TECHNICAL FIELD

[0001] The present disclosure relates to a joint and a system for a joint. In particular, although not exclusively, the present disclosure relates to steel structures which could be the framework of a portal system, rafter system for a building, or any other structural element.

BACKGROUND

[0002] There are several ways to make buildings using steel, or at least with a steel substructure. These buildings are typically constructed from a lightweight channel or C section frame, and the frames are joined at intersecting points by a range of fasteners and brackets.

[0003] United States patent US 2005/0120658 A1 discloses a joint structure for a building using thin and lightweight shaped-steel. It discloses a joint structure for fastening and fixing frame members made of thin lightweight shaped-steel to steel sills and a bolt joint truss structure for forming a main structure of a roof. This joint structure is also used to fasten a steel frame member to form a wall to a steel floor sill. The joint portions of the respective members are connected together to form a joint and a fastener is inserted into the joint through-hole to fasten and fix the respective members to each other.

[0004] Japanese patent JP 2004/346614 A2 discloses a joint structure of steel column or steel pipe column and beam reinforcement. The document discloses a joint bracket for screw reinforcement fixed to a reinforcement fixation position on an outer face of a column flange of the crisscross steel frame column, and a tip of a beam reinforcement composed of the screw reinforcement is screwed into the joint bracket to join the beam reinforcement with the crisscross steel frame column.

[0005] United States patent US 6,920,724 discloses a bracket for a structural panel and a structural panel made with such a bracket. The bracket for use in fabricating steel structural panels has a first passageway for accepting a connecting member secured to a diametrically opposed bracket to introduce tension between opposing brackets in the panel. The brackets each have an additional second passageway to accept a connecting member for securing the brackets to a horizontal structural slab or other floor systems.

[0006] United States patent US 6,047,513 relates to a construction system for building a steel frame using steel members. Rafters form a roof portion of the steel frame, and a ceiling joist having two ends form a ceiling portion of the steel frame. Compression webs and tension webs, disposed between the rafters and the ceiling joists, distribute the load between the rafters and the ceiling joists. A peak bracket connects two rafters and a compression web together. Eave brackets connect the two unconnected ends of the two connected rafters to the ends of the ceiling joist. Compression brackets connect the pressure webs to the ceiling joist. A centre bracket connects two of the tension webs and one of the compression webs to the ceiling joist. Channel brackets connect one of the tension webs and one of the compression webs to one of the rafters and the ceiling joist.

[0007] Although the above existing systems work well from a structural perspective, there are a number of disadvantages associated with the use of additional brackets and fasteners to join the steel sub structures.

[0008] From an operational perspective, it can be difficult for a business to supply complete building systems. Currently, the joining brackets and roll formed steel sections to be joined are manufactured by alternative suppliers. This is because the range of machinery required to produce the brackets and sections is vastly different, making the consolidation of supply uneconomic from an investment perspective.

[0009] Conventional engineering design in most cases also calls for the brackets securing the joints of the steel sections to be twice as thick as the base frame material. This leads to higher costs as steel is sold by weight.

[0010] As the joining brackets and the steel sections are made from different steels, or materials then they will expand and contract at different rates. This may induce stress and/or loosen connections between the section and the bracket.

[0011] The requirement of present steel framing systems for large scale constructions to have both the brackets and the steel sections means that designing and specifying a building adds complexity. The steel sections must be designed to work with specific bracket systems. If these brackets have an issue with supply then this can set a building project back in time until the brackets can be supplied. Further, if the specific bracket system cannot be supplied for whatever reason, then at best a new bracket system must be sourced with its own lead times etc. If this new bracket system differs from the old one, then the steel structure that has been designed will have to be redesigned and possibly re-engineered and certified. This is worse still if steel sections have been cut and prepared. They will have to be reworked or worse scrapped and started again.

[0012] Having to assemble steel structures that then need additional separate brackets held in place and attached leads to cost and handling issues. The steel structures may need bracing, or other support until the brackets are attached to the steel structure, or between the structures. This leads to increased handling of multiple components, the steel sections and the brackets, as well as more components on site. Having additional components can also lead to incorrect assembly. Every time there is a separate, or another, component then this adds to cost with handling, freight and assembly.

