the heads of
countersinking screws, are generally
inefficient.
It is an object of the present invention to provide a countersinking screw
which ameliorates, at least in part, at least
one of the disadvantages of the prior art.
Summary of the Invention
The invention provides a screwdriving tool having
a shank adapted to be rotationally driven about its longitudinal axis; and
a cutting tip located on the screw driving tool at the end opposite to said
shank, said cutting tip
being laterally off set from said longitudinal axis so as to produce a starter
hole for a self tapping
screw when the said tool is pressed against a surface and the tool is rotated.
The at least one cutting tip, or each cutting tip when there is more than one
cutting tip, is that part of the tool which
is located at the furthest distance away from the shank, measured in a
direction which is parallel to said longitudinal
axis.
The screwdriving tool can be of a flat blade variety or a four blade variety
such as cross shape or Phillips head
type.
The cutting tip can be formed by a concave cut out intersecting with the screw
driving end with the cutting tip
converging to either a point or a surface.
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The invention provides a screwdriving and countersinking tool having a narrow
end and a broad end said narrow
end having a screw engaging means so as to be able to drive a screw when said
screw engaging means has engaged
a screw, said tool having formed thereon, between said narrow end and said
broad end, a countersinking means,
said narrow end including as part of said screw engaging means a shearing
means to allow said narrow end to
engage a surface to be countersunk and to remove material from said surface
when said tool is rotated.
Preferably said tool has, when viewed in side elevation, a generally
triangular configuration.
Preferably said tool has a generally pyramidal shape.
Preferably said tool has a generally conical shape.
Preferably said tool has one or more screwdriving members as its screw
engaging means.
Preferably said tool has a Phillips head configuration as its screw engaging
means.
Preferably screw engaging means has at, at least one terminus, said shearing
means.
Preferably said tool includes at least one continuous shearing formation which
is located between said narrow end
and said broad end.
Preferably said tool includes more than one discontinuous shearing formation
which are located between said
narrow end and said broad end.
Preferably said more than one discontinuous shearing formations are
overlapping.
Preferably said shearing formations and other parts of the tool which are not
insertable into a screw head, are able
to perform the countersinking function, and at the same time are safe to
contact when the tool is rotating.
Preferably said shearing formations are formed from cuneiform or triangular
elongated shearing members.
Preferably said countersinking means operates to form a countersunk recess in
a material by rotating in a direction
which is opposite to the direction said tool must rotate to drive as screw
into said material.
The invention also provides a screwdriving tool to drive a screw into a
surface, said tool including a converging
screw engagement end which has a formation to engage a screw, said formation
also forming part of a
countersinking means formed on the remainder said tool, wherein said
countersinking means is also formed on said
engagement end with said countersinking means at least in part being
insertable into a recess in said screw, said
recess being used to drive said screw into a surface.
Preferably said countersinking means operates to form a countersunk recess in
a material by rotating in a direction
which is opposite to the direction said tool must rotate to drive said screw
into said material.
The invention also provides a countersinking screw having slot located in a
head for driving said screw and a
threaded shank extending away from said head, said screw having a longitudinal
axis of rotation around which said
screw is constructed, said head being of a generally conical formation which
is converging in the direction from
said head to said threaded shank, said head having at least one discontinuous
circumferential surface therearound,
said head including at least one blade portion thereon, said blade potion
being characterised by a cutting surface
which lies in a plane which is at an angle relative to a plane which includes
said axis of rotation, said head being
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further characterised by the said at least one circumferential surface
starting at a first slant line location and ending
at a second slant line location, said first slant line location being at a
first end of said cutting surface and said
second slant line location being at a second end of said cutting surface, said
first end of said cutting surface being
radially displaced away from said axis of rotation by a distance which is
greater than the radial displacement of said
second end of said cutting surface.
Preferably said screw includes at least one blade portions on said
countersinking head and the same number of
broken circumferential surfaces around said countersinking head.
Preferably there is more than one blade portions equi-spaced on said
countersinking screw head.
Preferably said cutting surface, when viewed from a direction normal to said
cutting surface, has a generally
triangular shape.
Preferably said cutting surface converges in the direction from said head to
said threaded shank.
Preferably said cutting surface lies in a plane which contains said axis of
rotation and a radius from said axis of
rotation.
