According to one aspect of the invention there is provided a fastening device for attaching one member to another, said device comprising an elongate fastening element having a first end insertable in a hole in one of the members and a second end insertable in a hole in the other member, a tightening element rotatably mounted in said other member with at least one camming surface engageable with the second end of the fastening element and operable to cause longitudinal movement of said fastening element along its axis in a first direction towards said tightening element upon rotation of said tightening element in a first sense, the device further comprising an expandable element at least partially surrounding the fastening element adjacent its first end and also insertable into said hole in said one member, the expandable element being designed to expand radially outwardly when subjected to an axially-directed clamping force, such a clamping force being applied to the expandable element between the first end of the fastening element and a reaction point towards its second end when said longitudinal movement of the fastening element is caused by said rotation of the tightening element.

In another aspect, the invention provides a fastening device comprising a sleeve element having a hole extending therethrough, an elongate dowel element located in said hole, camming means cooperating between said sleeve and dowel elements to cause relative longitudinal movement between the two elements when the dowel element is rotated about its longitudinal axis relative to the sleeve element, and expanding means cooperating between said sleeve and dowel elements to cause outward expansion of at least a part of the sleeve element upon said relative longitudinal movement between the two elements.

By way of example, embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a part-sectional view of a device according to one aspect of the invention, Figure 2 is a part-sectional view of the device of Figure 1 in its tightened condition, Figure 3 is a detail view of one end of the pin from the device of Figure 1, Figure 4 is a detail view of an alternative form of expandable element from the device of Figure 1, Figure 5 is a sectional view of a fastening device according to another aspect of the invention, Figure 6 is a view showing the features of the sleeve element, Figure 7 is a view of the dowel element, Figures 8a and 8b are part-sectional views showing the fastening device in use in one typical application, and

Figures 9a and 9b are part-sectional views showing the fastening device in another typical application.

A fastening device 10 is seen in Figure 1. The device 10 is for fastening one member 11, which in this case is a panel, to another member 12, which in this case is a tubular element. The device 10 comprises an elongate pin 13 of circular cross-section, one end 14 of which is insertable into a hole 15 in the tubular element 12. At its other end, the pin 13 has a head 16 which is designed to be engagable with a cam 17 rotatably mounted in a hole 18 in the panel 11. The shank 19 of the pin 13 extends through a hole 20 in the panel 11.

In known fashion, the cam 17 has a pair of arcuate camming surfaces 21 which engage the head 16 of the pin 13 and which, upon rotation of the cam in the sense of arrow A, eg by a screwdriver, cause longitudinal movement of the pin along its axis towards the cam in the direction of arrow B.

At its end 14, the pin 13 has a boss 22. The boss 22 is round-nosed to facilitate its insertion into the hole 15 in member 12. As will be seen more clearly in Figure 3, the boss 22 is generally mushroom-shaped and incorporates a hole 24 that extends through the shank 19 of the pin 13. The boss 22 has cutaway slots 25 on either side in the region of the hole 24. The pin 13 is conveniently made of cast zinc.

The pin 13 is fitted with an expandable element 26 at its end 14 next to the boss 22. The expandable element 26 is of a resiliently deformable material such as rubber and is conveniently fitted to the pin 13 by moulding. In this process, the rubber material fills the cutaway slots 25 and hole 24 in the boss 22 of the pin 13. This helps to keep the expandable element 26 in position and prevent it from creeping under compression.

On the other side of the expandable element 26, towards the head of the pin 13, the pin is fitted with a sleeve 27. The sleeve 27 is of a relatively stiffer material than the resiliently deformable element 26, such as plastics, and is again conveniently fitted to the pin by moulding. The expandable element 26 and sleeve 27 can be fitted by a process known as multi-shot insert moulding.

The sleeve 27 extends between the expandable element 26 and the outer surface of the cam 17.

Turning to Figure 2, it can be seen here that the cam 17 has been rotated fully round in the direction of arrow A. This in turn has caused the end 14 of the pin 13 to move nearer the cam 17 in the direction of arrow B. This longitudinal movement of the pin 13 creates an axially-directed clamping force on the expandable element 26 between the boss 22 of the pin 13 and the adjacent end of the sleeve 27, with the other end of the sleeve reacting against the outer surface of the cam 17. This axially-directed clamping force causes the expandable element 26 to expand radially outwardly. In its expanded condition, the expandable element 26 is able to grip the tubular element 12 and there is sufficient travel in the cam 17 for the tubular element than to be pulled tightly against the panel 11, creating a joint between the two.

Figure 4 illustrates a modified form of expandable element 26'. Here the expandable element 26'incorporates a couple of circumferential grooves 27.

The aim of this design is to promote the radial expansion characteristics of the expandable element under the axially-directed clamping force. Other designs for achieving this aim will be readily apparent. It may be possible, for example, to form the sleeve and expandable element out of a single integral piece of material, with the expandable part being defined by a reduced- material section. It may also be possible to form the sleeve and expandable element out of different materials in a single moulding process.