[0013] Further, if for any reason a geometry, for example of two steel sections that are to be joined, is outside the capabilities of a chosen bracket system, then either this geometry cannot be achieved, leading to redesign, or a different bracket, outside the chosen bracket system, must be used. This adds to longer design, specifying and certifying times, as well as obtaining additional components from a different supplier.

[0014] The heavy nature of the conventionally designed brackets also adds additional freight expenses to the overall cost structure. This freight cost is from the supplier to the steel section fabricator, which adds cost, and then both the steel section and the brackets freighted to the job site.

[0015] As the brackets are required to be thicker than the base material and pre-galvanised material can only be purchased up to 3 mm thick, the majority of brackets also have to be galvanised after they are formed. This adds additional cost and time and potential delay to the process.

[0016] In most cases the design and distribution of light weight steel buildings is limited to a few key wholesalers who distribute their product by way of franchising the rights to smaller locally based individuals. The present number of brackets and the various construction techniques and practises create complexities. This requires constructors to undergo specific intensive training to bring them up to standard, again adding additional time and cost to the process. This also can limit the desired assembly geometries, as stated above, for the

[0017] In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

[0018] It is an object to provide an improved joint system for steel construction, or to provide an improved knee joint in steel that reduces the complexity of the components needed, or the component count, to reduce manufacturing time and complexity, as well as assembly, or to overcome the above shortcomings or address the above desiderata, or to at least provide the public with a useful choice.

SUMMARY

[0019] In a first aspect there is described a joint system for structural elements for a building construction, comprising a first beam of closed hollow cross-section having a cutout in at least one side of the beam to accommodate a second beam within the cutout, and a fastening system to attach both beams to each other.

[0020] In a further aspect there is described a joint system for structural elements for a building construction, comprising a first beam formed from at least two pieces of overlapping sheet steel to define a closed hollow cross-section, a second beam having a hollow cross-section, the first beam having at least two unitarily formed opposing extending portions having a distance between them to accommodate, when in a jointed condition, the second beam therebetween, the extending portions and the second beam each having a plurality of corresponding, when in a jointed condition, spaced apart holes to receive fasteners therethrough, such that when in a jointed and fastened condition the joint system provides a joint system that is moment, in plane, and out of plane, force resistant.

[0021] In a further aspect there is described a joint system for structural elements for a building construction, comprising a first beam, extending in a first direction, of hollow cross-section formed from a first two pieces of sheet steel, the first two pieces of sheet steel overlapping each other at least in part to form the hollow cross-sectional, a second beam, extending in a second direction, of closed hollow cross-section formed from a second two pieces of sheet steel, the second two pieces of sheet steel overlapping each other at least in part to form the closed hollow cross-sectional, the second beam having a first dimension perpendicular to the second direction, the first beam having two opposing extending portions unitarily formed by at least one of the first two pieces of steel, the extending portions having a distance between them substantially equal to the first dimension of the second beam, the extending portions and the remainder of the first two pieces of sheet steel providing between them a complimentary pocket for the second beam, the extending portions each having a first plurality of spaced apart holes thereon to receive fasteners therethrough, the second beam having a second plurality of spaced apart holes on opposing sides thereof to receive the same fasteners therethrough, complimentary to the first plurality, wherein locating the second beam into the complimentary pocket of the first beam, and locating fasteners through the first plurality of spaced apart holes, and second plurality of spaced apart holes provides a jointed beam that is moment, in plane, and out of plane, force resistant.

