The present invention represents improvements and modifications over the abrasive disc and backing plate described in publication number WO 98/53955, which is hereby incorporated herein in its entirety where appropriate.

BACKGROUND OF THE INVENTION Conventional grinding discs, or disks, consist of a generally circular disc with a small central aperture. This aperture is merely provided for a spindle of the driving machine to protrude through. A locking member is screwed to the spindle to clamp the disc about the aperture to secure the disc in place.

One disadvantage of such a conventional system is the time taken to replace a disc. Replacing a disc requires unscrewing and rescrewing of the locking member.

Another disadvantage of the conventional disc is their inefficient use of materials. This arises from the fact that, in use, only an outer portion of the disc contacts a work piece. The inner portion is thus effectively wasted.

An attempt at overcoming some of the above disadvantages is the use of VELCRO (Trade Mark), or the like, to attach the disc to the backing disc. This facilitates faster replacement of discs. However, the limited strength of VELCRO (Trade Mark) restricts its application to low speed or low torque abrasion. Certainly, the grinding of metals is not within the capabilities of such a system.

A further attempt to overcome these advantages is described in WO 98/53955. This describes the provision of projecting tabs from the centre of an annular disc having an inner and outer periphery.

While this method seems to solve the problem of wasted materials at the centre of the abrasive disc, the engagement of the abrasive disc to the backing disc lacked security.

OBJECT OF THE INVENTION It is an object of the present invention to alleviate or overcome the aforementioned disadvantages of prior art devices or at least to provide the public with a useful choice.

Other objects of the invention may become apparent from the following description, which is given by way of example only.

SUMMARY OF THE INVENTION According to one aspect of the present invention, there is provided a grinding disc including: * an annular disc portion having an inner periphery and an outer periphery defining therebetween an abrasive surface; and at least two projecting portions provided on the disc portion for engagement, in use, with a supporting backing disc; wherein the at least two projecting portions are adjacent or substantially adjacent to the inner periphery of the disc portion.

Preferably, the projecting portions are tabs integral with the disc portion.

Preferably, the tabs are defined by a first line of weakening or severed line in the annular disc portion extending from the inner periphery outwards and a second line of weakening or a severed line intersecting said first line at its outer end and extending substantially transverse to the first line of weakening or severed line.

Preferably, the second line of weakening or severed line lies substantially on an arc of a circle concentric with said inner periphery and said outer periphery.

Preferably, the grinding disc includes at least four tabs located in adjacent pairs, wherein each tab is shaped to substantially oppose its adjacent tab.

According to another aspect of the present invention, there is provided a backing disc assembly for a grinding disc having an inner and outer periphery, the backing disc assembly including: * a backing disc adapted to support the grinding disc; and * a clamping means adapted to engage with the backing disk and the grinding disc; wherein in use, at least a portion of the grinding disc is disposed between respective engagement portions of the clamping means and backing disc.

Preferably, the clamping means and backing disc each include a plurality of engagement portions, each engagement portion including at least one surface adapted to frictionally engage a corresponding projecting portion of the grinding disc therebetween.

Preferably, the or each surface is substantially planar and is angled at a predetermined angle relative to the plane of the backing disc so as to be substantially parallel to the required angle of the corresponding projecting portion of the grinding disc.

Preferably, each planar surface is adapted to engage a tab of the grinding disc.

Preferably, the clamping means includes at least one protrusion adapted to be received by a slot or aperture in the backing disc to engage the clamping means with the backing disc, wherein in use, the protrusion extends through a corresponding slot or aperture in the grinding disc.

Preferably, the backing disc assembly includes a reinforcing

means including at least a partial ring of thickened material defining a step against which the inner periphery of the grinding disc abuts in use.

Preferably, an outer periphery of the clamping means is adapted to abut an inner periphery of the reinforcing means.

Preferably, the reinforcing means has chamfered edges.

Preferably, the backing disc includes a substantially rigid central disc and a substantially flexible outer disc.

Preferably, the outer disc is constructed from an elastomer, flexible plastic, rubber or nylon.

Other aspects of the invention may become apparent from the following description which is given by way of example only and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: Shows an exploded perspective view of a grinding disc and backing disc assembly according to one aspect of the present invention.

Figure 2: Shows a plan perspective view of an assemble backing disc assembly of Figure 1 with a grinding disc attached.

Figure 3: Shows a bottom perspective view of an assembled grinding disc assembly of Figure 1.

Figure 4: Shows a bottom perspective view of the backing disc hub of the backing disc assembly.

Figure 5: Shows a bottom perspective view of clamping cross 2 of the backing disc assembly.

Figure 6: Shows a plan perspective view of the combined backing disc and backing disc hub 13.

Figure 7: Shows a cross-sectional view along line A-A in Figure 6.

Figure 8: Shows a cross-sectional view along line B-B in Figure 6.

Figure 9: Shows a plan representation of a grinding disc according to a second aspect of the present invention.

