Regulation 3.2 AUSTRALIA PATENTS ACT, 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL Name of Applicant: RONALD LINDSAY DUNLOP Actual Inventors: DUNLOP, Ronald Lindsay Address for service in A j PARK, Level 11, 60 Marcus Clarke Steet, Canberra ACT Australia: 2601, Australia Invention Title: Formwork Assembly And Formwork Element For Casting Concrete Components The following statement is a full deseaiption of this invention, including the best method of performing it known to us, 33m77_n.oc 2 FIELD OF THE INVENTION The invention relates to a formwork system for pre-casting concrete. In particular the invention relates to a modular and adjustable boxing system to assist in preparing pre-cast concrete components for use in the construction industry. While the invention is particularly 5 described in connection with concrete construction, it may have application to other construction materials and to other settable materials. BACKGROUND TO THE INVENTION The use of precast concrete components such as slabs, columns etc in the construction 10 industry is well known. This avoids the need for casting concrete components in situ and renders unnecessary the extra formwork and labour needed to pour, form and hold wet concrete in place until it sets. The components can instead be precast offsite, or at least away from the main construction area, and when needed the components are transported by truck and/or lifted into position by crane and incorporated into the existing structure. 15 Pre-casting is typically performed in horizontal casting beds with the extremities of the required components defined by formwork typically in the form of L-shaped extrusions. As will be appreciated, the maximum height of the component being formed will be determined by the height of the L-shaped extrusion. Thus, it may be necessary to have lengths of founwork of varying heights to suit a range of casting jobs. This is particularly necessary if components are 20 cast progressively on top of each other. Concrete can be brittle and easily chipped or broken where it is thinnest in a component. Typically this occurs on the corners and edges of the component during renoval from the mould, transportation and placement. Such damage, which may lead to weakness and which looks unattractive where the components are to remain exposed in a structure, can be avoided by 25 providing the component with chamfered edges. An existing method used to create the chamfer involves placing a plastic triangular sectioned component at the bottom corner of the mould created by the L-shaped sections. However, it will be appreciated that this only allows for the edge at the bottom of the mould to be chamfered, LS patent 7,584,540 describes a formwork system including a plurality of elongate casting 30 elements, which can be arranged in a casting substrate and include at least one channel to hold a wall portion. The casting elements are arranged as a perimeter of the component to be cast and the wall portions are located in the channels to limit the sides of the component to be cast. The casting elements are anchored to the substrate. The casting elements may optionally include a chamfering portion to chamfer the edge of the component. The casting element is typically an 35 extruded aluminium product, with four embodiments illustrated in Figures 1, 6 and 7. mn7737 IoL 3 US patent 4,183,497 describes a system including casting elements in the form of a channel. The casting elements are arranged on the substrate and secured through the base channel, and wall portions are subsequently arranged on edge in the channel to form the edge of the concrete component. 'This casting element includes a chamfering portion on either side of the channel. 5 In either of the described systems, a second set of casting elements may be provided along the top edge of the wall portions, to provide a chamfer around both perimeter edges of the panel. US 7,584,540 also describes (with reference to Figure 9) a method of using the casting elements to form concrete columns with chamfered vertical edges. It is an object of the present invention to improve the finish of the concrete component 10 formed using systems as described above. SUMMARY OF THE INVENTION In one aspect, the present invention may broadly be said to consist in a system for casting concrete components comprising a plurality of casting elements, each casting element including a 15 channel for receiving an edge of a wall portion, a plurality of wall portions, each wall portion having a length, a width and a thickness, the length being greater than the width and the width being greater than the thickness, the width and length of the wall portion together defining each of two faces of the wall portion, and the length and thickness of the wall portion together defining two edges of the wall portion, an edge of each wall portion being dimensioned for 20 insertion into the channel of the casting element, and a face of each wall portion being defined by a first planar portion running the length of the wall portion and being spaced along its length from an edge of the wall portion by a stepback, the width of the stepback being less than or approximately equal to the depth of the channel of the casting element, and wherein the depth of the stepback approximates the radius or thickness of the free edge of the channel such that with 25 the wall portion assembled into the casting element, with the casting face of the wall portion facing the