[0022] In a further aspect there is described a joint system for structural elements for a building construction, comprising a first beam formed from at least two pieces of overlapping sheet steel to define a closed hollow cross-section, a second beam having a hollow cross-section, the first beam having at least two unitarily formed opposing extending portions having a distance between them to accommodate, when in a jointed condition, the second beam therebetween, the extending portions and the second beam each having a plurality of corresponding, when in a jointed condition, spaced apart holes to receive fasteners therethrough, such that when in a jointed and fastened condition the joint system provides a joint system that is moment, in plane, and out of plane, force resistant, and wherein the extending portions are formed from at least one of the at least two pieces of overlapping sheet steel that define the closed hollow cross-section beam. [0023] In a further aspect there is described a method of forming a joint system for structural elements for a building construction, comprising providing a first beam, extending in a first direction, of hollow cross-section formed from a first two pieces of sheet steel, the first two pieces of sheet steel overlapping each other at least in part to form the hollow cross-sectional, the hollow cross-sectional being fully enclosed about the first direction, providing a second beam, extending in a second direction, of hollow cross-section formed from a second two pieces of sheet steel, the second two pieces of sheet steel overlapping each other at least in part to form the hollow cross-sectional, the hollow cross-sectional being fully enclosed about the second direction, the second beam having a first dimension perpendicular to the second direction, the first beam having integral unitary extensions of the hollow cross-sectional that form two parallel extensions, the two parallel extensions having a distance between them substantially equal to the first dimension of the second beam, the two parallel extension and the remainder of the first two pieces of sheet steel providing between them a complimentary pocket for the second beam, the two parallel extensions each having a first plurality of spaced apart holes thereon to receive fasteners therethrough, the second beam having a second plurality of spaced apart holes on opposing sides thereof to receive the same fasteners therethrough, complimentary to the first plurality, locating the second beam into the complimentary pocket of the first beam, and locating fasteners through the first plurality of spaced apart holes, and second plurality of spaced apart holes provides a jointed beam that is moment, in plane, and out of plane, force resistant.

[0024] In a further aspect there is described a method of manufacturing a first beam to receive a second beam, the second beam to extend in a second direction, the first beam to extend in a first direction, comprising the first beam formed from two nested pieces of sheet steel, having at least one end, integral unitary extending portions of at least one of the two pieces of sheet steel that form two parallel opposing extending portions, the extending portions having a distance between their inner facing surfaces substantially equal to a first dimension of the second beam, the two extending portions and the remainder of the first two pieces of sheet steel providing between them a complimentary pocket for the second beam, the two extending portions each having a first plurality of spaced apart holes thereon to receive fasteners therethrough, the second beam capable of being received by the second beam and fastened thereto to form a jointed beam that is moment, in plane, and out of plane, force resistant.

[0025] In a further aspect there is described a kit of parts for forming a joint between a second beam and a first beam, comprising a first beam, extending in a first direction, of hollow cross-section formed from a first two pieces of sheet steel, the first two pieces of sheet steel overlapping each other at least in part to form the hollow cross-sectional, a second beam, extending in a second direction, of closed hollow cross-section formed from a second two pieces of sheet steel, the second two pieces of sheet steel overlapping each other at least in part to form the closed hollow cross-sectional, the second beam having a first dimension perpendicular to the second direction, the first beam having two opposing extending portions unitarily formed by at least one of the second two pieces of steel, the extending portions having a distance between them substantially equal to the first dimension of the second beam, the extending portions and the remainder of the first two pieces of sheet steel providing between them a complimentary pocket for the second beam, the extending portions each having a first plurality of spaced apart holes thereon to receive fasteners therethrough, the second beam having a second plurality of spaced apart holes on opposing sides thereof to receive the same fasteners therethrough, complimentary to the first plurality, a plurality of fasteners to engage between the first plurality of spaced apart holes and their corresponding second plurality of spaced apart holes, such the second beam and the first beam may be fastened together using the fasteners to form a jointed beam that is moment, in plane, and out of plane, force resistant.

[0026] In a further aspect there is described a joint system as described herein with reference to any one or more of the accompanying drawings.

[0027] In a further aspect there is described a method of forming a joint system as described herein with reference to any one or more of the accompanying drawings.

[0028] In a further aspect there is described a method of manufacturing a first beam to receive a second beam as described herein with reference to any one or more of the accompanying drawings.

[0029] In a further aspect there is described a kit of parts for forming a joint between a second beam and a first beam as described herein with reference to any one or more of the accompanying drawings.

[0030] In a further aspect there is described a construction including a joint system as described herein with reference to any one or more of the accompanying drawings.

[0031] Any one or more of the following embodiments may relate to any of the aspects described herein or any combination thereof.

[0032] In one configuration the second beam is formed from at least two pieces of overlapping sheet steel to define a closed hollow cross-section.

[0033] In one configuration an extending portion is formed from at least two of the two pieces of overlapping sheet steel that define the closed hollow cross-section. [0034] In one configuration an extending portion is formed from both of the first two pieces of steel.

