Background of the Invention

The present invention relates to an abrading element for abrading machines for use in surface finishing, to an abrading head for a machine incorporating such elements, and to a machine having an abrading head with such elements. A wide variety of machines exist for abrading of surfaces as part of a surface finishing process, with constructions and dimensions adapted to the task in hand. These generally comprise a main machine body and some kind of abrading head or abrading surface which is movable in rotary or oscillatory manner relative to the machine body, on which there is held an abrasive material such as a sandpaper or the like. The abrasive material is liable to become worn out with use and need regular replacement, and for this reason it is usual that the abrasive material be held in releasable manner on the abrading head.

A construction of abrasive material which is utilised in particular in machines for the finishing of objects of non-planar form and with particular applicability in the woodworking industry employs a plurality of elongate abrading elements of composite form where each includes a sandpaper or sandpaper-like member or series of such members secured only at an edge and which lie on their opposite non-abrasive faces against a resilient brush -like support. More particularly, the sandpaper may be in the form of a long strip which is held along a long edge, and is cut with a series of lateral cuts which extend part-way or even fully across the strip to form what is effectively a series of individual strips or lamellae. As the head to which the element is secured rotates and is pressed against a workpiece the individual strips will deform towards and be supported by the resilient support. The resilience of this resilient support, and to an extent the resilience of the sanding strip, will dictate the abrading pressure which is applied. The provision of what is effectively a series of individual sanding strips means that the abrading elements can readily conform to a non-planar surface without the tendency to create flattening of convex surfaces, and still allowing access to concave surfaces. Such a composite abrading element structure is well-known both for abrading heads of disc-like generally planar form where the abrading strips are held along their edges in radially-extending manner on the head protruding downwardly from the head, as well as for machine structures where the abrading elements are fitted on the outer periphery of a cylindrical drum extending axially or in a helical manner, and where a pair of such drums may be arranged adjacent and counter-rotating to each other.

In such machines the abrading heads or drums are provided with slots or recesses therein of undercut form, where the abrading elements have an elongate base part of shape adapted to be received within this undercut recess, which can be slid lengthwise into and out of the slots or recesses. Such a structure is able to tightly hold the abrading elements onto the heads. In the case of a cylindrical drum construction the drum rotation itself is then able to assist in the retention in that the centrifugal force which acts radially outwardly on the abrading elements tends to urge the dovetail base into more tight engagement in the slots.

Various specific constructions are utilised for these composite abrading elements. A conventional structure employs a profile body of dovetail section within which is held a brush-like supporting member comprising a large number of bristles and where an abrasive sheet is secured along an edge the these bristles. Such a structure is disclosed in EP 1272312B.

It is also known to use a main profile body in combination with a U-shaped retaining profile where the U-shaped profile serves to releasably retain the main profile body and abrading material in the machine head recess. In WO

2007/009466 the U-shaped profile serves to grip the abrasive material in a releasable manner, sandwiching it between this U-shaped profile and the main profile body.

The present invention is directed to providing an improved structure of abrading element, and to machine heads and to a machine employing such abrading elements.

The invention has particular applicability in connection with the finishing of wind turbine blades, which have enormous surface area of non-planar and

continuously-changing form which must be carefully preserved during finishing, and where large quantities of abrading materials are consumed. However, the invention is not restricted to this application, but has broader applicability.

Summary of the Invention

In a first aspect the invention resides in an abrading element for use in an abrading machine having an abrading head, comprising a support member having a mounting portion which defines a profile portion for receipt, in use, in a slot or recess within an abrading head, and a support portion extending from the mounting portion, and an abrasive material secured to the support portion, wherein the support portion is formed of resilient material and is adapted to deform as the element is urged against a workpiece.

In a preferred form the support portion comprises a blade-like body, which depending on the degree of required flexibility may be provided with a series of spaced slits defining individual resilient elements. The mounting portion and the support portion may advantageously be monolithically formed, for example by extrusion. They may also be formed by a co-extrusion allowing the use of different materials; for example it may be arranged that the material of the support portion is softer than that of the mounting portion, whereby the mounting portion exhibits higher rigidity, useful for firm retention on the head, and the support portion a greater degree of resilience or flexibility.

