[0001]    The present invention relates to a halving joint structure, and particularly, but not exclusively, to a halving joint structure which improves the strength and rigidity of the joint. 
       BACKGROUND 
       [0002]    A conventional halving joint is created by forming a slot in opposite edges of a first member and a second member, which are to be joined. Commonly, the slots formed in the first and second member are of equal length and the slots extend half of the way through the thickness of each member. However, if the members are of differing thicknesses, only one of the slots may extend half of the way through the thickness of the member. 
         [0003]    The two members are arranged perpendicularly and the slot of one member is introduced into the slot of the other member until a bottom surface of the slot of the first member contacts a bottom surface of the slot of the second member. This forms an overlapping interconnection between the two members. Where the slots of the first and second members are of equal length and extend half of the way through the thickness of each member, the edges of the first and second members align to form a continuous connection. 
         [0004]    The conventional halving joint is simple to manufacture and assemble, and is therefore widely used. The conventional halving joint is usually created with wooden members, but can also be formed from cardboard, plastic or metal members (particularly sheet metal). A plurality of members each having a plurality of slots can be used to form a grid-type arrangement. This is particularly useful for forming compartments, for example, for packaging. 
         [0005]    However, the conventional halving joint is relatively weak and the first and second members may become misaligned easily. Furthermore, the joint can be easily separated, which in certain applications is undesirable. Where the members are formed from metal, this can be prevented by welding the first and second members together. However, welding causes distortion of the members, and also increases the cost and lead-time of the component. Furthermore, it is then not possible to separate the joint if desired. Alternatively, the first and second members may be connected using rivets or bolts. Rivets provide a semi-permanent connection but they add significantly to the parts-count of the component and again increase the cost and lead-time of the component. Although bolts provide a disassemblable connection, they also increase the parts-count, cost and lead-time of the component. 
         [0006]    The present invention seeks to provide a halving joint structure which solves some or all of the problems associated with the conventional halving joint described above. 
       STATEMENTS OF INVENTION 
       [0007]    In accordance with an aspect of the invention, there is provided a halving joint structure comprising: a first member and a second member couplable to one another in a nonparallel arrangement by a halving joint, wherein each of the first and second members has a joint slot for receiving a portion of the other of the first and second members to form the halving joint; wherein the first and second members have cooperating locking slots, the locking slot of the first member intersecting the joint slot of the first member, and the locking slot of the second member being formed in the portion of the second member which is received by the joint slot of the first member; the structure further comprising: a locking member which is receivable within the locking slots of the first and second members. 
         [0008]    The halving joint structure in accordance with the present invention increases the parts-count by just one part, the locking member. The locking member may be a simple component which can be lightweight and may be easily assembled and disassembled. Furthermore, the locking member may be formed using the same processes as used for the first and second members (e.g. laser cutting) and the halving joint structure may not require any further preparation before assembly. Consequently, the present invention does not add significantly to the cost and lead-time of the halving joint structure. 
         [0009]    The locking slots of the first and second members may lie in the same plane when the first and second members are coupled to one another. 
         [0010]    The locking slot of the first member may be perpendicular to the joint slot. 
         [0011]    The locking member may be a locking plate. 
         [0012]    The locking member may have a retaining portion which may be movable between a first configuration which allows the locking member to be received within the locking slots of the first and second members and a second configuration which prevents the locking member from being withdrawn from the locking slots of the first and second members. 
         [0013]    The retaining portion may lie in the plane of the locking slots when in the first configuration and may be out of the plane of the locking slots when in the second configuration. 
         [0014]    The retaining portion may be deformable between the first and second configurations. 
         [0015]    The retaining portion may be bendable between the first and second configurations. 
         [0016]    The retaining portion may comprise a pair of bendable retaining arms. 
         [0017]    The locking member may comprise a head portion. 
         [0018]    The head portion may have an extraction hole. The extraction hole may provide an attachment point for gripping the locking member to aid in removing the locking member from the locking slots. 
         [0019]    The locking member may be adapted to maintain the nonparallel arrangement of the first and second members. 
         [0020]    The head portion may be sized to maintain the nonparallel arrangement of the first and second members. 
         [0021]    The retaining portion may be sized to maintain the nonparallel arrangement of the first and second members. 
         [0022]    The retaining portion may be sized to maintain the nonparallel arrangement of the first and second members when in the second configuration. 