[0035] In one configuration the pieces of overlapping sheet steel are formed into the respective first and/or second beam by any one or more of

• roll forming,

• folding, or

• cold forming.

[0036] In one configuration the extending portions are cut into the second one or two pieces of steel prior to forming the first beam.

[0037] In one configuration the extending portions are formed by cutting the first beam after the first beam is formed into a closed hollow cross-sectional beam.

[0038] In one configuration two opposing extending portions are parallel to each other.

[0039] In one configuration two opposing extending portions each present planar inward facing surfaces that in part define a complimentary pocket.

[0040] In one configuration a substantial length of the first and/or second beam have an enclosed cross-sectional.

[0041] In one configuration the first and second beams are of constant cross-sectional along their length.

[0042] In one configuration the closed hollow cross-sectional beam is of rectangular or square cross-sectional.

[0043] In one configuration the closed hollow cross-sectional beam is of rectangular cross- sectional.

[0044] In one configuration at least one of the extending portions includes at least one reinforcing rib formed onto the exterior surface of the extending portion.

[0045] In one configuration the one or more reinforcing ribs running parallel to the main axis of the first beam.

[0046] In one configuration the reinforcing ribs extend from the extending portions into the body of the first beam. [0047] In one configuration the second beam has threaded connections complimentary to the second plurality of spaced apart holes, inward of an external surface of the second beam, to receive and engage the fasteners there into.

[0048] In one configuration the second two pieces of sheet steel and first two pieces of sheet steel are between 2, 3, 4, 5, 6, 7, 8, 9, or 10 mm thick, and suitable ranges may be selected from between any of these values.

[0049] In one configuration second two pieces of sheet steel and first two pieces of sheet steel are about 6 mm thick.

[0050] In one configuration the closed hollow cross-sectional beam(s) are formed from first and second open cross-sectional beams that are nested, one inside the other.

[0051] In one configuration the first and second open cross-sectional beams are held relative to each other substantially by friction.

[0052] In one configuration there is at least some local deformation of the first or second open cross-sectional beams to hold the two relative to each other.

[0053] In one configuration the closed hollow cross-sectional has two opposed vertical webs, and two opposed horizontal flanges connecting therebetween.

[0054] In one configuration the first open cross-sectional beam forms a first of the vertical webs and part of a second of the vertical webs, and the second open cross-sectional beam forms the second vertical web, and part of the first vertical web, the first open cross-sectional beam and the second open cross-sectional beam both forming the two opposed horizontal flanges.

[0055] In one configuration an open part of the complimentary pocket from the closed hollow cross-sectional is substantially closed off by a first blanking plate

[0056] In one configuration an open end of the second beam near the complimentary pocket is substantially closed off by a second blanking plate.

[0057] In one configuration the open part and open end are closed off by plate steel 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13 14, or 15 mm thick, and suitable ranges may be selected from between any of these values.

[0058] In one configuration the open part and open end are closed off by plate steel about 10 mm thick.

[0059] In one configuration the sheet steel of the first and second beam are joined, to form the respective first and second beam, by welding. [0060] In one configuration the open part and open end are closed off by plate steel that is welded to its respective beam sheet steel.

[0061] In one configuration there is no separate bracket between the second beam and the first beam.

[0062] In one configuration the two parallel extensions are formed from sheet steel of the first beam.

[0063] In one configuration the first and second beams are load-carrying members of a portal frame.

[0064] In one configuration the complimentary pocket is formed as part of forming the first beam and is not cut from the beam after it is formed.

[0065] In one configuration the complimentary pocket is formed from the first beam by cutting the first beam after it is formed.

[0066] In one configuration the extending portions are formed in the one or two pieces of sheet steel prior to forming the first beam.

[0067] In one configuration the extending portions are formed in the one or two pieces of sheet steel after the first beam is formed.

[0068] As used herein the term “and/or” means “and” or “or”, or both.

[0069] As used herein “(s)” following a noun means the plural and/or singular forms of the noun.

[0070] The term “comprising” as used in this specification means “consisting at least in part of”. When interpreting statements in this specification which include that term, the features, prefaced by that term in each statement, all need to be present, but other features can also be present. Related terms such as “comprise” and “comprised” are to be interpreted in the same manner.