The support portion may be configured to be of tapered sectional form narrowing away from the mounting portion , whereby a high degree of flexibility is obtained at the distal edge supporting the abrasive element or elements where these directly contact the workpiece.

The mounting portion may comprise a block of dove-tail section or other section according to the shape of the slot or recess in the machine head, which block may be of hollow form to reduce the material requirement and reduce weight.

The abrasive material may comprise one or more abrasive sheets which may be secured in the region of a proximal edge of the support portion adjacent the mounting portion. Alternatively, the abrasive sheet or sheets may be secured in the region of a distal edge of the support portion distant from the mounting portion, or at an intermediate position. Where the support portion is formed with a series of slits defining individual elements, individual abrasive sheets may be secured to the individual elements.

The abrasive sheet or sheets may be secured by a variety of techniques. A particularly preferred technique has the sheets sewn on to the support portion by stitching. This affords a very reliable yet flexible connection. Other techniques employ an adhesive, or staples of a welding process. Various combinations of securing techniques may be used.

A foam pad may be arranged between the abrasive sheet and the support portion, in order to absorb a degree of the abrading force, and to even out the distribution of force which is applied. The abrasive material may alternatively comprise abrasive particles secured at least to a distal region of the support portion distant from the mounting portion. The support portion may have at its distal edge an edge region of enlarged section at which these abrasive particles are provided, embedded in this enlarged edge region. This enlarged edge region may be formed as an extrusion of a plastics material with the abrasive particles distributed within the plastics material, or they may be provided as a coating.

In an alternative construction the abrading element may comprise a sheet of thin material bent or otherwise formed to define the mounting portion and support portion, such as a sheet of springy material such as steel, or a composite material, or a plastics material. The sheet of thin material may be formed to have a channel-like portion which constitutes the mounting portion, for example, bent or formed to have a portion of hollow dovetail section. The support portion at a position distant from the mounting portion may be bent or otherwise formed to have a nose region at which the abrading element when in use engages a workpiece. The abrasive material may be a sandpaper type material or may be an abrasive grit secured to the resilient portion at least in the nose region, for example by an adhesive or binder, or by another technique such as an

electroplating technique. A particularly effective form of abrasive is a diamond grit secured by electroplating.

This form of abrading element lends itself to provision as a multi-element structure, where the structure has a plurality of mounting portions each fitting in a respective slot or groove in the machine head, with bent nose-defining support portions interconnecting the mounting portions. The structure may be pre-bent whereby the nose regions are defined prior to fitting on a machine head.

Alternatively, it may be arranged that the support portions between a pair of mounting portions are configured to be generally planar prior to fitting on a machine head, adopting the bent shape having the nose regions when fitted to a machine head, whereby the nose regions are in a state of compression. According to a further aspect the invention provides an abrading element for use in an abrading head of an abrading machine, comprising: an elongate body from which protrude one or more resilient elements, said body comprising a profile body for receipt in a slot or recess within the abrading head; a support member of generally U-shaped form which surrounds the profile body having an extension portion which in use protrudes from the slot or recess; and an abrasive member secured at an edge to said extension portion. Extension portions may extend from both opposite sides of said U-shaped support member, each having an abrasive member secured thereto allowing bidirectional use of the abrading head and thereby extending the lifetime of the abrading element. It may alternatively be arranged that a single abrasive member in the form of an abrasive sheet is provided. The abrading sheet or sheets are preferably secured with an adhesive to the extension portion or portions. The resilient elements may comprise a plurality of fibres arranged in the manner of a brush, or may comprise a blade-like body as described above.