intended casting cavity, the casting face surface of the free edge of the channel of the casting element and the planar portion of the wall portion substantially abut without forming a step on the cast face of the concrete component. According to a further aspect, the face of the wall portion includes a stepback along the 30 length of the wall portion adjacent each edge of the face. According to a further aspect, another face of the wall portion includes a second planar wall portion running the length of the wall portion and spaced along its length from an edge of the wall portion by a stepback. According to a further aspect, the other face of the wall portion includes a stepback along 35 the length of the wall portion adjacent each edge of the face. 3377757. LDOC 4 According to a further aspect, the stepback depth is at least 0.5mm and less than 10mm. According to a further aspect, the thickness of the free edge of the channel is between 0.5mn and 5nn, and the stepback depth is between 0.5mm and 5mm. According to a further aspect, the stepback depth is greater than 0.5mm and less than 80% 5 of the thickness of the wall portion. According to a further aspect, the thickness of the wall portion is less the depth of ihe stepback is greater than 6mm. In a further aspect, the thickness of the portion of the wall portion that engages in the channel of the casting element is greater than 6mnIn 10 In another aspect, the present invention may broadly be said to consist in a wall member for use in a system for casting concrete components that includes; the wall mcmbcr comprising a plurality of casting elements, with each casting element including a channel for receiving an edge of a wall member, a member having a length, a width and a thickness, the length being greater 15 than the width and the width being greater than the thickness, the width and length of the member together defining each of two faces of the member, and the length and thickness of the member together defining two edges of the member, an edge of each member being dimensioned for insertion into the channel of the casting element, and a face of each member being defined by a first planar portion running the length of the member and being spaced along its length from 20 an edge of the member by a stepback, the width of the stepback being less than or approximately equal to the depth of the channel of the casting element, and wherein the depth of the stepback approximates the radius or thickness of the free edge of the channel such that with the member assembled to the castimg clcmcnt, with the casting face of the member facing the intended casting cavity, the outer surface of the free edge of the channel of the casting element and the 25 planar portion of the member substantially abut without forming a step between. According to a further aspect, the face of the member includes a stepback along the length of the member adjacent each edge of the face. According to a further aspect, another face of the member includes a second planar surface running the length of the member and spaced along its length from an edge of the member by a 30 stepback. According to a further aspect, the other face of the wall portion includes a stepback along the length of the wall portion adjacent each edge of the face. According to a further aspect, the stepback depth is at least 0.5mm and less than 10mm. According to a further aspect, the stepback depth is greater than 0.5mm and less than 50% 35 of the thickness of the wall portion. 33 77757.DOC 5 According to a further aspect, the thickness of the wall portion less the depth of the stepback is greater than 6mm. According to a further aspect, the thickness of the portion of the wall portion that engages 5 in the channel of the casting element is greater than 6mm. By depth of stepback we mean the offset between the face of the wall portion that forms a mould surface and the face that is inserted in the channel of the formwork element. The overall thickness of the wall portion is measured at a location outside the fornwork element, for example, at a concrete contacting surface of die board (in a single contacting face version), 10 To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims, The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. The term "comprising" is used in the specification and claims, means "consisting at least in 15 part of'. When interpreting a statement in this specification and claims that includes "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 shows perspective views of two embodiments of a casting element of the prior 20 art. Figure 2 is a perspective view of an assembled apparatus of the prior art. Figure 3 is a cross-sectional view showing the apparatus of Figure 2 in use. Figure 4 is a cross section view of casting elements of the prior art assembled with a board of the prior art, and illustrating the finished edges of cast concrete components. 25 Figure 5 is a cross section view of casting elements of the prior art assembled with a board of the prior art, and illustrating the finished edges of cast concrete components. Figure 6 is a perspective view of an alternative prior art embodiment of a casting element. Figure 7 is a perspective view of yet another prior art embodiment of a casting element. Figure 8 is a cross-sectional view of another prior art embodiment of a casting element. 