Patent Application
20110206478
This invention relates to camming elements for fasteners, and particularly, though not exclusively, to camming elements for fasteners for use in the furniture industry.
A known fastener for holding two members together is illustrated in
Rotation of the camming element 1 causes cam surfaces 8, 9 of the camming element to engage with the head 7 of the dowel 2 and further rotation of the camming element 1 pulls the head 7 of the dowel 2 further into the circular hole 5. This, combined with the attachment of the dowel 2 to the first member 3, causes the first member 3 to be pulled toward and fastened to the second member 4.
Rotation of the camming element 1 is effected by applying torque to a torque connecter 10, an example of which is a cross-head screw slot that allows the rotation and camming action of the camming element 1 to be driven using a standard screwdriver 11.
Conceptually, the camming element 1 can be thought of as roughly cylindrical, being formed of three coaxially arranged spaced discs. The first of these discs has an outer surface along part of the circumference of the cylinder for contacting the circular hole 5 in the second member 4. The disc is cut away to produce a first camming surface 8, which is to contact the head of the dowel 2. The second disc is shaped similarly to the first, and is positioned such that there is a slot 12 between the first and second discs. The third disc is positioned so that second disc is between the first and third discs. The third disc is not cut away, and has the torque connecter 10 at its centre. The third disc has the function of providing a covering for the circular hole 5. It should be noted that the phrase “cut away” is used to describe the shape of the camming element 1, and does not imply a particular method of manufacture.
In the field of camming fasteners, reduction of weight and materials is considered desirable. This is particularly true when the fasteners are made from expensive materials, such as zinc. In this case, a reduction in weight, or equivalently the amount of raw material required, can lead to a considerable reduction in cost. Weight can be reduced by coring. Coring is well known in the art and is a process of removing unnecessary material from a component. As is well known, the “removal” of material can take place at the design stage, and does not necessarily require physical removal of material. In relation to camming fasteners, it is known to perform coring from the first and second discs by removal of material from the faces between the first and second discs.
In the known camming fasteners, the camming element can tilt within the circular hole, leading to the first 3 and second 4 members becoming loose with respect to each other. This is undesirable, and can lead to a loose joint and failure of the fastener. For example, when the fasteners are used in the furniture industry, tilting of the camming element 1 can lead to wobbly furniture.
In known designs, it is possible for excessive torque to be applied via the torque connector 10, leading to damage or destruction of the camming element 1. In particular, the third disc, via which torque is applied, can shear off the second disc. In commercially available fasteners, it is possible for the camming element 1 to be damaged or destroyed by torques that can typically be applied manually with a standard screwdriver.
The present invention provides a camming element for a device for forming a joint between two members, the camming element comprising: a first engagement element having a first cylindrical outer surface, a first curved camming surface, and a first wall portion between the first outer surface and the first camming surface; a second engagement element having a second cylindrical outer surface, a second curved camming surface and a second wall portion formed between the second outer surface and the second camming surface, the second engagement element being axially spaced and coaxial with the first engagement element; and a slot between the first and second engagement elements; wherein a width of the first cylindrical outer surface in an axial direction is greater than a thickness of the first wall portion in the axial direction; the camming element being rotatably mountable, in use, in a hole in one of the members, the first and second camming surfaces being engageable, in use, with a head portion of a fastening element which is connectable, in use, to the other member, rotation of the camming element in a first direction serving, in use, to draw the members together by action of the first and second camming surfaces pulling on the head portion of the fastening element.
The invention also provides a camming element for a device for forming a joint between two members, the camming element comprising a first engagement element having a first cylindrical outer surface, a first curved camming surface, and a first wall portion between the first outer surface and the first camming surface; a second engagement element having a second cylindrical outer surface, a second curved camming surface and a second wall portion formed between the second outer surface and the second camming surface, the second engagement element being axially spaced and coaxial with the first engagement element; a slot between the first and second engagement elements; and wherein a face of the first wall portion facing away from the second engagement element is cored; the camming element being rotatably mountable, in use, in a hole in one of the members, the first and second camming surfaces being engageable, in use, with a head portion of a fastening element which is connectable, in use, to the other member, rotation of the camming element in a first direction serving, in use, to draw the members together by action of the first and second camming surfaces pulling on the head portion of the fastening element.
