Abstract:
A sanding apparatus includes a plurality of sheet elements with exposed, abrasive edges. These sheet elements are biased outwardly with respect to the housing by a compressible foam block. The exposed abrasive edges together define a conformable abrasive surface for sanding moldings and the like. The plurality of sheet elements may include a replaceable cassette.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to sanding apparatus for sanding flat surfaces and profiles such as architraves. 
     The fine detail and curvatures of such profiles make them awkward to sand, either manually or by machine. Where cost has not been an important factor it has been known to make a complementary or negative profile and then to use this as a sanding block to push a sheet of sand-paper into contact with the profile to be sanded. However this is not practical or economically realistic in most cases. Alternatively, the sand-paper may be folded to allow it to reach the bottom of the grooves in the profile, but this is time consuming and not particularly effective 
     There is therefore a need for a sanding apparatus which facilitates sanding of a profile, for example prior to painting. 
     DESCRIPTION OF THE RELATED ART 
     British Published Patent Application 2 256 383A discloses an arrangement in which a number of sheets are mounted in a block. The sheets are moveable during an adjustment phase to allow them to shift relative to each other to conform to a required profile, whereafter the sheets are locked in this position by a clamp. There is also mention of a system in which the sheets are replaced by a deformable material and also an arrangement in which the sheets are made of a rubber type material. There is however no mention of an arrangement in which a number of parallel sheet elements are mounted side by side for relative movement against a resilient bias. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspects this invention provides a sanding apparatus for sanding a profile such as an architrave, which apparatus comprises a main body portion, a plurality of parallel sheet elements mounted side by side in said body portion for relative movement to each other and said body portion against a resilient bias, with respective exposed edges of said sheet elements together defining a conformable abrasive surface. 
     The exposed edges of said sheet elements each define abrasive edge surfaces. Thus the sheets may carry an abrasive coating on the exposed edges or they may be made of a suitable matrix material such as a plastics or other tough but abradable material, incorporating abrasive particles. 
     The exposed edges are preferably rounded in cross-section instead of having sharp 90° edges, to reduce the possibility of producing a striped effect. 
     The lengths of the exposed edges of the sheet elements are preferably selected such that together they define a wedge shaped leading region to the abrasive surface when it is viewed in plan. 
     Preferably, said sheet elements are slidably received in an aperture in said main body portion. Said bias means may take many forms. In one particular arrangement, the bias means may comprise an element of resiliently compressible material such as a foam or sponge synthetic material in block or any other suitable form. Alternatively, the bias means may comprise a first elastically deformable component, for example of a foam or sponge material, and a load-spreading or equalising component such as a fluid or gel-filled sac, which acts to distribute the contact pressure substantially evenly between the sheet elements. In another arrangement, the load-spreading or equalising component may comprise a number of loose packed rods or rod-like elements capable of shifting with respect to each other to substantially equalise the pressure applied to the sheet elements. 
     The sanding apparatus may be designed for manual use or adapted for use with a power tool. In this latter embodiment, the apparatus and/or tool preferably includes means for oscillating said apparatus in a direction generally parallel to the direction of said sheet elements. For example, a power tool may include an outer guide element within which the main body portion is constrained to slide back and forth but not side to side. The body portion may be driven back and forth by a reciprocating mechanism similar to that used in a powered jigsaw, although many other mechanisms could be used. 
     In one embodiment of a power tool of this sort, the alternate sheets may be reciprocally driven in common, in antiphase to the intermediate sheets, to provide a dynamically balanced arrangement which ensures that a major portion of the vibratory effect is applied to the abrasive surface/workpiece interface with minimal vibrational energy being transmitted to the hand or structure supporting the tool. 
     Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be formed in various ways, and, by way of example only, an embodiment thereof will now be described in detail, reference being made to the accompanying drawings, in which: 
     FIG. 1 is a schematic general perspective view of a sanding apparatus of this invention; 
     FIG. 2 is an underplan view of the conformable abrasive surface of the sanding apparatus of FIG. 1; 
     FIG. 3 shows the apparatus of FIG. 1 when applied to a typical moulded profile; 
     FIG. 4 shows an alternative form of sheet element for use in the sanding apparatus; 
     FIG. 5 is a schematic section view of another embodiment of sanding apparatus of this invention; 
     FIG. 6 is a schematic section view of a further embodiment of sanding apparatus of this invention; 
     FIG. 7 is an exploded, part-sectioned perspective view of a further embodiment of sanding apparatus of this invent ion; 
     FIG. 8 is a perspective view of the further embodiment of FIG. 7, part-assembled; 
     FIG. 9 is a schematic view of a powered embodiment of sanding apparatus in accordance with this invention, and 
     FIGS.  10 ( a ) ( b ) and ( c ) illustrate an alternative lapping or staggered arrangement and sheet elements for use in embodiments of the sanding apparatus of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the sanding apparatus comprises a main body portion  10  defining an internal chamber which is filled with a block of compressible foam or rubber material and has two depending side plates  14 . Between the side plates  14  slidably mounted a stack of relatively slidable sheet elements  16 . The sheet elements  16  are retained, and their extent of movement controlled, by means of two pins  18  which extend between the side plates  14  through respective slots  20  in the sheet elements  16 . The lower edges of the sheet elements are rounded and either coated with or incorporate an abrasive material. 
