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TECHNICAL FIELD 
       [0001]    The present disclosure relates to dragline mining machines and particularly to a configuration of boom chord and lacing for dragline machines used in mining. 
       BACKGROUND 
       [0002]    Dragline machines use a large bucket suspended from a boom to move a payload, such as earth or ore, at a worksite. The boom for the dragline may be more than 400 feet long and has numerous weld joints that need routine inspection and periodically need repairs. The boom may be constructed of chords running the length of the boom and lacings that connect the chords with a series of geometric patterns, such as triangles, that provide support for the bucket and payload, as well as the boom itself. 
         [0003]    Tubular booms use round steel pipes for chords and lacings with the chords diameter being larger than the lacing diameter. Some lacings are perpendicular to the chords and some are at an angle. In both cases, the end of the lacing must be formed to match the round contour of the mating surface on the chord using a coping cut on the end of the lacing. Further, because the lacings often terminate in the same spot, the weld joints overlap. 
         [0004]    The closed interior of the chord pipe makes it difficult to inspect the back side of the weld joint. Further, overlapping weld joints at a particular attachment point on a chord make it difficult to inspect for damage to a weld or lacing. Overlapping weld joints also make repairs costly and time consuming because multiple lacings are affected each time one lacing is repaired or replaced. 
         [0005]    G.B. 523,571A (the &#39;571 patent), titled “Improvements in or relating to construction of Buildings” teaches the use of a formed metal plate in a truss with lacing supports that avoids coping cuts for lacing attachments. The &#39;571 patent uses formed metal across one entire side of the triangle-shaped structure. This adds weight and cost that would be unacceptable if applied to a boom structure. 
       SUMMARY OF THE DISCLOSURE 
       [0006]    In one aspect of the disclosure, a boom for a dragline machine includes a plurality of chords, each chord having a first mounting surface and a second mounting surface, the first and second mounting surfaces being planar and forming a reflex angle and the respective inside surfaces for the first and second mounting surfaces being planar and forming an obtuse angle. Each chord may be arranged so that at least one of the first and second mounting surfaces are facing and generally parallel with one mounting surface of another of the plurality of chords. A plurality of lacings may be used to couple respective facing mounting surfaces of the plurality of chords. 
         [0007]    In another aspect of the disclosure, a method of making a boom includes forming a metal plate into a chord having outside surfaces at a reflex angle and inside surfaces at an obtuse angle. The method includes forming additional chords from additional metal plates. The additional chords may have an identical cross section to the chord or may have a different shape from the chord. The chord and the additional chords may be coupled with lacing so that one outside surface of each chord faces a respective outside surface of one other chord. 
         [0008]    In yet another aspect of the disclosure, a boom for a dragline machine may include three chords, each chord made from a metal plate formed into three planar surfaces, each chord having at least one obtuse angle between adjacent planar surfaces. The boom may also include a plurality of inter-chord lacings made of pipes, each end of each inter-chord lacing lying in a single plane, wherein each lacing is attached between facing surfaces of two chords. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an illustration of a dragline machine; 
           [0010]      FIG. 2  is a perspective view of a portion of a boom of the dragline machine; 
           [0011]      FIG. 3  is a perspective view of a detail of the boom; 
           [0012]      FIG. 4A  is a perspective view of another detail of the boom; 
           [0013]      FIG. 4B  is a perspective view of an alternate embodiment of the boom detail of  FIG. 4A ; 
           [0014]      FIG. 5  is an end view of a section of the boom; 
           [0015]      FIG. 6  is an end view of an exemplary top chord of the boom; 
           [0016]      FIG. 7  is an end view of an exemplary side chord of the boom; 
           [0017]      FIG. 8  depicts attachment relationships between chords and lacings of an exemplary boom; and 
           [0018]      FIG. 9  is an end view of an alternate embodiment of the boom with four chords; 
           [0019]      FIG. 10  is a flowchart of a method of making a boom in accordance with the current disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  is a simplified illustration of a dragline machine  100 . The dragline machine  100  has a base  102  with an operator station  104 . The dragline machine  100  also has a boom  106  that is used to support a bucket  108 . The bucket  108  may be dragged along a work site surface  109  to collect and move material. 
         [0021]      FIG. 2  is a perspective view of the boom  106  of the dragline machine  100 . The boom  106  may include a first chord  110 , a second chord  112 , and a third chord  114 . In the illustrated embodiment, the first, or top, chord  110  has one shape and the second and third chords  112 ,  114 , are generally mirror images of each other and may be symmetric from a manufacturing perspective. In other embodiments, the boom  106  may have asymmetric chords. 