         [0023]    The first member, second member, and/or locking member may be metal. 
         [0024]    The first member, second member, and/or locking member may be formed from sheet metal. 
         [0025]    The first and second members may have additional cooperating locking slots, the additional locking slot of the second member intersecting the joint slot of the second member, and the additional locking slot of the first member being formed in the portion of the first member which is received by the joint slot of the second member; and the structure may further comprise: an additional locking member which is receivable within the additional locking slots of the first and second members. 
         [0026]    In accordance with another aspect of the invention, there is provided a locking member for a halving joint structure comprising a first member and a second member couplable to one another in a nonparallel arrangement by a halving joint, wherein each of the first and second members has a joint slot for receiving a portion of the other of the first and second members to form the halving joint; wherein the first and second members have cooperating locking slots, the locking slot of the first member intersecting the joint slot of the first member, and the locking slot of the second member being formed in the portion of the second member which is received by the joint slot of the first member; wherein the locking member is adapted to be received within the locking slots of the first and second members. 
         [0027]    In accordance with another aspect of the invention, there is provided a method of assembling a halving joint structure, the method comprising: providing a first member and a second member, each having a slot for receiving a portion of the other of the first and second members; wherein the first and second members have cooperating locking slots, the locking slot of the first member intersecting the joint slot of the first member, and the locking slot of the second member being formed in the portion of the second member which is received by the joint slot of the first member; inserting the portion of the first or second member into the slot of the other of the first and second members to form a halving joint, with the first and second members in a nonparallel arrangement; and inserting a locking member into the locking slots of the first and second members. 
         [0028]    The method may further comprise moving a retaining portion of the locking member from a first configuration which allows the locking member to be received within the locking slots of the first and second members to a second configuration which prevents the locking member from being withdrawn from the locking slots of the first and second members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
           [0030]      FIG. 1  is a perspective view of a halving joint structure according to an embodiment of the invention, prior to assembly; 
           [0031]      FIG. 2  is a top view of a locking member of the halving joint structure; 
           [0032]      FIG. 3  is a perspective view of the assembled halving joint structure; 
           [0033]      FIG. 4  is a perspective view of the assembled halving joint structure showing the locking member in a first unlocked configuration; and 
           [0034]      FIG. 5  is a perspective view of the assembled halving joint structure showing the locking member in a second locked configuration. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    With reference to  FIG. 1 , a halving joint structure according to embodiment of the invention is formed by a first member  2  and a second member  4 . The first and second members  2 ,  4  are constructed from sheet metal. 
         [0036]    A joint slot  6   a  is formed in the first member  2  and a joint slot  6   b  is formed in the second member  4 . The joint slots  6   a ,  6   b  extend perpendicularly from opposite edges of the first and second members  2 ,  4 . The joint slots  6   a ,  6   b  of the first and second members  2 ,  4  widen at a bottom end to form a bulbous portion  8   a ,  8   b  having a flat bottom surface  10   a ,  10   b.    
         [0037]    A locking slot  12   a  is formed in the first member  2 . The locking slot  12   a  of the first member  2  is located along the length of the joint slot  6   a  and extends perpendicularly to the joint slot  6   a . The locking slot  12   a  is arranged so that the joint slot  6   a  is at its centre. Accordingly, the joint slot  6   a  and locking slot  12   a  are in the shape of a cruciform. 
         [0038]    The second member  4  is also provided with a locking slot  12   b . Unlike the locking slot  12   a  of the first member  2 , the locking slot  12   b  of the second member  4  is remote from the joint slot  6   b  and is located in a portion  14   b  between the bottom surface  10   b  of the joint slot  6   b  and an opposite edge of the second member  4 . 
         [0039]    As indicated in  FIG. 1 , the first member  2  and second member  4  are introduced to one another with the first member  2  arranged perpendicularly to the second member  4  (i.e. rotated 90 degrees about an axis running along the joint slot  6   a ). The first and second members  2 ,  4  are urged towards one another with the joint slots  6   a ,  6   b  in alignment until the bottom surface  10   a  of the slot  6   a  of the first member  2  contacts the bottom surface  10   b  of the slot  6   b  of the second member  4 . Accordingly, the portion  14   b  of the second member is received within the joint slot  6   a  of the first member  2  and a corresponding portion  14   a  of the first member  2  is received within the joint slot  6   b  of the second member  4 . 