[0071] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1 , 1 .1 , 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1 .5 to 5.5 and 3.1 to 4.7).

[0072] This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements and features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. [0073] 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

[0074] Figure 1 shows an isometric view of a column with one half of the connection.

[0075] Figure 2 shows an isometric view of a rafter with one half of the connection, being complimentary to that shown in Figure 1 .

[0076] Figure 3 shows various configurations of open cross sectional steel to form the closed cross sectional beam as described.

[0077] Figure 4 shows in side isometric view of the connection as described applied to a floor joist and column.

[0078] Figure 5 shows in side isometric view of the connection as described applied to a rafter and column.

[0079] Figure 6 shows Section AA along line A-A from Figure 5.

[0080] Figure 7 shows a typical construction using steel sheet and the potential locations of the joint as described, for example as a floor joist and as a rafter.

DETAILED DESCRIPTION

[0081] Described is a joint system for structural elements for a building construction, comprising a first beam of closed hollow cross-section having a cutout in at least one side of the beam to accommodate a second beam within the cutout, and a fastening system to attach both beams to each other.

[0082] A joint 1 for a jointed beam is shown in Figures 4 and 5. The joint 1 may be used in the construction of steel frame buildings as shown in Figure 7. For example, the joint 1 may be used to form the framework of a portal system, rafter system for a building, or any other structural element.

[0083] The joint 1 is formed from a first beam 8 and a second beam 3. The first beam extends in a first direction 9 and the second beam 3 extends in a second direction 4. In the assembly of the two beams shown the second direction 4 and the first direction 9 are different, and the joint 1 that is formed is for example a knee joint where the first beam 8 is vertical or near vertical and supports the second beam which extends out from the first beam 3, to form, for example, a rafter. However, in other forms the second direction 4 and the first direction 9 may be the same, whether vertical as a post, or at an angle as a rafter, or horizontal as a joist. [0084] The first beam 8 and the second beam 3 may be formed by any one of roll forming, folding, or other cold or hot forming techniques.

[0085] The first beam 8 and the second beam 3 as shown in Figures 1 and 2 may be formed from two separate pieces of steel: 10A and 10B, and 5A and 5B. Each piece of steel may be formed as separate open cross-sectional beams having at least one vertical web and at least one horizontal web. The pieces of steel may be formed together to form a hollow cross sectional beam. As shown in Figures 3A to 3F a range of configurations of steel web combinations could be utilised. For example, in Figure 3A each piece of steel includes two full horizontal webs and one full vertical web. Each piece of steel are mirror images of each other, although one is nested within the other. The resultant beam has a closed cross-section. Figure 3B shows a cross-sectional beam formed from two separate pieces of steel, each piece having a full vertical web and two full horizonal webs. The two pieces of steel are mirror images, with the cross-sectional beam formed by each piece of steel having one horizontal web located within the cross-section of the other piece of steel. Figure 3C shows a cross-sectional beam formed from two separate pieces of steel, each piece having a full vertical web, two partial vertical webs and two full horizonal webs. The two pieces of steel are nested in each other to form the hollow cross-sectional beam. Figure 3D shows a cross-sectional beam formed from two separate pieces of steel, each piece having two full vertical webs and one full horizonal web. One of the pieces of steel is fully nested in the other. Figure 3E shows a cross-sectional beam formed from two separate pieces of steel, each piece having two full vertical webs and one full horizonal web. The pieces of steel are mirror images of each other, each having one vertical web nested within the cross section of the other steel piece. Figure 3F shows a cross-sectional beam formed from two separate pieces of steel, each piece having one full vertical web and one partial vertical web and one full horizonal web. The pieces of steel are mirror images of each other, each having one vertical web nested within the cross section of the other steel piece.

[0086] Figure 2 shows a cross-sectional beam formed from two separate pieces of steel, each piece having one full vertical web, one partial vertical web, and two full horizonal webs. The pieces of steel are mirror images of each other, each having one vertical web nested within the cross section of the other steel piece. In doing so the two open cross-sectional pieces of steel form the beam 3 having a closed cross-sectional shown in Figure 1 . The resulting beam has a first dimension 7 across the webs as shown and is substantially rectangular in cross-sectional orthogonal to the second direction. It will be appreciate that the beam may be square or of other polygonal cross-sectional as needed, and potentially may be circular or ovoid.