         [0022]    The chords  110 ,  112 ,  114  are connected using inter-chord lacings. For example, lacing  116  and lacing  120  are perpendicular inter-chord lacings. Inter-chord lacings  118  and  118   a  are oblique inter-chord lacings. Internal lacings  122 ,  124 ,  126  are connected in whole or in part to other lacings. In the illustrated embodiment, each internal lacing  122 ,  124 ,  126  is coupled at one end to one of the chords  110 ,  112 ,  114  and at the other end to another lacing  120 . 
         [0023]    Supports  128  and  130  are disposed along inside surfaces of the chords  110  and  112 ,  114  respectively and are formed to match the interior regions of their respective chords  110  and  114 , as shown in more detail in  FIGS. 6 and 7 . The supports  128  and  130  may be disposed either at points opposite where lacings are attached or may be attached anywhere mid-span of the lacing attachments to provide strength and stability to the chords on which they are disposed. 
         [0024]      FIG. 3  is a perspective view of a detail of the boom  106 .  FIG. 3  shows the attachment of chord  114  and perpendicular inter-chord lacings  116  and  120  as well as oblique inter-chord lacing  118   a.  Also shown is internal lacing  124   a.  Each of the lacing attachments may be positioned such that neither the lacing nor its associated weld joint  132  touches or overlaps another lacing/weld joint. This positioning facilitates inspection of weld joints and lacings. The positioning also facilitates repair or replacement of lacings or their weld joints because no other lacing must be cut or removed during the operation, in contrast to current, overlapping lacing implementations. 
         [0025]      FIG. 4A  is a perspective view of another detail of the boom  106 . Perpendicular inter-chord lacing  120  is shown with internal lacings  122 ,  124 , and  126 . In an embodiment, the inter-chord lacing  120  is a pipe, similar to other lacings. In another embodiment, the inter-chord lacing  120  may also be formed from a metal plate such that the lacing is open on one side, similar to the chords  110 ,  112 , and  114 . The open side of the lacing allows both sides of the weld joint to be visually inspected and the internal lacings  122 ,  124  and  126  to have flat, planar end cuts, as discussed in detail below. 
         [0026]      FIG. 4B  is a perspective view of an alternate embodiment of the boom detail of  FIG. 4A . In this embodiment, the inter-chord lacing  120 A is made from a rectangular pipe with the internal lacings  122 A,  124 A, and  126 A also being made of rectangular pipes. In an alternate embodiment the inter-chord lacing  120 A and the internal lacings  122 A,  124 A, and  126 A may be made from square tubing or tubing of another shape. In yet other embodiments, lacings of various shapes may be wed together. For example, an embodiment may use rectangular inter-chord lacings  120 A and round internal lacings  124 ,  126  so that the internal lacings  124 ,  126  also benefit from having planar end cuts, avoiding the coped end cuts required by round-on-round connections. 
         [0027]    In another embodiment, the inter-chord lacing  120 A may be formed from a metal plate and may have a U-shaped profile or an asymmetric profile with two sides perpendicular for mounting internal lacings  122 A,  124 A, and  126 A. For example, the inter-chord lacing  120 A may have a profile the same or similar to that of the chord  114  illustrated in  FIG. 7 . 
         [0028]      FIG. 5  is an end view of a cross-section of the boom  106 . In the illustrated embodiment, the boom has an isosceles triangle shape, with symmetric lacings  116  and a base lacing  120  longer than either side lacing  116 . In another embodiment, the boom  106  may have an equilateral triangular cross-section. In this latter case, each chord  110 ,  112 ,  114  would be symmetric, similar in shape to chord  110  shown in  FIG. 5 . 
         [0029]      FIG. 5  also illustrates supports  128  and  130 , being formed to contact the inside surface of their respective chords  110  and  114 . In an embodiment, the supports  128  and  130  are flat metal plates disposed perpendicular to a length of the chord and are welded to the inside surfaces of the chords. 
         [0030]      FIG. 6  is an end view of an exemplary top chord  110  of the boom  106 . The chord  110  may be formed from a sheet of metal, such as steel. The chord  110  may include a bottom mounting surface  140  and two side mounting surfaces  142  and  144 . The mounting surfaces  140 ,  142 ,  144  are planar and may be used to attach lacings, either inter-chord lacings or internal lacings. The mounting surfaces  140 ,  142 ,  144  form an open inverted frustum shape where the mounting surfaces  140 ,  142  and  144  may also be considered outside surfaces. Each mounting or outside surface  140 ,  142 ,  144  has a respective inside surface  141 ,  143 ,  145 . The junction of adjacent mounting surfaces, for example, the junction of adjacent mounting surfaces  140  and  142  form a reflex angle  146 . The junction of adjacent inside surfaces  141 ,  143  form an obtuse angle  148 . The support  128  is formed to contact in full or in part, each of the inside surfaces  141 ,  143 ,  145 . Note that a reflex angle is greater than 180 degrees and less than 360 degrees while an obtuse angle is greater than 90 degrees and less than 180 degrees. 