Figure 10: Shows a schematic representation of the grinding disc shown in Figure 9 secured to a second embodiment of a clamping cross.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Throughout the accompanying drawings, equivalent portions or components are referenced by like numerals.

Figure 1 shows an exploded view of a grinding disc assembly 1 according to one embodiment of the present invention. The grinding disc assembly 1 includes a grinding disc 6 and backing disc assembly including a clamping cross 2, backing disc 10 and backing disc hub 13. All components in the grinding disc assembly 2,6,10 and 13 are concentric for use with a circular sander or grinder.

The grinding disc 6 consists of a flat surface with grinding particles embedded in it or having any coating known in the art for use in grinding or frictional treatment of surfaces. The grinding disc 6 is, typically, formed from conventional grinding paper, fibre or card.

Suitable materials will be apparent to those skilled in the art.

The grinding disc 6 has a circular portion removed from its centre. The area of the centre portion may be approximately equal to about one third of the total area defined by the periphery of the grinding disc 6 in the case of one preferred embodiment. Typically however, the diameter of the cut-out portion is 5 cm or more. In most

cases the area of the cut-out is more than one fifth of the total area defined by the outside periphery of the disc. The suitable size of the centre portion may be determined by the portion of a conventional disc which has only limite, or occasional, contact with a work piece when in use and also by the minimum width required to secure the grinding disc 6 to the backing disc assembly. Any region of a grinding disc 6 which would not contact the work piece would be essentially wasted.

The cut-out portion may be used separately to form a smaller conventional grinding disc.

The grinding disc 6 has at least two projecting engagement portions 7, which may be formed by severing the grinding disc 6 along line 20 or providing lines of weakening to be severed upon use of the grinding disc 6. The engagement portions may include tabs 8, which are bent or folded to protrude out of the plane of the grinding disc 6 for engagement with the backing disc assembly. An aperture 9 is thereby formed as a result of the bending of the tabs 8.

The line 20 to be severed preferably forms an arc of a circle concentric to grinding disc 6. Figure 1 shows a grinding disc 6 with four engagement portions 7, although any suitable number may be used. In the preferred embodiment shown in Figure 1, each engagement portion 7 includes two opposing tabs 8 located on opposing sides of the notch or aperture 9.

The clamping cross 2 includes engagement portions 3, which preferably correspond to the engagement portions 7 of the grinding disc 6. Engagement portions 3 include a protrusion or nub 4 adapted to be received by a receptacle 33 of the backing disc assembly to secure the clamping cross to the backing disc hub 13 and backing disc 10. The grinding disc 6 is oriented relative to the clamping cross 2 in use so that each nub 4 extends through a corresponding aperture 9.

Engagement portions 3 further include at least one substantially planar surface 32, preferably angled downwards and away from nub 4. The angle of the surface 32 is suitably commensurate with the required angle that tabs 8 are to extend from the plane of grinding disc 6 in use. This is so as to provide, in combination with a corresponding

substantially planar surface 15 on the backing disc hub 13, a frictional engagement with the grinding disc 6. The frictional engagement of the grinding disc 6 requires that the engagement portion to be placed adjacent or near to the inner periphery of the grinding disc 6. This is to maintain flexibility in the outer portions of the grinding disc 6 in use.

It will be appreciated that the surfaces 15,32 may be varied from planar. Variations may be used to increase the frictional engagement of the tabs 8. While clamping of the grinding disc 6 is preferable, operation may still be possible without clamping (by simply providing an aperture between surfaces 15,32 to receive tab 8. However, more reliable operation is expected by clamping the grinding disc 6 into place.

The clamping cross 2 further includes an aperture 5 for engagement with a shaft of a grinding machine (not shown). The clamping cross 2 may be made from any resilient material that will retain its shape while rotated at high speeds and may, for example be made from a metal, metal alloy or appropriate resilient plastic material.

In a preferred embodiment, the clamping cross 2 is constructed from aluminium.

The backing disc 10 includes an channel or groove 22 adapted to receive an end 30 (see Figure 5) of nub 4, thereby assisting to prevent relative rotation movement between the backing disc 10 and clamping cross 2. The backing disc 10 includes engagement portions 12 adapted to abut the ends 1 5A of planar surface 15, preventing relative rotation of the backing disc 10 and backing disc hub 13.

The backing disc 10 further includes reinforcing ribs 1 1 near its inner periphery. The outer diameter of reinforcing 11 is substantially equivalent to the inner diameter of the grinding disc 6 and the height of the reinforcing 11 above the plane of backing disc 10 is substantially equivalent to the height of the grinding disc 6. The reinforcing rib 11 aligns the grinding disc 6 and prevents air pressure building below the grinding disc 6, reducing the pressure applied to the tabs 8.

The reinforcing ribs 11 are constructed from a resilient material, for example a metal or resilient plastics material. The shape and dimensions of the reinforcing ribs 11 are such as to prevent catching on a work surface should accidental contact with the work surface occur. The edges of the reinforcing ribs 11 are chamfered to prevent catching.