30 Figure 9 is a cross -sectional view of a further prior art embodiment of an assembled apparatus. Figure 10 is a cross section of a casting element and assembled board incorporating aspects of the present invention and finished edges of concrete components thus formed. m337 oc57 I ivy 6 Figure 11 is a cross section of a casting element and assembled board incorporating aspects of the present invention and finished edges of concrete components thus formed. DETAILED DESCRIPTION OF THE INVENTION 5 The present invention relates to a casting system including casting elements such as those described in US patents 4,183,497 and US 7,584,540, and improved boards or wall portions to provide a better finished edge to the concrete components. The arrangement and operation and use of the casting elements will first be described with reference to Figures 1 to 3 and 6 to 9. The limitations of these systems, addressed by the present invention will then be described with 10 reference to Figures 4 and 5 and the improvements according to the present invention will then be described with reference to Figures 10 and 11. Referring to Figure 1, the casting clement is of elongate form with a constant cross-section. The element is designed to rest on its base 1 on a solid surface known in the art as a casting bed 2, as shown in Figure 2. 15 Channels 3 are provided on both sides of the element to accept substantially rectangular planar sheets 4 that define the sides of the component to be precast. The transverse width (height) of a sheet depends on the size of the side of the component to be precast. The thickness of the sheet is uniform and typically less than 18 mm so as to fit in the channeL The longitudinal length of the sheet is typically of a standard length shorter than the clement. 20 A shaping surface 5 of the element may fill in the apex of the angle defined by the base and the outer side of a channel 3 so as to form a chamfered edge on the component, as shown in Figure 2. Two embodiments of the element with flat and concave shaping surfaces are depicted in Figure 1. Preferably the projection SA forning the shaping surface is substantially a right angled triangle in cross-section as shown. 25 A raised central I-section 6 has two sides, a bridge 6A and inwardly directed flanges 7 that define a cavity 8 and a slot 9 that both run the length of the element. The sides of the H section define respective inner walls of the channels 3 and the projections 5A define respective outer walls of the channels. A plurality of holes 10 are formed in the bridge of the central H-section, spaced out along the length of the element. 30 Two elements and two sheets are assembled into the apparatus shown in Figure 2. This apparatus serves to form a vertical side of two components to be cast side-by-side. The number of elements and sheets required in use to cast a coniponent will depend on the size and shape of the component. It can be seen that the apparatus comprises a first lower element AA resting on a castig bed with the required sheets inserted into the channels on the first element. A second .1m377 neoc 7 element BBis then inverted and placed on top of the sheets so that the upper ends of the sheets fit into the channels of the second element. Preferably the apparatus is held together using a bolt 11 that passes through the hole 10 and slot 9 in the upper element BB, and through the slot in the lower element to terminate in the 5 cavity 8 of the lower element AA. Nuts 12A and 12B having internal threads corresponding to external threads on each longitudinal end of the bolt, engage the elements and, when tightened on the bolt, draw the elements together to bear upon the sheets, locking the apparatus together. As shown in Figure 2 the nut 12A on the upper end of the bolt rests in the U-shaped channel on the underside of the element BB defined underneath the raised section 6. The nut 12B on the 10 lower end of the bolt is positioned in the cavity 9 and held against the underside of the flanges 7 by an optional spring 12C. The nut 12B bears upon the underside of the flanges when it is threaded onto the bolt, Preferably neither the nut nor the bolt project above the base of the upper element BB to allow for screeding by methods known in the art. The bolts 11 may be equally spaced along the length of an element. 15 Figure 3 shows an embodiment of the apparatus in use. Bolts 13 (offset from bolts 11) are passed through holes 10 in the lower element .AA to anchor the element in place on the casting bed. It can be seen that the shaping surfaces 5 provide a chamfer on the edges of the component 14. If necessary, reinforcing material 15 can be included in the precast clernent according to methods known in the art. In particular, reinforcing may be included by forming holes in the 20 sheet 4 of a mould and passing such reinforcing as required through to project into the nould. Optionally the reinforcing may project through corresponding holes in the sheets on opposite sides of the mould to pass through the entire width or length of the mould. Such reinforcing may be placed under tension to form pre-stressed concrete as known in the art. Inserts (not shown), suh as nuts, may be included in a component by attachment to the mner face of a sheet 25 4 using plastic nail plates or other methods as known in the art. It will be appreciated that functionally equivalent methods of anchoring the elements to the casting bed and attaching the elements to each other are possible. For example, the nut 12B could be tack-welded in place or alternatively could be replaced by a washer and bolt arrangement, or a bolt 11 with a suitably sired head. 30 in a typical set of elements and sheets for pre- casting concrete components, preferably the elements are of a uniform length longer than die longest sheet. This aims to ensure that joins between sheets do not correspond to joins between elements, except where a corner is required as explained above and shown in Figure 4. The sheets 4 may be practically any size or shape. 