         [0040]    In this position, the locking slots  12   a ,  12   b  of the first and second members are located so that they are aligned and lie in the same plane. Consequently, the locking slots  12   a ,  12   b  are arranged so as to allow a locking member  16  to pass through the locking slots  12   a ,  12   b.    
         [0041]    As shown in  FIG. 2 , the locking member  16  is a flat elongate plate of sheet metal which comprises a head portion  18  at one end and a retaining portion  20  at the other end. 
         [0042]    The head portion  18  of the locking member  16  comprises an extraction hole  20  which passes through the head portion  18 . The head portion  18  further comprises a pair of shoulders  22   a ,  22   b  on either side of the head portion  18 , and which are separated from one another by the extraction hole  20 . The shoulders  22   a ,  22   b  protrude from the locking member  16  and define the head portion  18 , which is wider than the remainder of the locking member  16 . 
         [0043]    The retaining portion  20  of the locking member  16  comprises a pair of slits  24   a ,  24   b  which extend from either side of the retaining portion  20  into the body of the locking member  16 . The slits  24   a ,  24   b  are angled towards the head portion  18 . The slits  24   a ,  24   b  are separated by an indentation  26  which is formed in the retaining portion  20  and extends towards the head portion  18  of the locking member  16 . The indentation  26  defines a pair of retaining arms  28   a ,  28   b  located on either side of the indentation  26 . The retaining arms  28   a ,  28   b  are separated from the remainder of the locking member  16  by the slits  24   a ,  24   b . This allows the retaining arms  28   a ,  28   b  to be bent out of the plane of the remainder of the locking member  16 , as will be described in further detail below. 
         [0044]    As shown in  FIG. 3 , when the bottom surfaces  10   a ,  10   b  contact one another, the edges of the first and second members  2 ,  4  are in alignment. 
         [0045]    The coupled first and second members  2 ,  4  define four quadrants  30 ,  32 ,  34 ,  36  and the slots  12   a ,  12   b  define a passage through the first and second members  2 ,  4  from one of the four quadrants to an opposite quadrant i.e. from quadrant  30  to quadrant  34 , for example. The width of the passage through the first and second members  2 ,  4  is defined by the distance across a quadrant from an edge of the locking slot  12   a  of the first member  2  to an edge of the locking slot  12   b  of the second member  4 . Accordingly, where the first and second members  2 ,  4  are in a perpendicular arrangement, the width of the passage is equal to the hypotenuse of a triangle having two other sides which have a length that is approximately equal to half of the length of the locking slots  12   a ,  12   b.    
         [0046]    The locking member  16  is passed from the quadrant  30 , through the locking slots  12   a ,  12   b  with the retaining portion  20  leading, until the shoulders  22   a ,  22   b  of the head portion  18  contact the first and second members  2 ,  4  respectively in the quadrant  30 . The shoulders  22   a ,  22   b  of the head portion  18  contact the first and second members  2 ,  4  and thus maintain the angle between the first and second members  2 ,  4 . 
         [0047]    The width of the locking member  16  is such that it is just narrower than the width of the passage through the first and second members  2 ,  4 . Furthermore, the length of the locking member  16  is such that, with the shoulders  22   a ,  22   b  contacting the first and second members  2 ,  4  in the quadrant  30 , the slits  24   a ,  24   b  and the retaining arms  28   a ,  28   b  protrude into the opposite quadrant  34 , as shown in  FIG. 4 . 
         [0048]    As shown in  FIG. 5 , once the locking member  16  is received in the locking slots  12   a ,  12   b , the retaining arms  28   a ,  28   b  are bent down from the first unlocked configuration where they lie in the plane of the remainder to a second locked configuration where the retaining arms  28   a ,  28   b  are out of the plane of the remainder of the locking member  16  and, more importantly, out of the plane of the locking slots  12   a ,  12   b . This prevents the locking member  16  from being withdrawn from the locking slots  12   a ,  12   b . In the second locked configuration the retaining arms  28   b ,  28   a  contact the first and second members  2 ,  4  respectively in the opposite quadrant  34 . Similarly to the shoulders  22   a ,  22   b  of the head portion  18 , the retaining arms  28   a ,  28   b  contacting the first and second members  2 ,  4  helps to maintain the angle between the first and second members  2 ,  4 . 