The invention also resides in an abrading machine comprising a pair of counter- rotating cylindrical drums having a series of generally axially-extending grooves or slots in the outer periphery thereof ( which expression encompasses structures where the slots exhibit a degree of helical curving about the cylindrical drum), each having an abrading element therein as defined above. The invention further resides in an abrading machine comprising a disc-like abrading head having a generally planar or conical abrading face in which there are arranged a series of radially-extending slots or grooves , each having an abrading element therein as defined above. Brief description of the drawings

Embodiments of the invention are now described, by way of example only, with reference to the following drawings in which:

Figures 1 (a) and 1 (b) are schematic cross-sectional views of abrading element constructions according to a first embodiment of the invention;

Figure 2 is a schematic side view of the constructions of Figures 1 (a) and 1 (b);

Figures 3(a) and 3(b) are cross-sectional views of an abrading element construction according to a further embodiment of the invention, in an

undeformed and deformed state respectively; Figure 4 shows part of a drum-like machine head to which is fitted the abrading element construction of Figures 3(a) and (b);

Figure 5 is a variant of the Figure 3 construction employing a foam pad; Figures 6(a) and (b) are a cross-sectional views of abrading element

constructions according to a further embodiment of the invention;

Figure 7 is a side view of the abrading element construction of Figure 6(b); Figure 8 shows in section a particularly preferred abrading element according to a further embodiment, in which an abrasive material is secured by stitches;

Figure 9 show the abrading element of Figure 8 in perspective; Figure 10 shows the abrading element of Figure 8 from the front of the abrasive- carrying surface. Figure 1 1 is a cross-sectional view of an alternative abrading element

construction according to a still further embodiment of the invention employing a thin sheet construction;

Figure 12 shows the abrading element of Figure 1 1 fitted in a machine head;

Figure 13 shows a variation of the Figure 1 1 formed as a multi-element pre-bent construction;

Figure 14 shows an alternative multi-element abrading element form;

Figures 15 (a) and (b) show variants of a further alternative form of abrading element according to a still further embodiment of the invention; and

Figures 16 (a) and (b) show variants of a still further alternative form of abrading element according to a still further embodiment of the invention.

Detailed description of the preferred embodiments

Turning to the figures, Figures 1 (a) and (b) show schematic cross-sectional views of two versions of composite abrasive elements according to a first embodiment of the invention. The abrasive element which is generally indicated 2 has a composite structure comprising a support member 3 and an abrasive material carried on the support member 3. The support member 3 has a mounting portion 4 in the form of a main profile body which is shaped and dimensioned to fit within an elongate recess or slot, preferably an undercut slot, formed within an abrading machine head, making an endwise sliding fit into the slot or recess, and whereby the element can be removed from the head when worn, and replaced by a fresh abrasive element. This main profile body is preferably of dovetail section, but a variety of other shapes adapted to conform to the precise shape of the undercut recess are possible. Moreover, although the main profile body is shown as being of solid form it may be arranged that this is of hollow form, as shown with respect to the embodiment of Figure 3(a) which has the advantage of reducing the material requirement. Extending from this mounting portion 4 is a support portion 6 formed of a strip or blade of resilient material. This support portion 6 may be provided with a series of spaced slits 8 best seen in Figure 2 whereby the individual resilient elements 10 are defined, such that the resilient support portion can readily conform to the shape of the workpiece. The support portion 6 is preferably formed of a resilient plastics material such as an elastomer selected to provide significant resilience to allow the support portion to deform to the shape of the workpiece. More particularly, with appropriate selection of material, height and width of the individual resilient elements 10 as defined between the slits 8, it is possible to accord the support portion with appropriate resilience for the task in hand, and providing the sole means of support for abrasive material, in contrast to conventional structures employing resilient brushes or the like. It is highly advantageous for ease and cost of manufacture if the support 3 can be formed monolithically, for example by an extrusion process, and then subsequently formed with the slits 8, for example by mechanical cutting, thermal cutting or by a laser cutting technique. A variety of polmeric materials may be used, but a particularly preferred material is a vinyl polymer such as EVA (ethylene-vinyl acetate). Further, it may be possible to form the support as a co-extrusion of mounting portion 3 and support portion 6, thereby allowing the option of using different materials for the two portions to further control desired resilience. For example it may be desirable to form the support portion 6 of a material which is less hard than the mounting portion 4, so that the mounting portion 4 is able to be very firmly held in the slots of the head, whilst the support portion 6 is afforded excellent flexibility. It may also be possible to dispense with the slits 8 if the material resilience is sufficient to allow the resilient body to deform sufficiently to conform to the surface of the workpiece, or if a lower degree of deformation is needed, for example if the workpiece is generally planar. Alternatively, the mounting portion and supporting portion may be formed of separate parts joined together.

