AU2010200536B2

AU2010200536B2 - Self-drilling screw

Info

Publication number: AU2010200536B2
Application number: AU2010200536A
Authority: AU
Inventors: David Collinson; John Mallet
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2010-02-12
Filing date: 2010-02-12
Publication date: 2016-09-01
Anticipated expiration: 2030-02-12
Also published as: AU2010200536A1; TW201144622A

Abstract

C:WRPonbl\DCC\PLB\2702901_ .DOC-1222OIO -7 A screw for fixing timber to an underlying timber or metal support, the screw comprising a shank having a drilling portion at one end and a head at the opposite end, the drilling 5 portion having a drilling tip with cutting edges and a fluted region extending from the cutting edge, and a thread extending from the end of the drilling portion remote from the drilling tip to a position spaced from the head whereby the screw shank has an unthreaded portion between the end of the thread and the head, wherein the drilling portion is operative to drill during application of the screw a hole having a diameter greater than that 10 of the unthreaded portion of the screw shank whereby when the screw is applied through the timber to be fixed there will be formed through that timber a clearance hole for the unthreaded shank portion. )4 8a FIGURE 1 8a C:\NRPonbl\DCC\PLB\2705399_I.DOC - 3/2/10

Description

SELF*I>RILlJNG SCREW

The present invention relates to a seif-drilling screw for iking timber, decsrngpianks tor example, to underlying timber joists or other structure.

Conventionally, when fixing timber decking planks to underlying timber structure, the ptaodee is to pre-drill the timber plank and then to use a conventional sell-drilung timber H-tew* suers as a Type 1? screw,- to fix to the underlying structure, if the timber decking plank Is not pre-drilled, direct application of a conventional self-drillingtimber screw into-the plank can cause the. plank to split at the fixing .point particularly when the screw is close to the de of ine timber, the tendency for splitting increasing the closer the screw is to the edge. Splitting can give rise to safety .issues and replacement of the decking plank is usually required if that occurs.

The present invention in its preferred embodiments provides a self-drilling timber screw whicn can be applied close to the .edge of timber decking planks) or other timber) without the need to predrill to avoid splitting.

According to the present invention, there is provided a screw lor fixing timber to an underlying timber or metal support, the screw comprising a shank having a drilling portion at one end and a head at the. opposite end, the drilling portion having, a drilling tip with cutting edges, which lead into.flutes that: extend along the length of the drilling:portion so as to define a constant effective diameter ofthe drilling portion, and a thread extending from the end of the drilling portion remote, froth the drilling tip to a position spaced from the head whereby the screw shank has an unthreaded portion between the end ofthe thread and the head, wherein the drilling portion is operative to drill during application, ofthe screw a hole having a diameter -greater than that of the unthreaded portion ofthe screw shank whereby when the screw is applied through the timber to be fixed there will be formed through that timber a clearance hole for the unthreaded shank portion.

In a preferred embodiment of the invention, the thread tip diameter is constant over at least a substantial part of its length and that diameter is at least about '0,75mm. greater than that of the drilling portion.

An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a side view of a self-drilling timber screw in accordance with the preferred embodiment;

Figure 2 is a side view looking at right angles to the view of Figure 1; and

Figure 3 is an enlarged sectional detail of the thread zone marked B in Figure 2.

The screw of the preferred embodiment of the invention has a drilling portion 2 of similar form to that of self-drilling screws designed for use into metal, namely with inclined cutting edges 4 defining the drilling tip leading into flutes 6 extending along the length of the drilling portion. The thread of the screw extends from the end of the drilling portion 2 remote from the cutting edges 4 to a position inwardly from the head 8 of the screw so as to leave an unthreaded portion 10 of screw shank between the end of the thread and the screw head. The thread form provides a constant thread tip diameter over a substantial part of the length of the thread although it is to be understood that at the outer end of the thread (its end adjacent the drilling portion 2) the thread will rise progressively from zero to full thread height over at least one and possibly two thread turns.