Preferably said cutting surface includes at least one surface which has its
direction defined by a direction line
normal to said surface or by a direction line normal to a tangent to said
surface, whereby said direction line is
skewed relative to said axis of rotation.
Preferably said cutting surface is a helical or part helical surface.
Preferably said cutting surface has a slope on it wherein at any point on said
surface, said surface inclines in a
direction away from said point, when said direction away from said point is
opposite to the direction required to
secure said screw into a material.
Brief description of the drawings
An embodiment of the present invention will now be described, by way of
example only, with reference to the
accompanying drawings in which:
Figure 1 is a side elevation of a combination screwdriving and countersinking
bit prior to engagement with a
countersinking screw.
Figure 2 illustrates a perspective view of the bit of Figure 1.
Figure 3 illustrates a plan view of a second embodiment of a combination
screwdriving and countersinking bit.
Figure 4 illustrates a side elevation of the bit of figure 3, prior to
engagement of a countersinking screw.
Figure 5 illustrates a plan view of a third embodiment of a combination
screwdriving and countersinking bit.
Figure 6 illustrates a side elevation of the bit of figure 3, prior to
engagement of a countersinking screw.
Figure 7 illustrates one of the bits of figures 1 to 6 in use during a
countersinking operation.
Figure 8 illustrates one of the bits of figures 1 to 6 in use during a screw
driving operation.
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Figure 9 illustrates a Phillips head screw driving bit having a gouging or
cutting tip.
Figure 10 illustrates a tlat blade screw driving bit having a gouging or
cutting tip.
Figure 11 illustrates a hexagonal blade screw driving bit having a gouging or
cutting tip.
Figure 12 illustrates a side elevation of a first embodiment of a
countersinking screw.
5 Figure 13 illustrates a side elevation of the screw of figure 12.
Figure 14 illustrates a side elevation of a second embodiment of a
countersinking screw.
Figure 15 illustrates a side elevation of the screw of figure 14.
Figure 16 illustrates a screw of figure 12 or figure 14 in use.
Detailed description of the embodiments
Illustrated in Figure 1 and 2 is a straight fluted generally conical shaped
tool 2. In side elevation as in figure 1 the
tool 2 has a generally triangular shaped profile. The tool 2 has a base 4 from
which extends a rotation shaft 6 of the
hexagonal type. The tool 2 is illustrated as a rotary bit for inserting into
an electric screwdriver or other powered
screwdriving rotation driving means such as a drill, pneumatic drill etc.
However, It will be readily understood that
the present invention can be applied to manually or hand operated tools such
as hand powered screwdrivers or
drills for that matter.
The tool 2 has a relatively broad base 4 by comparison to a relatively narrow
screwdriving end 10. The
screwdriving end 10 has a screw driving tip 8. The screw driving end 10
occupies approximately half the height of
the tool 2 , with the rest of the height of the surface engagement portion of
the tool 2 being made up of the
countersinking section 12.
The screwdriving end 10 is made up of four radiating wing/members 14, 16, 18
and 20. The wing members 14, 16,
18 & 20 have straight and parallel forward and rearward sides 1 1 and 13 which
are parallel to the longitudinal axis
5 of the shaft 6, and are radially oriented to the longitudinal axis 5. The
outer surfaces 15 of the members 14, I6, 18
and 20 are at an angle 17 to the longitudinal axis and at an angle 17A to the
straight sides 1 1 and 13 on each
member 14, 16, 18 and 20. The members 14, 16, 18 and 20 form a cross in
underneath plan view. The cross is
insertable into a cross shape cavity 22 which is generally located in Phillips
head screws 23.
At the very terminus and near the apex of the members 14, 16, 18 and 20 is a
blade portion or cutting tip 24. On the
member 14 the cutting tip 24 is an inclined plane which angles in one
direction, whereas on the member 20 the
cutting tip 24 is an inclined plane in the opposite direction when viewed as
in fig 1. All the cutting tips 24, when the
tool 2 is rotated about an axis S present the forward edge 24A to engage the
surface which will have a counter sunk
recess formed therein. The surfaces 15 A behind the cutting edges 24A are also
at an angle to the longitudinal axis
5. That is the end of the surfaces 15A furthermost from the longitudinal axis
5 are further away from the base 4 by
comparison to the opposite end of the surfaces 15A ( which opposite end is
nearest to the longitudinal axis 5). This
places each of the surfaces 15A at an angle which forms a concave end.