An abrasive medium 12 is provided in the form of an elongate sheet or web of abrasive material which is secured at its lower long side to a base region of the support portion 6 adjacent the mounting portion 4 and being secured thereto by adhesive indicated 14. The abrasive medium 12 is arranged with the particles provided on that face opposite to the support portion 6. Figure 1 (a) shows a structure with a pair of abrasive media secured to opposite faces of the support portion 6 with their abrasive surfaces facing outwardly, whereby the abrading element 2 can be used in a machine where the head can rotate in a forward or reverse sense. However, for unidirectional use only a single sheet of abrasive medium 12 may be used. The abrasive medium 12 is preferably a coated-type abrasive comprising a flexible backing having abrasive particles thereon, such as a conventional grit-bearing paper or cloth such as sandpaper or the like, although a variety of other known abrasive materials may equally be used depending on the desired abrasive effect. It is also possible to use an abrasive material of a type employing mesh-like construction onto which abrasive particles are bonded. The abrasive medium 12 is likewise formed with a series of spaced cuts 15, whereby individual abrading strips or lamellae 16 are formed, these preferably being aligned with the slits 8 in the support portion 6. In use, as the abrading machine head to which the composite abrasive element 2 is fitted moves over the workpiece, the individual abrading strips deform being supported and urged against the workpiece by the resilient elements 10. The adhesive 14 may take a variety of forms conveniently being a hot-melt adhesive or an adhesive tape. A variety of other fastening means may be used as alternatives to or in addition to adhesive, such as pins or staples or the like, or a stitching technique, depending on the nature of the abrasive medium Figure 1 (b) illustrates a variant of the construction of Figure 1 (a) where the same construction of mounting portion 4 and support portion 6 is utilised, but where an alternative arrangement of abrading material is provided in that this takes the form of individual short abrading strips 18 secured to respective individual resilient elements 10 at or near distal ends of the individual resilient elements 10, by means of adhesive 14 or other fastening means.

Note that Figure 2 is schematic in that the right-hand side of the figure illustrates the construction of Figure 1 (a) with regard to the abrading medium 12, whereas the left-hand side shows the individual abrading strips 18 of the Figure 1 (b) version.

A second embodiment of an abrading element is illustrated in Figures 3(a) and (b) and Figure 4, being generally indicated 20. There is provided a mounting portion 22 of open dovetail section which in use is received within an undercut recess or channel 23 formed within an abrading machine head 25 as shown in Figure 4. Figure 4 shows a machine head of cylindrical drum type where the recess or channel 23 extends along the drum periphery parallel to the drum axis, with the figure showing only a section of the drum. Extending from this mounting portion 22 is resilient support portion 24. Depending on desired resilience, this may likewise provided with a series of slits defining individual resilient elements. In contrast to the earlier-described embodiment the mounting portion 22 is of open hollow form. This results in a reduced material requirement as well as

contributing to its flexibility. The support portion 24 narrows in section towards its distal end remote from the mounting portion 22. As discussed in relation to Figure 1 (a) and (b) the support member comprising the mounting portion 22 and supporting portion 24 may advantageously be monolithically formed, or may be formed by a co-extrusion of the same or different materials, or may be formed of separate parts of different materials joined together. The abrasive medium is secured to the resilient portion 24, with a series of individual abrasive strips 26 being secured to respective individual resilient elements at a location partway up the height of each individual resilient element, being secured by means of an adhesive 28 or other appropriate securing means, such as stitching or staples or the like, or a combination of techniques. As can be seen, the abrasive strips 26 extend beyond the distal end of the supporting portion 24 so that in use the distal ends of the individual resilient elements do not directly contact the workpiece. Figure 3(b) shows the abrading element 20 as undergoing deformation during use as it is pressed against a workpiece.

