AU742464B2 - Stitching screw - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: Actual Inventor: Address for Service: RODNEY GEORGE WADE RODNEY GEORGE WADE CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

Invention Title: STITCHING SCREW Details of Associated Provisional Application: No. PP5298 filed 18 August 1999 The following statement is a full description of this invention, including the best method of performing it known to me: STITCHING SCREW BACKGROUND OF THE INVENTION This invention relates to screws and in particular to "stitching screws." Stitching screws are screws used to fasten together two or more thin structured substrates such as sheet metal, mesh and the like. They mostly consist of a taper screw-thread with a screw-driver accommodating head. The taper typically extends from the tip of the screw to the underside of the head.

One problem with the aforementioned type of stitching screw is that as it screws into the layers of the various structured substrates, a small gap arises between the layers due to adjacent layers being picked up by different turns of the screw thread. That is, a leading layer may be separated from a following layer by two or more turns of the thread. Such a gap is maintained as the screw is screwed its full length and even when the leading layer is tightly held under the head of the screw. In many instances, the gap can be eliminated by over-tightening the screw, however this leads to stripping of the sides of the opening in the structured substrates which can lead to a loss in the 25 integrity of the product due to weakening or removal of corrosion inhibiting coatings and the like.

OBJECT OF THE INVENTION It is therefore an object of the invention to provide a stitching screw which obviates or reduces the aforementioned problem and/or provides the public with a useful alternative.

SUMMARY OF THE INVENTION According to the present invention there is provided a stitching screw for fastening two or more thin structured substrates together, which screw is characterized by an external spiral right-handed thread which terminates below the screw head by a spacing which is commensurate with the total thicknesses of the substrates being fastened together, and wherein the terminal turn of the screw thread directly below the screw head presents a surface facing the undersurface of the screw head which is substantially parallel to the undersurface of the screw head.

DETAILED DESCRIPTION OF THE INVENTION The provision of a section of the screw shank without a screw thread enables the screw to freely rotate when the layer of the first substrate has been screwed under the head of the screw. This enables the layer of the second substrate to be screwed against the first substrate without the formation of any gaps between the two substrates and without the sides of the substrates being stripped of their coatings.

The provision of the parallel or flat surface 20 on the terminal or uppermost thread of the screw thread ensures that both substrates are maintained in parallel *alignment at the point of fastening.

o*o* By these means, a tight, integrally formed 25 connection is ensured, which addresses the previously mentioned problems of gap formation and/or stripping of the substrates.

The invention also enables two or more layers of substrates to be brought together without the need for those substrates to have been held against each other to start with. That is, the stitching screw can be screwed fully into one substrate to begin with and then screwed into the second and subsequent layers afterwards.

The stitching screw according to the invention is preferably formed with a single thread having a minimal number of turns compared with conventional threads. Since the connected layers are not held between the turns of the thread, there may be as few as two turns. Generally, however there will be approximately four turns to assist in the take-up of the individual layers and to enable easy manipulation, particularly when the screws are modified to be self-tapping. In this latter instance, the screw-thread will be a taper, that is, it will be formed on the surface of a cone.

In general, the screw thread will be formed on a shaft which extends from a cone at its tip to a cylinder beneath the screw head. The thread will suitably have a pitch of between 2 and 4 mm, preferably :about 3 mm, and a thickness of between 1 and 2 mm, 15 preferably about 1.5 mm. The thread can be truncated to produce a surface of between 0.25 and 0.75 mm, preferably about 0.5 mm.

As mentioned previously, the region of the 20 shaft of the screw on which no thread is formed and which is directly below the head of the screw, is commensurate *with the total thicknesses of the substrates being joined together. By this it is intended to mean that when substrates are brought together under normal holding 25 forces, they will occupy the space below the head of the screw in a snugly fitting manner. That is, there will be no excessive clamping of the substrates together which could lead to undue strain on the screw and there is no slackness which would enable relative free movement of the substrates with respect to each other.

In practice, stitching screws will be designed for the specific task they have to perform. The most common usage will be to join sheets of metal and/or mesh together. In the case of mesh, the diameter of the shank beneath the head of the screw will conform substantially with the diameter of the mesh opening and the non-threaded region of the screw will equal the combined thickness of the mesh and the other substrates to which it is to be fastened.