If desired only one of the members 14, 16, 18 or 20 need have a cutting tip 24
or 2 or more of the members 14, 16,
18 and 20 can have such blades. In the countersinking segment 12 the members
14, 16, 18 and 20 extend back
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towards the base 4 and have formed thereon at their forward edges 24B a
similar cutting edge to cutting edge to
cutting tip 24. Four additional countersinking blades 28 (see fig 1) can be
located intermediate the forward edges
24B on member 14, 16, 18 and 20 but these four additional counter sinking
blades 28 are only preferable and are
not illustrated in fig 2.
The tool 2 as illustrated in fig 2 has the countersinking segment 12
constructed from members 14, 16, 18, 20 which
extend a considerable distance radially from a central body portion 23.
However if desired the countersinking
segment 12 can be formed on a conical or pyramidal surface, with the shearing
formation projecting only a
relatively short distance away from the body.
Whilst the tool 2 has a generally triangular configuration in side elevation
as illustrated in Figure 1, it can be seen
from the Figure 2 that a pyramidal or conical shape is an appropriate
description of its overall general shape. It will
be noted in figure 1 that the tool 2 has the members 14, 16, 18 and 20
terminating in a cutting edge 53, which is
parallel to the longitudinal axis 5. Whereas, for the sake of illustration the
toot 2 of fig 2 includes no such cutting
edge 53. The effect of these differences will be discussed later.
The screw driving end 10 and countersinking segment 12 need not be continuous
all the way from the screwdriving
end 10 back to the base 4. They may need to be continuous along the length of
the respective segments but
otherwise the cutting tips and cutting edges, on the members on which they are
mounted can be angularly offset. In
which case they will need to either overlap or in side elevation one will need
to terminate in a plane which is the
beginning of the other.
Referring now to figures 7 and 8, in use the tool 6 is attached to a drill 300
or other portable rotation means. In use
the drill 300 is rotated so that the tool 2 can rotate and engage a surface
302 of a member 304 thereby
countersinking the surface to form a counter sunk recess 306 as forward edges
24A and 24B of the tool 2 engage
the surface 302. The countersinking segment 12 will progress to a depth in the
region of outer width or diameter 31
of the tool 2. The outer diameter 31 is preferably equal to or greater than
the outer diameter of the head of the
screw 23.
Depending upon the material of the member 304 into which a countersunk recess
306 is to be formed, and the type
of screw 23 utilised, it may not be necessary for the outside diameter of
countersunk recess 306 to be greater or
equal to the outside diameter of the head of the screw 23. If the
countersinking screw 23 has shearing formations or
capacity on the outside surface of the countersinking head, then the outside
diameter of the countersunk recess can
be less than the outside diameter of the screw, if the material is of a
timber, timber composite or fibre board or like
material such as custom board or MDF board.
If no prior art screw countersinking formations were present on the outside
surface of the screw 23, then the outside
diameter of the countersunk recess 306 in the member 304 may need to be equal
to or greater than the outside
diameter of the head of the screw 23.
In the case of the tool 2 illustrated in fig l, if the tool 2 is inserted into
a surface to the depth of the base 4, a
3S countersunk recess will be formed which will include a cylindrical portion
immediately below the surface. The
cylindrical portion is formed by the cutting edge 53 which is parallel to the
longitudinal axis 5. The cutting edge 53
will result in a neater, smoother, cleaner finish to the recess and can be
timber plugged or puttied if necessary.
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The absence of the cutting edge 53 from the tool 2 of fig 2, can result in the
same cylindrical portion being formed
in the material, but there is risk is that the surface and edges of the
cylindrical portion may not be as clean and
precise. The tool of fig 2 is better adapted to form only a tapered
countersunk recess without a cylindrical portion.
This does not mean to say that the tool of fig 2 could not be used to exactly
the same purposes as the tool of fig I .
Referring once again to figures 7 and 8, once the desired depth of countersunk
recess 306 has been achieved, a
screw 23 is placed on the screw driving tip 8 and the operator then depresses
the end 308 of the screw 23 into the
countersunk recess 306 in the member 304. By rotating the screw 23 (which is a
self drilling, self tapping screw),
the screw driver tip 8 and the drill 300 will force the screw 23 into the
position shown in figure 8, by rotating the
screw 23 until the top surface of the countersinking head of screw 23 is at or
below the surface 302 of member 304
into which the countersunk recess 306 was formed.