In the embodiment illustrated in Figure 5 where like parts are indicated by like reference numerals the mounting portion 22 is likewise of hollow form. Here, an additional backing pad 29 of resilient material such as a foam-like material is provided between each abrasive strip 26 and its respective individual resilient element, providing a cushioning function and serving to increase the area of contact of the abrasive strip 26, and which serves to spread the distribution of force and to reduce the risk of excessive abrading force being applied to a workpiece. The abrasive strip 26 is secured to this backing pad 29 by means of an adhesive or other securing technique, which backing pad 29 is in turn secured to the individual resilient element by an adhesive or other securing technique. It will be noted that the abrasive strip 26 extends beyond the end of the backing pad 29, such that the backing pad 29 will not directly contact the workpiece. Turning to Figure 6(a) there is illustrated an embodiment of an abrading element generally indicated 30 in which, in similar manner to the embodiment of Figure 1 , there is a support member having a dovetail-sectioned mounting portion 4 from which extends a resilient supporting portion 32. Depending on desired resilience, this supporting portion 32 may likewise be provided with a series of slits whereby a series of individual resilient elements 33 are defined. In contrast to the Figure 1 structure each individual resilient element is formed at its distal end remote from the mounting portion 4 with an enlarged edge region 34. This has a slightly tapering upwardly-narrowing profile. This enlarged edge region 34 carries abrasive material, for example in the form of an abrasive strip 36 secured thereto, such as a strip of sandpaper or the like, or an abrasive pad containing a matrix in which is embedded abrasive particles. Alternatively or additionally, the abrasive material may comprise individual abrasive particles or agglomerations of particles 38 secured to and/or embedded in the enlarged edge 34. These abrasive particles 38 may be secured to the enlarged edge 34 by means of an adhesive or they may be embedded in an additional matrix material layer applied to the enlarged edge 34. Alternatively, it may be arranged that the abrasive particles 38 are embedded in the enlarged edge 34 at its time of formation, for example, being introduced into the material of the enlarged edge as it is moulded or extruded. In a particularly advantageous form the mounting portion 4, and resilient body 32 and enlarged edge 34 are monolithically formed, for example by moulding or extrusion, or as a co-extrusion.

In the embodiment of Figure 6(b) and Figure 7 a generally similar structure is shown where like parts are indicated by like reference numerals. A mounting portion 4 of dovetail section is provided from which extends resilient support portion 32. Here a body of abrasive material 40 is secured to the upper distal end of each of the individual resilient elements 33. As illustrated this preferably has an upwardly tapering profile, whereby the angle through which the individual resilient elements 33 must deform in order that a surface of the abrasive material body 40 is generally flat against a workpiece is reduced as compared to an abrasive material body having surfaces parallel to the extent of the support portion 32.

Figures 8, 9 and 10 show a particularly preferred embodiment. The abrading element 41 illustrated therein has a support 42 to which is secured a strip of abrasive material 43. The support 42 comprises a mounting portion 44