33 7 77 1 .DOC B In a preferred embodiment the element is extruded from aluminium or plastic. Alternativelv, the elements may be formed using glass fibres and reinforced with resin (fibreglass). Alternatively, the casting element may be folded or rolled from sheet metal. The sheets are preferably made of plywood. Other suitable materials include timber, steel, and 5 plastics. Figure 6 illustrates an alternative form of a casting element. Compared to the embodiment illust.tated in Figure 1, the bridge 6a is lowered to align with the base to thereby form a level base 22 as shown. This defines a channel 24 running the length of the element. Furthermore, instead of the projections 5a being formed with three sides, only two sides of the projection are formed 10 including a first part as an extension of the base and a second part which is a shaping surface which defines the chamfer on the element to be cast. Nevertheless, the projections still define two channels 20 running the length of the casting element to receive the sheets 4 to define the walls. Figure 7 illustrates yet another embodiment of the casting element 50. It will be seen that 15 this embodiment of the casting element 50 does not include the projections to form the chamfers. Instead, the outer edges of the casting element 50 have two plane upturned walls 21 to define two U-shaped channels to receive the edges of the sheets 4. It will be appreciated that the casting elements of the invention may define a curve along their longitudinal length, 20 Figure 8 illustrates a cross-section of a casting element designed to be curved along its length. The particular form of the casting element includes a bridge 30 with the base being continuous across the bottom of the element as shown to define a cavity 32. Additionally, one of the chamfering portions 34 may be removed as illustrated by the part in phantom. The section may be rolled around the Y-Y axis to a desired radius. The centre of the radius may originate 25 from either side of the element. The section may be rolled into a curve, a circle or into a serpentine shape. Alternatively, the section may be rolled around the X-X axis with the centre of the radius originating from either above or below the section. This may have particular application when casting vertically oriented components as will be explained further in connection with Figure 9. 30 Figure 9 illustrates an alternative apparatus used to form vertical column in sitr. Whilst the figure illustrates a manner of forming a column, the same approach can also be applied to forming a wall or any other kind of vertically oriented component. Two casting elements 42 are anchored to a substrate 46 in spaced disposition. The substrate 46 may be a form as used in convention form work. The two casting elements 42 and 35 the substrate 46 may then be vertically oriented. Similarly, two further casting elements 42 may 3377757 1.LD C 9 be affixed to a second substrate 46 and oriented to face the first mentioned assembly. The two remaining sides of the column can then be defined by two sheets 48 each received in the innermost U-shaped channels of opposed casting elements. The entire assembly is mounted on a base defined by a series of casting elements 50 (of 5 Figure 7. These casting elements 50 may be secured to the construction site with each of the sheets 48 inserted into one of the U-shaped channels of one of the casting elements 50. Furthermore, the upright forms 46 may be likewise received in channels of one of the casting elements 50. When the assetnbly is in place, the column fornwork can be strengthened using the threaded bolt 52 to clamp the two forms 46 together. 10 Figures 4 and 5 illustrate limitations of these prior art casting systems. Figure 4 illustrates a casting element 401 that includes a single channel 403 that is used both to secure the casting element 401 to the substrate and to locate the lower edge 405 of the board 407. A second casting element 403 may be secured to an upper edge of the board 407. The casting element 401 (and 4.03) includes, for illustration, a chamfer forming portion 409 along one edge, which in use, will 15 form a chamfer on the cast concrete component. To illustrate an alternative in the same figure, the illustrated casting element 401 includes a plain side 411, forming the other side of the channel 403. The casting element may include instead, a chamfer-forming portion along each side, or a plain wall portion along each side of the channel. The board 407 includes edges 420 and 422. Edge 420 is located in casting element 413. 