As the members 14, 16, 18 and 20 are inside the cross shaped recess 22 of the
screw 23, the cutting tips 24 and
forward edges 24A of members 14, 16, 18 and 20 will not attempt countersink
the screw head 23 because there is
no relative rotation between the screw and cutting tips 24. The absence of
relative rotation is a result of the surfaces
of the recess of the screw resting parallel to the side surfaces of the
members 14, 16, 18 and 20.
Whilst it is advantageous for those portions of the tool 2 which are engaged
into the recesses 22 of the screw to be
relatively sharp, it is preferred that the countersinking segment have cutting
edges which are not particularly sharp.
This will help to prevent injury to the user as the user may have their hand
near to the tool, to hold the screw onto
the screw driving end 10. These cutting edges need not be sharp but by virtue
of the speed of rotation of the drill
will execute an effective countersinking operation.
The cutting tips 24, the cutting edges 24A and 24B (and the cutting edge 53 if
it is present) do not necessarily need
to be sharp, or tempered and sharp, if the tool 2 is to be used with timber or
timber type products such as MDF
(medium density fibre board) custom board (as sold under the trade mark
CRAFTWOOD). However, if the tool 2
is to be utilised with metals, then the cutting edge will more than likely
need to be sharp, and possibly tempered as
well. One of the difficulties of tempering however, is that the metal of tool
2 can become brittle, and may fracture
when used as a screwdriver. However, it is expected that other treatments of
the metal will provide sufficient
strength while maintaining for as long as possible a relatively sharp cutting
edge.
In the embodiment described with respect to the drawings, there is formed a
concave end in the screw driving tip 8.
When used to countersink, this concave end will form at the base of the
countersunk recess, a relatively small and
shallow mound or conical projection. This mound or projection will not impair
the effectiveness or operation of the
tool 2. However, if desired, the concave end can be replaced by a flat planar
end, that is the cutting edges 24A are
all included in a single plane, which plane is perpendicular to the
longitudinal axis 5. Alternatively, the cutting
edges could be made to form a convex end. However, the depth of the convex end
will also be dependent upon the
size of the recess 22 in the screw 23, to ensure a proper screw driving
ability.
The tool 2 can be made of magnetic material, so that screws 23 might be
attracted to the tool 2 and thereby stay in
position, as the user threads the screw into the wall. This obviates the need
for the operator to use their free hand to
support the screw.
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Illustrated in figure 3 is a combination bit 2B to countersink and drive a
screw 23 (see tigure 4). The bit 2B has
many features in common with the features bit 2 of figures I and 2. These
similar features are like numbered with
the features of figs 1 &2. Because of this commonality the purpose and
structure of all features will not be
discussed.
The cutting edges 24B and 53 of the countersinking portion 12 when viewed in
the plan view of figure 3 includes a
cutting face 11 and rear face 13 on each of eight wing members 14, 14A, 16,
16A, 18, 18A, 20, 2UA, which
converge toward the axis of rotation 5. The cutting edges 24B and 53 of the
bit 2B are formed from the intersection
of the cutting face I 1 together with a tapered outer surface 15. The bit 2B
of figures 3 and 4 will perform its
countersinking function when it rotates clockwise in the plan view of fig 3,
which is the same direction as the
direction of rotation to drive a screw into a material or board. This is also
similar to the embodiment of figures 1
and 2.
Illustrated in figures 5 and 6 is a bit 2C similar to that of figures 3 and 4,
and like parts have been like numbered.
The difference between the bit 2B of figures 3 and 4, and the bit 2 of figures
5 and 6, is that the countersinking
segment 12 has its cutting face 1 I on the opposite sides of the wings 14,
14A, 16, 16A, 18, 18A, 20 and 20A to the
cutting faces 1 1 on the bit of figures 3 and 4. The location of these cutting
faces means that the bit 2C performs its
countersinking function in the opposite direction, namely counterclockwise in
plan view of figure 5. The bit 2C of
tigures 5 and 6 performs its screw driving functions in the same direction as
the bit of figures 3 and 4.
The wings members 14A, 16A, 18A, and 20A extend from the end proximate to the
shaft 6 or base 4 towards the
screw driving end 10, but do not extend into the screw driving end 10,
otherwise the wing members 14A, 16A,
18A, and 20A will interfere with the engagement of the screw driving end in
the slot 22 of screw 23.