[0087] As shown in Figure 2, the opposing sides 17 of the second beam 3 have a first plurality of spaced apart holes 14, these holes in the preferred form a threaded to receive a like threaded fastener 15. If the holes 14 themselves are not threaded then they may thread inserts or similar to receive the fasteners. [0088] To impart additional stiffness, or at least to prevent ingress of vermin and similar, the end of the second beam 3 may include a blanking plate 19 to close the end off.

[0089] The first beam 8, shown in Figure 1 similar to the second beam, is formed from two second pieces of steel 10A and 10B and may be formed of various cross sectional shapes as described above and shown in Figure 3. The open end of the hollow cross-section mean may be closed with a blanking plate 19 to enclose at least that end of the beam.

[0090] As shown in Figure 1 , the first beam 8 comprise two extending portions 11 . These may be formed unitary with the beam and are extensions of the two steel pieces 10A and/or 10B. As shown in Figure 1 , the extending portions 11 are formed from both steel pieces 10A and 10B - that is, one is formed from steel piece 10A, and the opposing one is formed from steel piece 10B. The extending portions may comprise reinforcing ribs 20 as shown in Figure 1 . The reinforcing ribs 20 may be located on their external surface of the extending portions 11 . The reinforcing ribs 20 may be located on the edge, or at least towards the edge, of the extending portions 11 . The ribs 20 may extend from the free end of the extending portion down into the full enclosed beam section. The planar inward facing surfaces 18 of the extending portions may the first dimension 7 of the second beam and are complimentary to these opposing sides 17. In this way when the fasteners are done up there is little movement of the extending portions 11 to support and engage the second beam 3.

[0091] The extending portions 11 may extend a distance that substantially matches the height of the second beam 3. As shown in Figure 4 the lengths of the extending portions 11 extend a majority of the height of the second beam. The extending portions 11 may extend at least 75, 80, 85, 90 or 95% of the height of the second beam, and useful ranges may be selected between any of these values.

[0092] The extending portions 11 may be unitary with the two pieces of steel 10A and 10B. They may be formed by cuts in the sheet steel that forms the open cross-sectional beams 24 prior to forming the first beam 8, for example using a three dimensional machine in flat form. The cuts are at the correct angle to form the complimentary pocket 13 to support the second beam 3.

[0093] Alternatively, lengths of beam may be made and then the complimentary pocket 13 is cut into the end of the beam section after forming to form the complimentary pocket 13, for example, but not limited to using a five axis robotic arm or similar and cutting tool. In doing so the webs of the beam are cut away at the correct angle and to form the support surface 25 to match the second beam angle.

[0094] The free end of the hollow cross-sectional of the beam 8 may be angled to match the angle of incidence of the second beam 3 to the first beam as seen in Figure 3. This provides clearance, but also when closely matched will provide a support surface 25 to the facing surface of the second beam 3. When keyed into place with the fasteners this may also provide resistance against moments. The result is a complimentary pocket 13 in the first beam 8 that can receive the second beam 3. [0095] The extending portions 11 have the second plurality of spaced apart holes 16 which are complimentary to those of the second beam 3. When the second beam is located in the complimentary pocket 13, either with additional support, or by the support surface, then the holes will align and then fasteners 15 can be passed through the second plurality 16 and engage with the first plurality 14. If these are threaded fasteners then torqueing them up will form the joint as shown in Figure 4. In the preferred form these are hollow bolts as the threaded connection.

[0096] The first two pieces of steel 5A and 5B and the second two pieces of steel 10A and 10B may be formed from sheet steel. The sheet steel may be 2, 3, 4, 5, 6, 7, 8, 9, or 10 mm thick, and useful ranges may be selected between any of these values. In one embodiment the sheet steel is 6 mm thick. The blanking plate 19 may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14 or 15 mm thick, and useful ranges may be selected between any of these values. In one configuration the blanking plate is 10 mm thick.

[0097] Although embodiments have been described with reference to a number of illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention as herein described with reference to the accompanying drawings.