comprising a hollow profile of dovetail section for receipt in the undercut recess 45 in the machine head, and extending from the mounting portion 44 a support portion 46. Figure 9 shows the abrading element in a perspective view in which the slits 47 in support portion 46 and abrasive material 43 are visible. The support is formed of a resilient material such an elastomer or near elastomer such as EVA (ethylene-vinyl acetate ) or PVC (polyvinyl chloride) . The support portion 46 is of upwardly tapering profile away from the mounting portion 44, with the profile, material selection and slits arranged whereby the support portion is able to exhibit a significant deformation as the abrading element is urged against a workpiece, whilst still providing a significant degree of support and return force for the abrasive material against the workpiece, and returning to the non- deformed position when no longer in contact with the workpiece. The dotted lines in Figure 7 indicate deformation of the support portion 46 as urged against a workpiece. The abrasive material may take a variety of forms as discussed above, but preferably is an abrasive grit-based paper or the like. This is secured to the support portion 46 by a combination of an adhesive and by sewing using stitches of a yarn or thread or a synthetic line or the like, with the row of stitches indicated 48. The stitches are provided a approximately a quarter of the way up the abrasive material from the edge adjacent the mounting portion 44. This combination of adhesive and the sewing technique is found to provide a particularly effective securing of the abrasive material, which is necessarily subjected to significant forces during use. A single line of stitching 48 is illustrated and is found to be sufficient, but additional stitching may be provided if desired. The abrading element 41 may have a variety of dimensions according to the task in hand but an advantageous dimension for fitting to a head with slots of depth of 7mm and slot base width of 8mm has a support of height of about 50mm, support portion tapering from 1.75mm thickness at the base to about 0.75mm at the tip, a height of abrasive material of about 45mm, a height of slots of about 27mm, and lateral separation of slots of about 25mm.

A further alternative embodiment of abrading element is illustrated in Figures 1 1 and 12. In contrast the previous-described embodiments the abrading element of this embodiment is formed of a thin sheet of material which is bent or otherwise formed into the desired shape, such as a thin sheet of a springy metal. A variety of metals may be used but steel is preferred for convenience and cost. As an alternative to a metal a plastics material might be utilised, for example formed by extrusion, or a composite material may be employed. More particularly, the abrading element which is indicated generally 50 comprises a support which has a mounting portion 52 at which it is formed to define a profile which in use is fitted into the undercut recess 23 of the machine head, which profile portion is preferably an upwardly-narrowing U-shaped channel shaped to correspond to the shape of the recess, and dimensioned whereby the profile portion must be slightly deformed to fit therein and make a tight fit. Extending from the mounting portion 52 is a support portion 54 which forms the main face on which abrasive material is disposed. As can be seen in Figure 9 this may be formed with slits 56 which extend from the distal edge almost to the mounting portion 52 defining a series of individual resilient elements 58. This support portion can take a variety of forms, being generally planar, or as is shown can advantageously be curved towards the distal edge, curved slightly back towards the drum surface, defining an outwardly protruding nose 60, this being the portion which contacts the workpiece. The support portion 54 is provided with abrasive material indicated 62 at this distal edge and in particular at this protruding nose region 60. The abrasive material may comprise an abrasive coating containing abrasive particles, or an abrasive material secured to the surface of the support portion 54 such as a sandpaper or the like. In a particularly effective implementation in terms of its effectiveness and durability the abrasive medium is a diamond coating applied by an electroplating technique. At the opposite side to the abrading face the mounting portion 52 extends to form a bent over short lip 64 which assists in locating and holding the mounting portion 52 within the recess 23 assisting to prevent its movement within the recess, this bent-over region engaging the edge of the recess. In an alternative version illustrated in Figure 13 which has particular applicability to use on a drum-type machine head, instead of providing a plurality of individual abrading elements 50 fitted within respective recesses, a multiple-element structure 70 may be provided where a series of interconnected abrading elements are provided. Here the multi-element structure 70 likewise includes mounting portions 52 at which the structure is held on the machine head in respective recesses, but the support portions extend as outwardly curving portions 72 each interconnecting between a pair of mounting portions 52, with the abrasive material indicated 74 provided at least on the outward nose-forming extremity of these interconnecting curving portions 72. This mutli-element structure may comprise a complete sleeve-like structure which completely surrounds a machine head drum with adjacent mounting portions 52 fitting into adjacent recesses, or alternatively may comprise a smaller structure associated with a smaller number of the machine head recesses and where a number of these multi-element structures are employed on the machine head. In this case, at an edge of a particular multi-element structure the free edge will have the structure of the embodiment of Figure 1 1.