     The lengths of the sheet elements are profiled, as seen in FIG. 2, so that the abrasive surface defined by the edges of the sheet elements  16  has a wedge shaped leading edge region. This is to facilitate sanding of a mitred frame  22  up to the mitre joint line  24  (shown in dotted lines). 
     In use, the apparatus is applied to a profile and, as seen in FIG. 3, the sheet elements retract against the bias of the spring or foam block  12  to conform closely to the profile. The profile may then be sanded by moving it back and forth. The sheet elements preferably can flex slightly to accommodate slight misalignment. 
     Referring to FIG. 4, an alternative form of sheet element  16  is formed with integral spring retention tags  26  which obviate the need for the pins  18  and slots  20 . In use the tags  26  hook behind a ledge or abutment inside the body portion  10  to retain the sheet element. 
     Referring now to FIGS. 5 and 6, as previously the sanding apparatus comprises a housing  30  with a number of parallel sheet elements  32  with exposed abrasive edges and located for limited relative sliding movement by means of two pins (only one of which is shown) locating in aligned slots of the sheet elements  32  to allow relative sliding movement. In the upper part of the housing  30  is provided a resilient foam block  36  which is elastically deformable. In a lower part of the housing, and contacting the upper edges of the sheet elements, is a load-spreading component. In FIG. 5 the component is in the form of a fluid or gel filled sac  38 , for example filled with a silicone plastics material. In FIG. 6, the load-spreading component comprises a number of loose packed rods  40  which can roll and slide with respect to each other. 
     In both FIGS. 5 and 6, the foam block provides a resilient force whereas the gel sac  38  or the rods  40  spread the load across the tops of the sheet elements so that the contact pressure between the exposed abrasive edge of the sheet element and the workpiece is generally constant. 
     In use, as with the earlier embodiment, the sheet elements are free to slide with respect to each other and thus to adjust to follow changes in profile. 
     Referring now to FIGS. 7 and 8, the third embodiment of the invention is of broadly similar construction to the previous embodiments. Here the tool  50  is formed of a two part casing comprising a top moulding  52  and a lower moulding  54 . The lower moulding is provided with generally vertical walls defining a generally rectangular aperture  56 , which receives the stems  58  of a stack of generally T-shaped sheet elements  60 . The stack of sheet elements  60  are releasably and slidably located with respect to the lower moulding by means of a pair of pins  62  which pass through aligned pairs of parallel slots  64  in the sheet elements. The pins have enlarged heads  66  larger in diameter than the width of the slots which retain them in the slots to provide a replaceable “cassette”  68  comprising the sheet elements and the pins, which can be replaced when required, for example where a finer or coarser grit is required, or where the sheet elements need to be replaced The cassette  68  is located within the recess by removing the top moulding  52  and offering the cassette up to the rectangular aperture  56  from below and passing the pin heads  66  along respective J-shaped channels  70  formed in the sides of the aperture  56  to be retained by a cupped ledge  72 . The top moulding  52  is then re-attached, and a retention rim  74  prevents inadvertent dislodging of the pins from the ledger  72 . 
     The top moulding  52  comprises an outer pattern which merges with the lower moulding  54 , and an inner downwardly open rectangular housing  76  which provides the retention rim  74 , within the housing is contained a foam or other resiliently compressible block which in use is located against the top of the sheet elements  60  to bias them downwardly. 
     Referring now to FIG. 9, this shows schematically a powered version of the sanding tool. As previously, the sheet elements  80  are slidably mounted in a housing  82  and resiliently biassed towards the workpiece and these features will not be described in detail again. But here the sheet elements are driven reciprocally within the housing. The sheet elements could all be driven in unison but to provide dynamic balancing in this arrangement one set of alternate sheet elements  80  is connected to one drive arm  84  and the intermediate sheet elements  80  are connected to another drive arm  86 . The drive arms are driven in antiphase by a stepped eccentric drive shaft  88  which provides two longitudinally spaced eccentric surfaces  90 ,  92  which are 180° out of phase, and which drive the arms  84  and  86  by means of cam followers  94 . 
     Referring now to FIGS.  10 ( a ), ( b ) and ( c ), in the arrangements of sheet elements described above there are slight gaps between the adjacent rounded portions of the sheet elements, as shown in FIG.  10 ( a ). In many cases this will not matter greatly as there is likely to be some lateral movement of the sheets during sanding, to prevent small ridges forming. If however this is perceived as a problem a lapped arrangement of sheet elements may be provided so that, when seen in end view in FIG.  10 ( b ) there is an intermediate or bridging sheet  96  between the main sheet elements  98 . For this arrangement the main sheet elements  98  include on one side a spaced pair of recesses  100  and on the other a plain channel  102  extending through the depth of the main sheet element. The main sheet elements are positioned so that the plain channel and stepped recesses face each other and sandwich the bridging sheet  96  which has a channel defined by two lands  104  which limit movement of the bridging sheet to prevent it falling out. The main sheet elements and the bridging sheet elements are all biassed downwardly by a resilient foam block or the like.