         [0049]    To remove locking member  16 , the retaining arms  28   a ,  28   b  must be first bent from the second locked configuration back to the first unlocked configuration so that the retaining arms again lie in the plane of the locking slots  12   a ,  12   b . The locking member  16  may then be pulled out of the locking slots  12   a ,  12   b  using the extraction hole  20 . This allows the first and second members  2 ,  4  to be separated from one another when desired. The retaining arms  28   a ,  28   b  may move from the first unlocked configuration to the second locked configuration and back to the first unlocked configuration many times. 
         [0050]    Although the retaining arms  28   a ,  28   b  of the locking member  16  have been described and shown as being bent down from the plane of the remainder of the locking member  16 , they could alternatively be bent up from this plane. Furthermore, each retaining arm  28   a ,  28   b  could be bifurcated (akin to a split pin) to allow the retaining arms  28   a ,  28   b  to be bent both up and down. 
         [0051]    Furthermore, the retaining portion  20  may prevent the locking member  16  from being withdrawn from the locking slots  12   a ,  12   b  using alternative means. For example, the retaining portion  20  could have a portion which is twisted (i.e. about a longitudinal axis of the locking member  16 ) out of the plane of the locking slots  12   a ,  12   b  or which is pivoted out of the plane of the locking slots  12   a ,  12   b  and locked in position. Further still, the locking member  16  may have a portion which is deformed once the locking member  16  is inserted so that it is larger than the passage defined by the locking slots  12   a ,  12   b.    
         [0052]    Although only one pair of locking slots  12   a ,  12   b  has been described, further locking slots may be provided on the first and second members  2 ,  4 . For example, the first and second members  2 ,  4  may be provided with an additional pair of locking slots. The additional locking slots may be identical to the locking slots  12   a ,  12   b  but in the reversed configuration, whereby the additional locking slot of the first member is located in the portion  14   a  and the additional locking slot of the second member  4  is located along the length of the joint slot  6   b . An additional locking member  16  is provided which is received in the additional locking slots of the first and second members  2 ,  4 . Consequently, with this arrangement the first and second members  2 ,  4  are identical. Furthermore, each of the first and second members  2 ,  4  may comprise a plurality of joint slots  6   a ,  6   b , locking slots  12   a ,  12   b  and locking members  16  so as to allow the first and second members  2 ,  4  to form multiple halving joints with other members. This allows a grid-type arrangement to be formed. 
         [0053]    The first and second members  2 ,  4  do not necessarily need to be arranged perpendicularly to one another. The first and second members  2 ,  4  may be joined in any nonparallel arrangement. Furthermore, the locking slot  12   a  of the first member need not be perpendicular to the joint slot  6   a  of the first member. However, the locking slot  12   a  of the first member  2  must be angled with respect to joint slot  6   a  of the first member  2 . Further still, although the locking slots  12   a ,  12   b  of the first and second members  2 ,  4  have been described as lying in the same plane when the first and second members  2 ,  4  are coupled to one another, this need not be the case. For example, the locking slots  12   a ,  12   b  may be arcuate and receive a similarly arcuate locking member  16 . In this case, the locking slots  12   a ,  12   b  of the first and second members  2 ,  4  lie on a curved surface when the first and second members  2 ,  4  are coupled to one another. However, when the first and second members  2 ,  4  are coupled to one another, the locking slots  12   a ,  12   b  must be configured so as to allow a suitable locking member  16  to be received within the locking slots  12   a ,  12   b , thereby locking the first and second members  2 ,  4  together. 
         [0054]    Although the first and second members  2 ,  4  have been described as being constructed from sheet metal, they could be formed from alternative materials. Furthermore, where the base material of the locking member  16  is unsuitable for forming the retaining arms  28   a ,  28   b , metal (or other suitable material) retaining arms may be joined to the locking member  16 . 
         [0055]    The halving joint structure of the present invention may find particular applications in the aerospace industry. For example, the halving joint structure may be used to form ducts or other sheet metal structures. The halving joint structure of the present invention may be particularly useful for circular components.
A halving joint structure including: a first member and a second member couplable to one another in a nonparallel arrangement by a halving joint, wherein each of the first and second members has a joint slot for receiving a portion of the other of the first and second members to form the halving joint; wherein the first and second members have cooperating locking slots, the locking slot of the first member intersecting the joint slot of the first member, and the locking slot of the second member being formed in the portion of the second member which is received by the joint slot of the first member; the structure further including: a locking member which is receivable within the locking slots of the first and second members.