The invention further provides a camming element for a device for forming a joint between two members, the camming element comprising a first engagement element having a first cylindrical outer surface, a first curved camming surface, and a first wall portion between the first outer surface and the first camming surface a second engagement element having a second cylindrical outer surface, a second curved camming surface and a second wall portion formed between the second outer surface and the second camming surface, the second engagement element being axially spaced and coaxial with the first engagement element a slot between the first and second engagement elements; a torque coupling section for applying a torque parallel to the axis of the first and second cylindrical outer surfaces; wherein the torque coupling section is radially displaced from the rotational axis of the camming element; and a face of the second wall portion facing away from the slot and the second curved camming surface are exposed when viewed axially, the camming element being rotatably mountable, in use, in a hole in one of the members, the first and second camming surfaces being engageable, in use, with a head portion of a fastening element which is connectable, in use, to the other member, rotation of the camming element in a first direction serving, in use, to draw the members together by action of the first and second camming surfaces pulling on the head portion of the fastening element.
The invention further provides a camming element for a device for forming a joint between two members, the camming element comprising:
By way of example, embodiments of the invention will now be described with reference to the accompanying drawings, in which:
a is a perspective view of a first embodiment of a camming element according to the invention,
b is another perspective view of the first embodiment,
a is a perspective view of a second embodiment of a camming element according to the invention,
b is another perspective view of the second embodiment,
a is a perspective view of a third embodiment of a camming element according to the invention,
b is another perspective view of the third embodiment, and
a and 4b show a first embodiment. A camming element 1 according to this embodiment has first 15 and second 16 engagement elements, which form a pair of jaws. The outer surface of each of the first 15 and second 16 engagement elements (first outer surface 17 and second outer surface 18, respectively) is a cylindrical surface. As used herein, the term cylindrical surface describes a surface lying on the surface of a cylinder, but is does necessarily occupy the whole circumference of the cylinder. Preferably, the cylinder is right circular, or substantially right circular. Preferably, the surface of the cylinder is curved. In the present embodiment, the outer surface is convex.
The first 15 and second 16 engagement elements are coaxial and axially separated.
The first 15 and second 16 engagement elements have respective first 8 and second 9 camming surfaces, each of which is a curved surface adapted to contact the head 7 of a dowel 2. The camming surfaces 8, 9 may have ridges formed thereon, to grip the head 7 of the dowel 2. In the present embodiment the camming surfaces 8, 9 are inside the cylindrical surface, and face generally inwardly of the cylindrical surface, so as to be concave.
Between the first outer surface 17 and the first camming surface 8 is a first wall portion 19. The first wall portion is substantially transverse to the cylinder axis. The faces of the wall portion 19 may be perpendicular to the surface of the cylinder. Similarly, a second wall portion 20 is between the second outer surface 18 and the second camming surface 9.
Between the jaws formed by the first 15 and second 16 engagement elements is a slot 21. The slot 21 is intended to receive the neck of the dowel 2.
According to the present embodiment, the first outer surface 17 has a width, w, in an axial direction which is greater than the thickness, t, of the first wall portion 19 in the axial direction. Preferably, as in the present embodiment, the outer surface 17 extends beyond the first wall portion 19 in a direction parallel to the axial direction and away from the second engagement portion 16, as in this case the coring is easier to produce.
It has been discovered that the reason for the problematic tilting of the conventional camming element is a result of the hole 5 (into which the camming element is to be placed) meeting the bore 6 (in which the dowel 2 is placed). In use, the first outer surface of the cam 17 is braced against the inner surface of the hole 5, and the presence of the bore 6 effectively reduces the area against which the camming element can be braced. This can lead to the camming element digging into the side of the hole 5 and thereby tilting.
The above structure according to the embodiment leads to improved support for the camming element 1 when in use, because there is increased contact area between the first outer surface 17 and the side of the hole 5 in which the camming element rotates.
Furthermore, since the first wall portion 19 is thinner than the width w of the first outer surface 17, less material is required compared with the case where the wall 19 is the same thickness t as the width w of the outer surface 17. Therefore, the present embodiment allows a reduction in weight and raw materials.
As can be seen in
According to the present embodiment, the camming element 1 also has a disc-shaped top plate 22, contiguous with the second engagement element 16. The top plate 22 is preferably coaxial with the first 15 and second 16 engagement elements, and preferably has a radius substantially the same as the first 17 and second 18 cylindrical surfaces. The top plate 22 thus conceals the engagement elements 15, 16 when the cam is in use.
The top plate 22 is provided with a torque coupling section 10, which allows a torque to be applied to the camming element 1. The torque is applied so as to cause rotation of the camming element 1 about its axis. Therefore, the torque is directed along the axis of the camming element 1, since the torque is a vector quantity equal to the cross product of the radial vector (from the fulcrum to the point where a force is applied) and the force, and the direction of torque is given by a right hand grip rule.
The torque coupling section 10 is a depression that mates with the head of a screwdriver.