The ends of the members 14, 16, 18, 20, at the lower end of the screw driving
segment 10 of bit 2C of figures 5 and
6, have inclined surfaces 15A, which are angled to provide cutting edges 24
which cut in the anti clockwise
direction. The inclined surfaces 15A are at an angle whereby the cutting edge
24 projects downwardly from the
wing members 14, 16, 18, 20, by comparison to the rearward edge of the
inclined surfaces ISA.
This feature ensures that the cutting edge 24 and surface 15A will not
interfere with or damage the driving slot in
the screw 23. The rearward face 13 of the wing members is opposite to the
cutting surfaces 11, which engages the
sides of the slot 22 of the screw 23.
To operate the bit of figures S and 6, the operator simply mounts the bit 2C
into a reversible drill or other rotary
tool. To form a countersunk recess in a material to receive the screw 23, the
operator rotates the bit 2C in an anti
clockwise direction. To cut or shave countersunk recess, the cutting edges 24B
and 53 engage and are moved or
rotated relative to the surface receiving the countersunk recess. Once the
desired depth of countersinking is
reached, the operator reverses the direction of rotation of the drill or
rotary tool. Upon doing this or before, the
operator attaches a screw such as screw 23 onto the screw driving end 10 of
the bit 2C of figures 5 and 6. By then
activating the drill or rotary tool, as the tip of the threaded end of the
screw 23 is in the base of the countersunk
recess, the screw 23 will be inserted into the material and the recess so that
the top surface of the screw 23 is at or
below the surface of the material.
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While the above described bits are illustrated including four or eight cutting
surfaces or edges, it will be readily
understood that the present invention is applicable to tools, bits and screws
having at least one, or one or more
cutting surfaces or edges.
Illustrated in figure 9 is a screwdriving tip 500 which has a central
longitudinal axis of rotation 502 and a screw
driving end 504 and a shank 506. The shank 506 includes a hexagonal drive end
508 for connection into a powered
screwdriver, drill, manual hex drive or other means to rotate the tip 500 and
thus drive screws into a surface. If
desire the shank 506 can be connected to a conventional screw driver handle.
The screwdriving end 504 is of the Phillips head variety having four
orthogonal blades 510. The blades 510 are
formed in a conventional way on the end of the shank 506. The screw driving
end 504 varies from a conventional
Phillips head screw driving end by each blade S10 terminating in a cutting,
gouging or carving tip 512, which is
formed (in this instance) by a cavity or concave recess 516 intersecting with
the blades 510. This intersection forms
cuneiform cutters which project away form a base surface 518 located at the
terminus of the screw driving end 504
at the central axis of rotation. The location of an extremity of tip 512
relative to any point on the shank 506 is a
greater distance away from that point on the shank than the location of the
base surface 518.
The tips 512 terminating in an edge 520 is the preferred arrangement, however,
if desired they could be made to
terminate with a point, or even a rounded edge or surface .Any appropriate
terminus can be used which will allow
the tip 512 to cut into a material into which a screw is to be inserted.
The embodiment of figure 9 is illustrated as being of the Phillips head
variety. However, the invention embodied in
figure 9 can be embodied in a flat head type screw driver, or other type of
screw driving formations. For example in
figure 10 the flat blade screw driver tip 530 has a concave recess 532 in its
tip 534, which forms a cutting, gouging
or carving tip 536 at the ends of each of the blades 530. Whereas in figure 11
is a hex drive tip 540 as is used to
drive screws with a hex recess in their head. The tip 540 has six cutting,
gouging or carving tips 542 at each of the
apexes between adjacent sides of the hex tip 540.
In operation, the screwdriving tips 500, 530 or 540 are used in the following
manner. The bit 500, 530 or 540 is
inserted into a drill, screwdriver or handle. The tip is then placed against a
surface into which a screw is to be
inserted so as to cut, gouge or carve the surface to expose a softer under
surface which is usually present under a
dense layer such as exists in MDF. Once a small cut, gouge or carving has been
made, the tradesperson removes the
tip from the surface, to expose an annular groove in the surface of the
material. This groove will have an outside
diameter equal to the maximum distance that the extremity of the tip 512, 536
or 542 is away from the central axis
of rotation. Into the annular groove, against the softer material the point of
a self tapping fibre board screw can be
positioned. As it is a less dense material or layer, the screw thread will
engage that material or layer, will the screw
head covering up the rest of the annular groove and hiding it from view.