Other specific screw designs will be predicated upon the functional requirements for the screw and include parallel screw threads, taper screw threads, combined parallel/taper screw threads, and varying thread pitches, configurations and numbers.

The stitching screw according to the invention will be preferably fabricated from plastics material such as UV grade high density polyethylene, but conventional metal materials such as zinc plated steel and the like 15 can obviously also be used.

o oo The screw head may be formed with any conventionally-shaped recess to accommodate the type of fixing tool which it is going to be used with. Preferably a square recess is formed in the head so that a square profile bit or a bladed screw-driver can be used to fasten the screw.

DESCRIPTION OF THE DRAWINGS Figure 1 is an elevational view of a stitching screw according to the present invention; Figure 2 is an elevational view of the stitching screw shown in Figure 1 which has been fastened to a single substrate; and Figure 3 is an elevational view of the stitching screw shown in Figure 2 which has been fastened to two substrates.

DESCRIPTION OF PREFERRED EMBODIMENT A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in all which, like reference numerals refer to like parts.

The stitching screw 10 comprises an external right-spiral thread 11 formed about a shaft 9 which is cylindrical along its upper section 12 and conical along its lower section 13. A flat head 14 with a slot 7 is formed on the cylindrical end of the screw.

The thread 11 comprises four turns, the upper one of which (no. 15 as illustrated) has a flat upwardly facing surface 16 which is parallel to the flat surface 17 on the underside of the screw head 14. The first or lowermost screw thread 6 is tapered and inclined relative to the other screw threads to assist insertion in the substrate layers.

e*ee The screw is fabricated from ultraviolet grade high density polyethylene and has the following dimensions: "Overall length 15 mm coo *Thread pitch 3 mm Diameter of head 10 mm Length of thread 11 mm Space under head 2.5 mm Diameter of shaft 5.0 mm (max.) It is particularly adapted to stitch two sections of welded steel mesh together as illustrated in Figures 2 and 3 to which reference is now made.

When the screw 10 is screwed into the first layer 20 of mesh, the screw winds down until the mesh reaches the space between the screw head 14 and the uppermost thread 15. Here the mesh is free to rotate as there are no perpendicular forces applied to the mesh to restrain it. As a consequence, continued rotation of the screw does not damage the mesh or strip it of its coating.

The second layer of mesh 21 is then screwed to the first layer 20 until it reaches the same region as is occupied by the first layer. Continued screwing causes the second layer to push the first layer up snugly against the bottom surface 17 of the head until the lower surface of the second layer 21 is retained on the flat surface 16 of the top thread, thereby forming a secure and rigid fixture.

:It will, of course be realised that both the first and second layers 20, 21 can be joined simultaneously without the need to fasten them one at a time as described above.

The stitching screw of the invention overcomes the previously mentioned problem of existing stitching screws in a very useful and cost-effective manner.

Whilst the above has been given by way of illustrative example of the invention, many modifications 25 and variation may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set forth.

Claims (8)

1. 2. A stitching screw as claimed in claim i, wherein the screw thread is formed on a shaft which has a conical 15 shape at its tip which integrates into a cylindrical shape e.L beneath the screw head.
2. 3. A stitching screw as claimed in claim 2, wherein S0 approximately one half of the shaft is conical and one 20 half is cylindrical. 90000* 0 0*o
3. 4. A stitching screw as claimed in any one of the preceding claims, wherein the screw thread has four turns.
4. 5. A stitching screw as claimed in any one of the preceding claims, wherein the thread has a pitch of between 2 and 4 mm.
5. 6. A stitching screw as claimed in any one of the preceding claims, wherein the thread has a thickness of between 1 and 2 mm.
6. 7. A stitching screw as claimed in any one of the preceding claims, wherein the first thread on the tip of the screw is designed to assist self-tapping into the substrate.
7. 8. A stitching screw as claimed in any one of the preceding claims, which is manufactured from UV grade high density polyethylene.
8. 9. A stitching screw for fastening two or more thin structured substrates together substantially as herein described with reference to the accompanying drawings. DATED this 5th day of August 1999 RODNEY GEORGE WADE By his Patent Attorneys CULLEN CO. S. S f