NZ758521A - A Screw - Google Patents

Abstract

The invention of the present application provides a screw comprises a shank terminating in a head at one end and a tip at the opposite end. The shank has a constant diameter portion and a variable diameter portion tapering towards the tip. The shank comprises a first threaded portion extending from a twin start thread at the tip towards the head. The threaded portion includes a larger diameter thread alternating with a smaller diameter thread, and the threaded portion has a plurality of longitudinally extending swarf removal channels defined by notches formed in adjacent threads. The alternating high and low threads minimize cracking and splitting and reduce torsional resistance, and the swarf removal channels prevent slowing of the advancement of the screw into the timber.

Description

A Screw Field of the invention The present invention relates to screws for fastening timber battens or other materials.

Background of the invention "Bugle Batten" type screws are used for fastening heavy timbers such as house frames, treated pine sleepers in landscaping applications, fastening of timber boardwalks and heavy decking boards etc. Traditionally, these screws have been sold with a standard coarse thread and may include a countersunk bugle head.

One problem associated with traditional Bugle Batten screws is that when the screw is being installed in a heavy timber piece, a large amount of torsional resistance is produced because of the coarse and/or constant thread of the screw. Another problem is associated with the timber swarf that is produced as the screw thread engages and advances into surrounding timber. The timber swarf is likely to slow the advancement of the screw into the timber.

There is, therefore, a need in the art for providing an improved screw which aims to address at least some of the shortcomings of prior art screws.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the invention In accordance with an aspect of the invention, there is provided a screw comprising a shank terminating in a head at one end and a tip at the opposite end, the shank having a constant diameter portion and a variable diameter portion tapering towards the tip, the shank comprising a first threaded portion extending from a twin start thread at the tip towards the head, the first threaded portion including a larger diameter thread alternating with a smaller diameter thread; wherein the first threaded portion has at least one longitudinally extending swarf removal channel extending at least substantially the length of the first threaded portion, and the at least one longitudinally extending swarf removal channel is defined by notches formed in adjacent threads, and wherein the first threaded portion has a shank slot extending from the tip towards the constant diameter portion of the shank.

In one aspect, the screw has a plurality of equi-spaced and partially helical swarf removal channels which are defined by radially offset notches formed in adjacent threads.

In an embodiment, the first threaded portion has a reduced pitch at the commencement of the twin start thread The top and bottom surfaces of the thread may have trailing and leading angles in the region of 10°and 20° respectively, relative to a transverse axis of the screw.

In an embodiment, the first threaded portion of the screw has a shank slot extending from the tip towards the constant diameter portion of the shank.

The shank slot may extend past at least a first fully formed thread on the constant diameter portion.

The screw may have a zinc-nickel coating.

In an embodiment, the screw has a bugle-shaped head with a recessed driving socket.

An underside of the head of the screw may be formed with self-embedding ribs.

In an embodiment, the shank comprises a second threaded portion spaced from the first threaded portion and proximal to the head for enhancing clamping performance of the screw. 1002781051 In an embodiment, the screw has three equi-spaced and partially helical swarf removal channels which are defined by radially offset notches on adjacent threads.

Brief description of the drawings Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a front view of a screw in accordance with a first embodiment of the invention; Figure 2 shows a perspective view of the screw as shown in Figure 1; Figure 3 shows a bottom view of the screw; Figure 4 shows a perspective view of a screw in accordance with a second embodiment of the invention; and Figure 5 shows a side view of a top part of a screw in accordance with a third embodiment of the invention Detailed description of the embodiments Referring to Figures 1-3, there is shown a screw 10 in accordance with a first embodiment of the invention. The screw 10 comprises a shank 11 that terminates in a head 12 at one end and a tip 13 at the opposite end. The shank 11 has a constant diameter portion 15 for the majority of its length and is formed with a tapered portion 16 towards its tip 13.

The shank 11 has a threaded portion 14 that extends from the tip 13 towards the head 12, and a non-threaded portion 14c located near the head 12. It will be appreciated that the relative lengths of the threaded and non-threaded portions of the screw 11 may vary. At the tip 13, the threaded portion 14 starts off as a twin or double start thread. The twin start thread has two separate threads which extend upwards along the body of the shank 11.

The major diameter of the first thread 14a of the threaded portion 14 is larger than the major diameter of the second thread 14b. These two threads are arranged in a 1002781051 manner that the larger diameter thread 14a alternates with the smaller diameter thread 14b to form a "high-low" thread pattern. The advantage of a high-low thread pattern in the fastening of timbers is that it reduces torsional resistance during installation of the screw.

The larger diameter thread may have a diameter of 7-8 mm, preferably 7.50-7.60 mm, more preferably 7.55 mm. The smaller diameter thread may have a diameter of 5.50- 6.50 mm, preferably 6.00-6.10 mm, more preferably 6.05 mm.

A magnified cross-sectional view of a single thread of the screw 10 is shown in Figure 1. The top surface 17a and bottom surface 17b of the thread have trailing and leading angles in the region of 10°and 20°, respectively, with a transverse axis of the screw 10.

The threaded portion 14 has longitudinally extending swarf removal channels. In Figure 2, the threaded portion 14 is shown to have three equispaced swarf removal channels, but it is clear that the number of channels may vary, typically from one to four.

The swarf removal channels are formed in the threaded portion 14 by cutting out radially offset notches 22 into outer portions of the threads of the screw 10 in a helical pattern.

These channels allow an easier path for the wood swarf to be removed at a faster rate while the screw is advancing in timber. It will be appreciated that with the threads running in the clockwise direction the swarf removal channels may similarly arranged in the clockwise direction as illustrated or alternatively in the counter-clockwise direction.