20 Edge 422 is located in the channel of casting element 401. Each edge is defined by the thicless and length of the board. The board includes a first face 424 and a second face 425. Each face is defined by the width and length of the board. The length of the board is greater than the width of the board and the width of the board is greater than the thickness of the board. The sides of the channel 403 of each casting element butt against the faces 424 and 425. The remainder of the 25 face (beyond the edges of the board that are lodged in the channels) are exposed. In use, at least one of these faces forms part of the casting cavity for the concrete component. In some production arrangements, concrete components can be formed adjacent both sides at the same time. Figure 4 illustrates the particular effect of each arrangement on the cast concrete 30 component. In particular, the cast concrete component 426 includes an edge face 427 with chamfers 429. Between the edge face 427 and each chamfer 429, there is a transition. The transition includes a change in angle between the end face 427 and the chamfer 429, but also includes a small step 430. The small step 430 results from the radiused edge 431 of the casting element. The size of this step 430 could be reduced by reducing the radius of the edge 431, but 35 this would lead to a sharp edge, making it difficult to insert the board cleanly into the channel, 3377Y71Dotic 10 with the sharp edge of the channel likely to bite into surfaces of the board. Practically, a significant radius is required and thus a noticeable step 430 is produced. In the other illustrated arrangement where a plaim edge is required on the concrete component, the concrete component 440 has an edge face 442 which ideally would be planar 5 right to its edges 444. However, in this case, the edge face 442 includes a stepback 448 formed adjacent to each edge 444 by the presence of channel side portions 450. Referring to Figure 5, similar problems arise with the use of the casting element including a central channel for securing the casting element to the substrate and a further channel, or channels, for locating an edge of the wall portion located between the securing channel and the 10 casting cavity. Figure 5 illustrates a casting element 501 with locating channels for the wall portions arranged either side. At one side, die outer wall of the channel includes a chamfering portion 505. At the other side, the outer wall 503 of the channel is a plain blank wall. Again, the chanifered concrete panel 526 ends up having steps 530 resulting from the radiusing 531 of the 15 leading edge of the chamfering portion 505. Similarly, concrete component 540 includes stepbacks 548 resulting from the thickness 550 of the plain walls 503. Figures 10 and 11 illustrate preferred embodiment of the present invention, although variations in the form of the casting element are expected, for example, the casting elements may 20 include different chamfering shapes and dimensions, chamfering portions on both sides, one side or no sides, and the securing channel of the casting element of Figure 11 may take any suitable form. According to the present invention, and as illustrated in Figures 10 and 11, the board or wall portion has a side face including a stepback along the length of the board or wall portion 25 adjacent the edge of the wall portion to be inserted in the channel of the casting element. Thus the side face of the board includes a first planar portion 110 separated from the board edge 112 by a stepback 114. The width of the stepback 114 (the distance between the step 116 and the edge 112) is approximately equal to, but preferably slightly less than, the depth of the channel formed by the inside face 118 of the outer wall of the channel. So when the edge portion of the 30 board or wall portion is fitted fully into the channel, the step 116 butts against the leading edge 120 of the chamfering portion. The depth of the stepback (or the height of the step 116) matches the radiusing or thickness of the edge 120 so that the planar portion 110 of the face of the wall portion comes together with the outward face 135 of the chanfering portion at an edge 136 without a step. The resulting concrete product 119 includes an end face 125 and a chamfer 35 127 which meet along an edge 129 that does not include a step. Similarly, where the wall portion -i377757_tDoc 11 of board is used in conjunction with a plain walled channel, the step 116 matches the thickness 130 of the outer plain wall 132 such that the first planar portion 140 of the wall portion meets the outer face of the plain wall 132 without a step between them. Accordingly, the cast concrete component 141 includes a plain edge 143 that does not include any step. 5 It would be appreciated that onec of the benefits of implementing the wall portions according to the present invention is that the concrete components can be formed using the modular casting system without the concrete components having a resulting step at the formed edges. Resulting from this, the casting element may also be modified slightly to include a greater radius at the entry to the channel that holds the edge of the wall portion or board, making it 10 easier to assemble the formwork. The stepback along each face of the wall portion or board may be formed, for example, by rebating along the edge of the board using a suitable router or plane, or by laminating a narrower face portion to a wider board, or by forming the wall portion or board directly with the required profile (for example using a spindle moulder In fishing the wooden board or extruding the 15 required profile in the case of a plastic or aluminium wall portion). The stepback may be provided along both edges of a single face of a wall portion (as illustrated in Figure 11). The stepback may be provided along both edges of both faces of the wall portion, for example, as illustrated in Figure 10. ,l77?7 i 7 O