An example of a camming element 1 according to a second embodiment is shown in
In this case, the centre portion of the top plate 22 is not required to be so thick, as the torque coupling section 10 is now formed at an off-centre position where material interconnecting the top plate 22 and the second engagement element 16 is present. More particularly, the torque coupling section 10 is preferably located axially relative to a spine section 23. The spine section 23 extends substantially parallel to the axis and interconnects the top plate 22 and both of the engagement elements 15, 16.
It has been discovered that a camming element 1 according to the second embodiment has increased strength, and is less prone to shearing of the top plate 22 from the second engagement element 16. This increase in strength and resistance to breakage can be achieved, even though the amount of material connecting the top plate 22 to the second engagement element 16 is reduced, allowing a reduction in weight and cost. More particularly, the camming element 1 according to the second embodiment, when in use, does not rotate about the torque applied to the torque coupling section 10, but instead rotates about an axis parallel to the torque. Due to the resultant mechanical advantage, the applied torque necessary to install the camming member 1 is reduced, and this reduces shearing of the top plate 22.
A third embodiment is shown in
In removing the top plate 22, the camming element 1 overcomes a prejudice in the art, which teaches that the top plate 22 is necessary to conceal the engagement members 15, 16. A further prejudice in the art teaches that the top plate 22 is necessary to guide the camming element 1 when it is rotated in use. However, this is not the case.
According to the third embodiment, the absence of the top plate 22 means that the face 24 of the second wall portion facing away from the slot 21 and the second curved camming surface 9 are exposed when viewed axially. This dispensing with the top plate 22, leads to a considerable saving in material and cost. Furthermore, it has been found that the removal of the top plate 22 does not hinder the installation of the camming element 1, which can be guided sufficiently by the outer surfaces of the engagement elements 17, 18.
Although the camming element 1 of the third embodiment is described as similar to the camming element 1 of the second embodiment (which incorporates features of the first embodiment), the features concerning the absence of the top plate 22 and location of the torque coupling section 10 of the camming element 1 of the third embodiment could also be applied to a camming element 1 that does not have the coring described in the first embodiment 1. The torque coupling section 10 of this embodiment could be provided on a camming element 1 in which the jaws are not cored, or a camming element 1 that is cored between (inside) the jaws but not outside the jaws, or even a camming element 1 in which the width w of the first outer surface 17 is less than the thickness t of the first wall portion 19.
The embodiment shown in
The torque coupling section 10 is offset from the rotational axis of the element 1, as in the second and third embodiments. The element 1 has a top plate 22, as in the first and second embodiments. Here, however, the top plate 22 is slightly stepped down from the top surface of the element 1. The top surface of the element 1 is represented by the upper surface of the torque coupling section 10 and is designed to lie essentially flush with the surface of the board or panel in use. The slight stepping down of the top plate 22 in this embodiment has several advantages. Firstly, it makes the top plate 22 more closely integral with the second engaging element 16. This gives the structure added strength. It also means that the top plate 22 lies in closer proximity to the line of action of the forces that the element 1 will experience in use. These are the forces that arise between the first 15 and second 16 engaging elements and the head 7 of the dowel 2 when the joint is tightened. This gives the element 1 greater resistance to tilting in use. This is because the circumferential edge of the top plate 22 is more closely aligned with the forces on the element 1, giving it greater stability in its engagement with its mounting hole in the board or panel. This also helps to make a stronger joint.
The slight stepping down of the top plate 22 also facilitates the application of a cover cap (not shown) to conceal the element after the joint has been set.
Variations and Alternatives
The first 15 and second 16 engaging elements are not necessarily restricted to forming jaws, so long as they can achieve the function of camming the head 7 of a dowel 2. For example, the ends of the first 15 and second 16 engaging elements that are free in the disclosed embodiments could be connected to each other, with the slot 21 enlarged near these ends to admit the head 7 of the dowel 2.
The camming surfaces 8, 9 are described as curved. As used herein, curved is intended to include a substantially curved shape formed by a series of flat segments lying tangential to a curve.
The torque coupling section 10 is not particularly limited, and could be any section that would allow a torque to be applied to the camming member 1, and may include any combination of depressions or protrusions. Further examples include a slot for a flat-head screwdriver or a depression for a hex key.
The torque coupling section 1 could be integrally formed with the second engagement element 16, and need not protrude past the second engagement element 16 in the axial direction. The torque coupling section may extend past the second engagement element 16 to the first engagement element 15. For example, the torque coupling element 10 could include a hole for receiving a hex key, the hole passing the whole length of the camming element 1. In the second and third embodiments this hole could pass axially through the spine 23.
Preferably, the camming element 1 of the present invention is integrally formed, by a moulding process, for example. However, this is not essential, and other means of production, and non-integrally formed camming elements 1 are also within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0815236.5 | Aug 2008 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB09/01968 | 8/7/2009 | WO | 00 | 4/19/2011 |