The first few threads (1, 2 or 3-5 threads) at the commencement of the twin start thread at the tip 13 may have a reduced pitch compared to the pitch of the main threaded portion of the shank 11. This improves the starting performance of the screw when installed in timber. The reduced pitch near the tip 13 is roughly 0.6-0.8 times the pitch of the main threaded portion of the screw 10.

As shown in Figure 2, the head 12 has a flat top surface 12a which has a countersunk feature shown as a recessed driving socket 21. The features of flat top 12a and recessed driving socket 21 allow the screw 10 to completely flush with the timber surface when fully inserted. Although, the socket 21 is shown to be of hexagonal shape in this embodiment, other shapes and geometries, for example, square, octagonal or triangular can also be adopted. 1002781051 The screw 10 has a bugle shaped head 12b. In an embodiment, the bugle shaped head 12b can be provided with self-embedding ribs 24. The concave sides of the head aim to reduce splitting of timber by providing a more gradual transition. The head 12 of the screw has a flat top surface 12a comprising a recessed driving socket (visible in Figure 2). In an embodiment, the head 12 can be of tapered shape instead of bugle shape.

A tapered shaped head has a straight line which runs at an angle to join the head and the shank of the screw.

In this embodiment, the socket 21 is shown as a mono-countersunk feature. Other embodiments may include a double countersunk feature.

In an embodiment, the head 12 has a diameter of 8.0-15.0 mm, preferably 10.0- .0 mm.

The threaded portion 14 also has a shank slot 23 extending from the tip 13 towards the constant diameter portion 15 of the shank 11. In an embodiment, the slot 23 extends past at least the first fully formed thread on the constant diameter portion 15. The shank slot 23 allows the wood swarf to easily advance upwards into the swarf removal channels as the screw is advancing in timber. In an embodiment, the screw 10 is made of low carbon steel and is electroplated with a zinc-nickel coating that protects the base material of the screw from corrosion.

Figure 4 shows a perspective view of a screw 40 in accordance with a second embodiment of the invention. In this embodiment, a second threaded portion 41 is provided at the top of the shank in addition to the features of the screw 10 as discussed above in Figures 1-3. Similar to the first threaded portion 42, the second threaded portion 41 may also comprise alternating high-low diameter threads, and one or more swarf removal channels. The second threaded portion 41 is also known as a top grip thread.

The presence of the top grip thread enhances the clamping performance of the screw and is particularly advantageous when fastening multiple pieces of timber.

Figure 5 shows a side view of a top part of a screw 50 in accordance with a third embodiment of the invention. The screw 50 has a first threaded portion 52 (only partially shown) which is similar to first threaded portions 14 and 42 of screws 10 and 40, respectively. The top grip thread 51of the screw 50 does not comprise swarf removal 1002781051 channels and does not have the alternating high-low diameter thread. The Top Grip thread 51 has a constant diameter thread with diameter of 6.00-6.50 mm, preferably 6.20- 6.30 mm. In the particular embodiment as illustrated the outer diameter of the thread 53 is 5.50-6.50 mm, preferably 6.05 mm. The diameter of the shank 54 is 5.0-6.0 mm, preferably 5.3-5.5 mm, more preferably 5.4 mm.

In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

As used herein the terms "include" and "comprise" (and variations of those terms, such as "including", "includes", "comprising", "comprises", "comprised" and the like) are intended to be inclusive and are not intended to exclude further features, components, integers or steps.

It will be understood that the embodiments disclosed and defined in this specification 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 embodiments.

Claims (11)

1. A screw comprising a shank terminating in a head at one end and a tip at the opposite end, the shank having a constant diameter portion and a variable diameter portion tapering towards the tip, the shank comprising a first threaded portion extending from a twin start thread at the tip towards the head, the first threaded portion including a larger diameter thread alternating with a smaller diameter thread; wherein the first threaded portion has at least one longitudinally extending swarf removal channel extending at least substantially the length of the first threaded portion, and the at least one longitudinally extending swarf removal channel is defined by notches formed in adjacent threads, and wherein the first threaded portion has a shank slot extending from the tip towards the constant diameter portion of the shank.

2. The screw of claim 1, wherein the shank comprises a second threaded portion spaced from the first threaded portion and proximal to the head for enhancing clamping performance of the screw.

3. The screw of claim 1 or 2, wherein the at least one longitudinally extending swarf removal channel is one of a plurality of equi-spaced and partially helical swarf removal channels which are defined by radially offset notches formed in adjacent threads.

4. The screw of claim 3, wherein the plurality of equi-spaced and partially helical swarf removal channels is three equi-spaced and partially helical swarf removal channels.

5. The screw of any one of the preceding claims, wherein the first threaded portion has a reduced pitch at the commencement of the twin start thread.

6. The screw of any one of the preceding claims, wherein the top and bottom surfaces of the thread has trailing and leading angles of 10°and 20° respectively, relative to a transverse axis of the screw.

7. The screw of any one of the preceding claims, wherein the shank slot extends past at least a first fully formed thread on the constant diameter portion.

8. The screw of any one of the preceding claims, wherein the screw has a zinc- nickel coating.

9. The screw of any one of the preceding claims, wherein the head is a bugle- shaped head with a recessed driving socket.

10. The screw of claim 9, wherein an underside of the head comprises self- embedding ribs.

11. The screw of any one of the preceding claims, wherein the smaller diameter thread is substantially coextensive with the larger diameter thread.