It may be arranged that the multi-element structure 70 is pre-formed into essentially the final shape as shown in Figure 13 before it is fitted onto the drum. Alternatively, the structure may prior to fitting have the generally planar shape as shown in Figure 14, requiring that the structure be deformed on fitting so that in the abrading regions the material is in compression, or alternatively a shape between these extremes may be used i.e. more limited pre-forming deformation may be used so that a limited bending is needed on fitting to the drum.

Figures 15(a) and (b) show schematic cross-sectional views of two variants of abrading elements according to a still further embodiment of the invention. The abrading element which is generally indicated 80 comprises a main profile body 82 for fitting to the abrading machine head of an abrading machine. This main profile body 82 is preferably of dovetail section, but a variety of other shapes adapted to conform to the precise shape of the undercut recess are possible. To this main profile body 82 there are secured resilient elements in the form of a plurality of resilient filaments or bristles 84 forming a brush-like arrangement. These filaments 84 may be secured to the main profile body 82 by a variety of means such as being fitted into openings in the profile body and secured therein by adhesive or welding or staples or pins or the like or other conventional fasteners. Conveniently, the filaments are arranged in bundles where each is folded at its middle and secured within an opening in the main profile body at the fold by a staple. There is provided an additional profile part 86 which forms a support portion, this being of generally U-shaped section having opposed walls 88 which follow the upward narrowing of the main profile body 4 and which enclose the main profile body 82. The main profile body 82 and additional profile part 86 serve to retain the abrading element 80 on the machine head, fitting within an elongate undercut recess or slot formed within the abrading machine head, making an endwise sliding fit into this slot or recess. In particular, as the head rotates the profile body 82 and additional profile part 86 are forced tightly against the edge of the slot. From the opposed walls 88 of the additional profile part there extend parallel upwardly-extending portions 90. In use, when fitted within an undercut slot or recess within the machine abrading head the extending portions 90 extend outwardly beyond the slot or recess. An abrasive medium such as a sheet of abrasive material 92 is secured by means of adhesive 94, stitching, staples or other means to these extending portions 90. Figure 12 (b) illustrates a version with a single abrasive sheet 92 secured to one of the extending portions, whereas Figure 12(a) shows a version where a pair of abrading media 92 are provided on respective extending portions 90. This construction of Figure 15(a) allows the machine head to produce an abrading effect if operated in either of a forward or reverse direction, and which thereby extends the useful life of the abrading element in that once one strip abrasive material is too worn to be used the machine can be operated in the opposite direction to use the other strip of abrasive material. The structure of the U-shaped profile can equally be utilised in connection with a resilient element having the form of the support portion of the previously- described embodiments where this is a blade-like member. Figures 16(a) and (b) show a structure where the U-shaped profile of Figures 15(a) and (b) is used in connection with the support portion of Figures 3 to 5, and where like parts are referenced by like numerals. Thus, the abrading element generally indicated 100 has a main profile body portion 22 from which extends resilient body portion 24 of outwardly narrowing form. This is held within additional U-shaped profile part 86 which in use engages within a slot or undercut recess within the abrading head. Although illustrated schematically for ease of understanding with some clearance between the opposed walls 88 of the profile part 86 and the main profile body portion 22, in practice these will preferably make a tight fit. As illustrated in Figure 16(a), this additional profile part 86 has a pair of upwardly extending portions 90 which protrude out of the machine head slot or recess, to which are secured respective abrasive sheets 92 through adhesive 94 or other fastening means. The variant in Figure 16(b) has only a single extending portion 90 and abrasive sheet 92, for unidirectional use. Although the main body profile portion 22 and resilient support portion 24of the embodiment of Figures 3 to 5 are shown, equally, the construction of mounting portion and support portion of Figures 1 and 2 might be utilised in connection with the U-shaped profile part 86.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made without departing from the scope of the invention.