Further modifications are possible. For example, the sleeve could be arranged to react against some surface other than the outer surface of the cam 17, such as the face of the panel 11. In fact, it may even be possible to dispense with the sleeve altogether and have the expandable element abutting directly against the outer surface of the cam 17 or the face of the panel 11 as a reaction point for the clamping force.

A fastening device of the nature described above has a number of advantages. An important one is that it is only necessary to prepare one hole in the tubular member, and that hole need not be finished off. Another is that the finished joint is invisible, save for the face of the cam in its hole in the panel. A further advantage is that by the nature of the expandable element, the fastening device is able to tolerate an appreciable amount of inaccuracy in the dimensioning and positioning of the mounting holes and still provide a tight joint.

A fastening device of the nature described above is also suitable for use in other applications, such as where one panel is to be attached edge-on to the face of another panel. In such a case, the expandable element would expand into a blind hole in the face panel. It has been found that this provides a tight joint, with a high degree of resistance to"pull out". It is thought that this is because the elastomeric material of which the expandable element is formed is able to"flow"to a certain extent when it is expanded into its hole which, with panels made of a relatively coarse material such as chipboard, provides an effective anchorage.

The fastening device described herein is releasable, simply by rotating the cam 17 in the opposite sense to arrow A. This releases the compression on the expandable element, allowing it to return to its original state, as shown in Figure 1, at which point the pin can be removed from its hole in the tubular member 12 and the two parts separated.

It will be understood that the fastening device described above with its expandable element could be designed to work equally well with a so-called "drop-on"type of fitting, as well as the"push-in"type of fitting described. In the"push-in"type of fitting described, the fastening element is inserted axially into holes in both members to be joined and its longitudinal movement is caused by rotation of the cam. In the"drop-on"type of fitting, instead of a rotatable cam there is a bifurcated ramp and the longitudinal movement of the fastening element is caused by its lateral movement on this ramp.

The fastening device shown in Figure 5 comprises a sleeve element 110 and a dowel element 111. The sleeve element 110 of a resiliently deformable material such as plastics. The dowel element 111 is of a material such as zinc and is conveniently made by casting. The sleeve element is conveniently formed around the dowel element by a process known in the art as insert moulding, ie it is moulded directly onto the dowel element.

The sleeve element 110 has a hole 112 extending therethrough in which the dowel element 111 is located. Here the sleeve element 110 is stepped in its outer diameter, with one section 113a being of smaller dimension than the other section 113b, and the junction between these two sections thereby defining an annular shoulder 121. The smaller diameter section 113a is designed to be outwardly expandable when subjected to an axially directed clamping force. The sleeve element 110 is conveniently formed as a single integral piece, though this is not essential.

At one end, the dowel element 111 has a head 114. The head 114 is provided with a feature such as slot 115 to be engagable by a screwdriver to enable the dowel element to be rotated about its longitudinal axis 116. The head 14 also has a camming surface 117. The camming surface 117 here extends in a generally helical or spiral path around the longitudinal axis 116 of the dowel element 111 (as seen better in Figure 7). The sleeve element 110 here also has a camming surface 118 which extends in a generally helical or spiral path (as seen better in Figure 6) so as to complementarily engage the camming surface 117 of the dowel element 111. It will be understood that with this arrangement, when the dowel element 111 is rotated in a certain direction relative to the sleeve element 110, the dowel element will be caused to move longitudinally relative to the dowel element by the action of its camming surface 117 riding up the camming surface 118 of the sleeve element. Here, a clockwise rotation of the dowel element 111 (when viewed from on top in Figures 5, 6 and 7) will cause movement of the dowel element relative to the sleeve element in the direction of arrow A.

At its other end, the dowel element 111 has an abutment 119. The abutment 119 is arranged to engage the sleeve element 110 at the end of its smaller diameter section 113a. It will be understood that with this arrangement, when the dowel element 111 is rotated as just described, its abutment 119 will be drawn in the direction of arrow A. With the two camming surfaces 117 and 118 of the dowel and sleeve elements engaging

one other, this means that the sleeve element 110 will effectively be subjected to an axially directed clamping force. As noted above, this axially directed clamping force will cause the smaller diameter section 113a of the sleeve element to expand outwardly, because of the nature of the material of which it consists.

The sleeve element 110 will tend to expand outwardly at its smaller diameter section 113a rather than at its larger diameter section 113b, because the former is of thinner-walled section than the latter. The sleeve element can therefore conveniently be made from material having a constant degree of resilient deformability throughout. If desired, however, it would be possible instead or in addition to form the expandable and non-expandable parts of the sleeve element out of material with different degrees of resilient deformability. The sleeve element could be formed in two different parts for this purpose, or it may be formed in a single process with different material characteristics.