While the above description in relation to figures 9 10 and 11 shows multiple
cutting, gouging or carving tips 512,
536 and 542, there need only be present one such tip. To ensure that the
moments applied to the screwdriving tip
are at least equal so as to prevent the screw diving tip from dancing over the
surface, it is preferable that there be
two such tips located on opposite sides of the central axis of rotation of the
screw driving bit.
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Illustrated in figures 12 and 13 is a countersinking screw 100 which has a
countersinking head 102 and a threaded
shank 103.
The screw 100 includes four cutting surfaces I 13 which extend away from the
central axis of rotation 105 in a
direction parallel to a plane containing the axis 5. The head 102 has an equal
number of circumferential surfaces
5 106, such that one circumferential surface 106 starts at the outward end of
the cutting surface t 13 and extends in a
curved path around the head 102 to terminate at the beginning of the inward
end of an adjacent and rearwardly
located (with reference to the direction of rotation to countersink) cutting
surface 113. This forms a saw tooth
pattern around the outside of the screw head 102. The cutting surfaces taper
or converge in the direction of the head
102 to the threaded shank 103 of the screw 100.
10 In use, as the screw 100 is driven into a surface in which the screw 100
must be countersunk, the cutting surfaces
1 13 will engage the surface of a material, only as the a drill or screw
drives and rotates the cutting surfaces 113.
The rotation of the screw 100 will force the cutting surfaces 113 to cut as
they simultaneously engage the material
and rotate around the axis of rotation 5 and move inwardly towards the
material.
The illustrated screw 100 has its cutting surfaces in a plane which contains
the axis of rotation of the screw 10 as
well as a radius from that axis of rotation, but this is only preferable.
In tigures 14 and 15 is illustrated a countersinking screw 100A. The screw of
figures 14 and IS has many similar
features to the screw 100 of figures 12 and 13 and like features have been
given the same reference numeral
followed by the letter "B".
In figures 14 and 15, the cutting surfaces 113A are effectively inclined
planes which slope upwardly from their
lower most starting point (closest to the shank of the screw) towards a
location which is in an anti clockwise
direction from the starting point.
The cutting surfaces 113A are illustrated as having a generally planar
outermost surface to shave or cut the material
into which the screw 100A is to be secured. However, if desired the cutting
surfaces 113A of screw t00A can be
curved or include a curved portion. In which case the direction of a part of
that cutting surface 113A, defined by a
direction line normal to the cutting surface or by a direction line normal to
a tangent to the cutting surface, is
preferably such that the direction line is skewed relative to the axis of
rotation of the screw 100A.
The cutting surface 113A as illustrated exhibits the feature that the slope on
it can be defined by considering any
point on the cutting surface between the ends of the cutting surface. The
cutting surface inclines in a direction away
from that point, the direction being generally such as to cause rotation in a
rotation direction opposite to that
required to secure said screw into a material.
Alternatively the cutting surface can be a helical or part helical surface,
but this feature is not illustrated in the
drawings.
Illustrated in figure 16 is a screw of figure 12 or 14 in use, showing how the
cutting surfaces 113 or 113A shave
and eject a shaving from the material into which the screw 100 or 100A is
being inserted. One advantage of the
embodiments of the present invention is that in use there is provided a cavity
in a forward direction (clockwise
direction in the casse of a normal right handed screw thread) which provides a
volume or space for the swarf or
CA 02321003 2000-08-17
WO 99/17908 PCT/AU98/00$34
11
shaving to be located and pass through during the operation of the screw 100
or 100A. This ensures an efficient
operation of the cutting surfaces 113 or 113A by preventing them from getting
clogged up by the swarf or shavings.
While the above described screws are illustrated including four cutting
surfaces or edges, it will be readily
understood that the present invention is applicable to screws having at least
one, or one or more cutting surfaces or
edges.
It will be understood that the invention disclosed and defined herein extends
to all alternative combinations of two
or more of the individual features mentioned or evident from the text or
drawings. All of these different
combinations constitute various alternative aspects of the invention.
The foregoing describes embodiments of the present invention and
modifications, obvious to those skilled in the art
can be made thereto, without departing from the scope of the present
invention.