In an alternative embodiment, the reinforcing ribs may be located on the clamping cross 2. However, it is the preferred embodiment that the reinforcing ribs 11 form part of the backing disc 10.

The backing disc 10 is preferably made from a flexible material such as an elastomer. However, it will be appreciated that any other flexible material could be used including a plastic, rubber or nylon. The backing disc 10 is moulded or otherwise formed around backing disc 13 by methods apparent to those skilled in the art, thereby resulting in a substantially rigid inner portion and substantially flexible outer portion. Rubber has the advantage of resulting in a high surface friction with the grinding disc 6, assisting to prevent slipping of the grinding disc 6.

The backing disc hub 13 includes planar surfaces 15 complementary to planar surfaces 32 for frictionally engaging the grinding disc therebetween. An aperture 16 is provided to receive a drive shaft and is preferably the same diameter as aperture 5. Backing disc hub 13 may further include a recessed portion 18 to receive a raised portion 19 (obscured) of clamping cross 2.

Figure 2 shows a perspective plan view of an assemble grinding disc assembly 1. The reinforcing ribs 11 are disposed immediately adjacent to the inner diameter of grinding disc 6. The upper surface of the reinforcing ribs 11 is in the same plane as the upper surface of grinding disc 6 so as to provide a substantially planar lower working surface.

Figure 3 shows a perspective bottom view of the grinding disc assembly 1 shown in Figure 2. The backing disc 10 substantially

covers the backing disc hub 13 up to a rim 17. Nubs 4 protrude through aperture (14) (obscured) of the backing disc hub 13 and into aperture 33 of the backing disk 10, preventing relative movement between the clamping cross 2, backing disc 10 and backing disc hub 13.

Figure 4 shows a bottom view of the backing disc hub 13. The backing disc hub 13 may be constructed from any suitably rigid material that will retain its shape while rotated at high speed, for example be made from a metal, metal alloy or appropriate plastic material. In a preferred embodiment, backing disc hub 13 is constructed from aluminium.

Figure 5 shows a bottom perspective view of clamping cross 2.

The perimeter 34 of clamping cross 2 is preferably at a diameter substantially equivalent to the inner diameter of reinforcing 11 so that reinforcing ribs 11 abut clamping cross 2 when the backing disc assembly is assemble. This prevents inwards radial deformation of backing disc 10 and therefore prevents deformation of the grinding disc 6. A raised portion or boss 19 may be provided to fit into the recessed portion 18 of the backing disc hub 13. It will be appreciated that raised portion 19 and recessed portion 18 may be any shape and could, for example be square. For any embodiment other than a circle, portions 18 and 19 may assist in the prevention of relative rotation between the clamping cross 2 and backing disc hub 13.

Figure 6 shows a perspective view of the backing disc 10 and the backing disc hub 13. Backing disc 10 may be formed around backing disc hub 13, for example by supporting backing disc hub 13 in a mould and applying rubber to the mould and allowing the rubber to set to form backing disc 10. In this way, backing disc hub 13 is effectively part of backing disc 10, which then has a substantially rigid centre and a substantially flexible outer periphery.

Figure 7 shows a sectional view along line A-A in Figure 6. The reinforcing ribs 1 1 may be integrally formed with backing disc 10 and comprise a partial ring of thickened material around the inner periphery

of backing disc 10. Alternatively, reinforcing 11 may be formed separately from backing disc 10 any may be produced in a different material from backing disc 10, for example aluminium. Another option may be to include reinforcing 11 as part of backing disc hub 13, either integrally or as a discrete component.

Figure 8 shows a sectional view along line B-B in Figure 6, further illustrating how in a preferred embodiment backing disc 10 and backing disc hub 13 fit together.

Figure 9 shows an alternative embodiment of a grinding disc 60 according to the present invention. In this embodiment, the protrusions 80 of the disc are formed by folded corners around the inner periphery of the disc. The clamping cross 20 fits into the apertures 90 in a similar manner to the embodiment shown in Figure 1.

It will be appreciated that the protrusions 80 may be folded to a plane substantially parallel to the planar surfaces of the clamping cross and backing plate or backing plate hub so as to frictionally engage the protrusions 80 of the grinding disc 60.

Figure 10 shows a clamping cross 200 engaged with grinding disc 60. Camping cross 200 in this embodiment may include engagement portions 61 which are commensurate with the fold line of the protrusions 80. Camping cross 200 may include a number of protrusions and engagement surfaces similar to nubs 4 and surfaces 32 of clamping cross 2. It will be appreciated that protrusions 80 may be formed on one or both sides of slot or aperture 90.

Suitable methods of connecting the backing disc to a grinding or sanding machine will be apparent to those skilled in the art. The preferred embodiments of the present invention employ a conventional spigot type attachment of the backing disc by way of the aperture 21 to a grinding or sanding machine.

Where in the foregoing description reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if

individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made thereto without departing from the scope of the appended claims.