Turning to Figures 8a and 8b, this shows an example of how the fastening device can be used in practice to join two members together. Here, one of the members 50 is a flat panel and the other member 51 is a tubular frame element. The frame element 51 is drilled through to receive the fastening device. In particular, hole 52 is a clearance hole through which the smaller diameter section 113a of the fastening device is designed to protrude,

whilst hole 53 is a clearance hole to allow passage of the head 114 of the device. The device is inserted into the frame element 51 until the annular shoulder 121 on the head 114 of the device comes into abutment with the inner surface of the frame element 51. A blind hole 54 in the panel 50 is designed to receive the protruding smaller diameter section 113a of the device when the two members are brought together, and this is the position seen in Figure 8a. The dowel element 111 is then rotated in a clockwise direction relative to the sleeve element 110, as described above, to cause outward expansion of the smaller diameter end 113a, which then becomes effectively anchored in the hole 54 in the panel 50. This is the position seen in Figure 8b.

Further rotation of the dowel element 111 in the clockwise direction will tend to pull the panel 50 towards the frame element 51 and thus create a tight joint between the two.

The joint is releasable, simply by rotating the dowel element 111 in a counter-clockwise direction. With the axial clamping force on it now released, the smaller diameter section 113a of the sleeve element 110 can return to its original configuration seen in Figure 8a, at which point the panel 50 and frame element 51 can be separated.

The device described is able to work effectively without necessarily needing the holes in the frame element 51 to be"finished off'. The resulting joint is aesthetically pleasing too, in that the head 114 of the device is hidden

within the frame element 51 and all that is normally visible, therefore, is the clearance hole 53. Where the panel 50 is of a material such as chipboard, it has been found that an expandable elastomeric sleeve such as that described can provide a very effective anchorage with a high degree of resistance to pull-out.

Figures 9a and 9b show a possible alternative arrangement, which is essentially the reverse of that shown in Figures 8a and 8b. Here it is the panel member 60 that is drilled through, with a clearance hole 61 for the smaller diameter end section 113a of the device and a counterbored clearance hole 62 of larger diameter for the head 114 of the device. The device is inserted until its annular shoulder 121 comes into abutment within the step 63 between the two different diameter holes 61 and 62 in the panel. The smaller diameter section 113a of the device protrudes and is designed to be received in a hole 64 in the frame element 65, as seen in Figure 9a. Rotation of the dowel element 111 in the clockwise direction relative to the sleeve element 110, as described above, causes outward expansion of the smaller diameter section 113a within the frame element 65 and further clockwise rotation will tend to pull the panel and frame element together. This is the position seen in Figure 9b.

The joint is releasable, as before simply by rotating the dowel element in a counterclockwise direction. Again the joint is aesthetically pleasing, with

the head 114 of the device being essentially hidden in the counterbore 62 in the panel 60, and there is no necessity for the hole 64 in the frame element 65 to be finished off.

Here, the camming surface 117 of the dowel element presents a single spirally or helically extending ramp. There is scope for up to about 270° of rotation of the dowel element relative to the sleeve element and this would normally be designed to produce around 2 to 3mm of relative axial movement.

It will be appreciated that other mechanisms could be used to provide an expandable region of the sleeve, element. For example, the end of the dowel element may be formed with a conical section which will react with the end section of the sleeve element when the two are moved longitudinally relative to each other to produce a radially outwardly directed expansion of the sleeve element in that region.

The spirally or helically directed camming surface of the dowel element is arranged here to give a constant rate of relative longitudinal movement between the two elements per degree of relative rotational movement, what might be called a"linear"action. It would of course be possible to design the camming surface differently to give a variable action instead, ie a variable movement/rotation ratio.

It has been found in practice that when the fastening device has been set by rotation of the dowel element in the tightening sense to expand the sleeve element, enough frictional forces exist to prevent the dowel element from rotating in the opposite sense and causing the joint to slacken off. It would be possible, however, to include a feature to help guard against such a possibility of slackening off, for example in the form of ratchet-like formations between the two inter-engaging camming surfaces.

It will be appreciated that other configurations of camming surfaces could be used for the sleeve and dowel elements other than the interengaging helical or spiral surfaces described. For example, these could be in the form of multiple or double wedges, like a dog clutch. Alternatively, the dowel element could be formed with a screw-threaded section, with a portion of the sleeve element formed therearound. In this case, there would be the possibility of one or more turns of rotational movement of the dowel element relative to the sleeve element.

It will be appreciated that the fastening device can be used in a number of different configurations and for joining together other members, eg, panel to panel, tube to panel, etc. The device is particularly advantageous for joining panels to tubular sections, however, because only a single hole is needed in the tubular member and the device remains mostly hidden. Furthermore,

there is sufficient"give"in the expandable section of the sleeve element for the joint to work without the need to"finish off'the hole in the tubular member. Normally, when connecting panels to tubular sections, it is necessary to"finish off'holes in the tubular section after drilling to remove the swarf from around the edge of the hole.