In the embodiment shown, the screw head 8 is a countersunk head with teeth 8a at its underside to cut a countersink into the surface of the timber, the head having an internal drive for receiving a driving bit. In practice, the length of the unthreaded portion 10 plus the depth of the head 8 will correspond to the thickness of the timber to be fixed and which, in the case of decking, is normally produced in a standard thickness (or a range of standard thicknesses). A feature of the screw of the preferred embodiment is that the effective diameter of the drilling portion 2 is greater than that of the unthreaded portion 10 of the screw shank so that on application of the screw, the drilling portion 2 will drill through the timber being fixed a clearance hole for the unthreaded shank portion 10 which will extend through that clearance hole when the screw has been fully applied. This replicates the recommended practice of providing a clearance hole when pre-drilling timber decking for use with standard self-drilling wood screws. In practice, wood screws in accordance with the preferred embodiment of the invention are likely to be produced in a range of sizes from 8 gauge to 14 gauge and, depending on the actual gauge of the screw, the diameter of the drilling portion 2 will exceed that of the unthreaded shank portion 10 by 0.25mm to 1.5mm. It is envisaged that the majority of screws produced for fixing timber decking will be 10 gauge screws and for those, the diameter of the drilling portion 2 exceeds that of the unthreaded shank portion 10 by about 0.6 to 0.7mm. It will be seen from Figure 2 that when the drilling portion is viewed at 90° from the view of Figure 1 in other words from the "side" it has a reduced depth in relation to that which would be found in the drilling portion of a conventional self-drilling metal screw. This reduced depth results from displacement of material in the cylindrical wire blank during the forming process in creating the oversize drilling portion 2 (in terms of its effective drilling diameter).

As the oversize drilling portion 2 will also drill an oversize hole into the underlying timber structure into which the screw is driven, the screw thread must have a diameter sufficient to properly engage with the surrounding timber which means it will have a thread tip diameter somewhat larger than in a conventional screw of the same gauge. The thread is produced by displacement of material in the wire blank in a rolling process and for a given gauge of screw there is an inherent limit as to the amount of material which can be displaced from the wire blank to form the thread. In the preferred embodiment the increase in thread tip diameter is achieved by reducing the flank angle of the thread to an included angle β of from 15° to 45° (with about 30° being preferred), in contrast to a 60° included angle which would be typical in a conventional screw. As a result of this reduced flank angle there is increased material available to provide the required increased thread tip diameter. Within the range of sizes in which the screw of the preferred embodiment of the invention is likely to be produced (8 gauge to 14 gauge) the thread tip diameter will exceed the diameter of the drilling portion 2 by at least about 0.75mm, more typically by about 1.0 to 1.4mm. Due to the practical restrictions on the displacement of material used to form the thread it is unlikely that the thread tip diameter could exceed the diameter of the drilling portion by more than about 2.0 to 2.5mm within the gauge range indicated above without compromising excessively on thread pitch or thread root thickness, in one example of a 10 gauge screw having a thread with 16 TPI (turns per inch), the thread tip diameter of a screw of the preferred embodiment will be about 5.8 to 6.0mm whereas that in a conventional screw of that same gauge would be of the order of 4.65 to 4.8mm.

In the embodiment shown, the head of the screw is a countersunk head having teeth on its underside in order to cut a countersinking recess in the surface of the timber decking. It is however to be understood that screws within the broad scope of the invention are not confined to screws for fixing timber decking, and have a wide range of possible applications in the fixing of timber or other cladding to underlying timber support and the configuration of the head and the drive by which the screw is driven, can be modified to suit specific applications.

Although it is envisaged that the screw particularly described will be used primarily for fixing to an underlying timber structure, the screw is capable of being driven into underlying metal structure. The preferred embodiment of the screw as described would be capable of being driven into metal structure having a maximum thickness of 5.0mm, although a typical metal thickness with which the screw is likely to be used is 2.4mm.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not by way of limitation. It will be apparent to a person skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the present invention should not be limited by any of the above described exemplary embodiments.Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A screw for fixing timber to an underlyi ng ti mber or metal support, the screw comprising a shank having a drilling portion at one end and a head at the opposite end. the drilling portion having a drilling tip with cutting edges which lead into flutes that extend along the length of the drilling portion so as to define a constant effective diameter of the drilling portion, and a thread extending from the end of the drilling portion remote from the drilling tip to a position spaced from the head whereby the screw shank has an unthreaded portion between the end of the thread and the head, wherein the drilling portion is operative to drill during application of the screw a hole having a diameter greater than that of the unthreaded portion of the screw shank whereby when the screw is applied through the timber to be fixed there will be formed through that timber a clearance hole for the unthreaded shank portion.
2. A screw according to claim I, wherein the drilling portion has a diameter at least about 0.25mm greater than that of the unthreaded shank portion.
3. A screw according to claim 2. wherein the diameter of the drilling portion is up to about 1.5mm greater than that of the unthreaded shank portion.
4. A screw according to any one of claims 1 to 3, wherein the thread tip diameter is constant over at least a substantial part of its length and that diameter is at least about 0.75mm greater than that of the drilling portion,
5. A screw according to claim 4, wherein the thread tip diameter is about 1.0 to 1.4mm greater than that of the drilling portion.
6. A screw according to any one of claims ! to 5, wherein the profile of the thread provides an included angle of from 15 to 45° subtended between the opposed flanks of the thread.
7. A screw according to claim 6, wherein the included angle subtended between the opposing flanks of the thread is about 30°,