         [0031]      FIG. 7  is an end view of an exemplary side chord  114 . The chord  114  has outside, or mounting surfaces  150  and  152 . Each mounting surface  150  and  152  has a respective inside surface  151  and  153 . The adjacent mounting surfaces  150  and  152  form a reflex angle  154 . The inside surfaces  151  and  153  form an obtuse angle  156 . The chord  114  may include a third leg  157  with an inside surface  158 . The additional leg  157  helps increase the stability and load-bearing capability of the chord  114 . The support  130  is formed to contact in full or in part each of the inside surfaces  151 ,  153 , and  158 . 
         [0032]    For both the top chord  110  and the side chord  114 , the supports  128  and  130  are coupled to the inside surfaces of the chords. The supports  128  and  130  help prevent the chords  110  and  114  from deflecting due to lacing forces, that is, those forces occurring during both at rest due to gravity and also by movement of the boom when material is loaded and unloaded. The supports  128  and  130  also limit twist and buckling of the chord  110  and  114 . 
         [0033]      FIG. 8  depicts attachment relationships between chords  110 ,  114  and lacings  116 ,  120 , and  164  of an exemplary boom  106 . The mounting surface  142  of chord  110  defines a first plane. The mounting surface  150  of the chord  114  defines a second plane. The chords  110  and  114  are arranged so that the first and second plane are generally parallel. Therefore, a perpendicular inter-chord lacing  116  attached to the mounting surfaces  142  and  150  will be perpendicular to both chord mounting surfaces  142  and  150 . 
         [0034]    Similarly, an inter-chord lacing  120  will be perpendicular to both mounting surfaces  152  and  162  of the side chords  112  and  114 . A lacing  164  connecting mounting surfaces  144  and  160  will also be perpendicular to the plane defined by those mounting surfaces  144 ,  160 . The end of each of these lacings lies in a single plane and can be cut with a single cut of, for example, a circular saw, band saw, or cutoff saw to form a planar end cut. The complex coping cuts required for round lacing attachment to round chords of prior boom implementations are avoided. As can be seen in  FIGS. 3 and 4 , even oblique inter-chord lacings or the chord-side attachment end of an internal lacings will have ends that lie in a single plane, i.e., that can be made with a single cut-off cut. 
         [0035]    Further, the open frustum shape of the chords  110 ,  112 ,  114  allows visual inspection of both sides of weld joints that attached the lacings to the chords  110 ,  112 ,  114 . This improves the quality of an inspection because both sides of a chord can be easily viewed so that cracks and imperfections can be identified. 
         [0036]      FIG. 9  is an end view of an alternate embodiment of a boom  170  having four chords  172 ,  174 ,  176 , and  178 . The four-chord boom uses individual chords with a similar open frustum shape described above that allows inter-chord lacings  180 ,  182 ,  183 , and  186  to have planar end cuts and internal chords  188 ,  190  to have at least the chord-ends with planar end cuts. This four chord embodiment also preserves the open back of the chords of  FIGS. 6 and 7  so that compared to prior art round-chord booms inspections are easier and more effective and repairs can be more efficiently effected. The additional feature of offset lacing welds is also maintained in this embodiment. 
       INDUSTRIAL APPLICABILITY 
       [0037]      FIG. 10  is a flowchart  200  of a method of making a boom  106 . At a block  202 , a metal plate may be formed into a chord  110  with an inverted frustum shape having outside surfaces at a reflex angle and inside surfaces at an obtuse angle. The metal plate may be steel, aluminum, or another composition. 
         [0038]    At block  204 , additional chords  112 ,  114  may be formed from additional metal plates; the shape of the additional chords may be the same or different as the chord formed at block  202 . 
         [0039]    At block  206 , lacings may be formed with a planar end profile. That is, lacings made of round pipe may have ends that form a single plane, either perpendicular to a longitudinal axis of the pipe or oblique to the longitudinal axis. For example, the chord-end of any lacing may be cut with a band saw, a cutoff saw, or a circular saw. 
         [0040]    At block  208 , the chord  110  and the additional chords  112 ,  114  may be coupled with lacing so that one outside surface  142 ,  144  of a first chord  110  faces a respective outside surface  150 ,  160  of one other chord  112 ,  114 . Coupling the chord  110  and the additional chords  112 ,  114  with lacing may also include attaching each end of a lacing  116  to the outside surfaces  142 ,  150  of two facing chords  110 ,  114 . Coupling the chord  110  and the additional chords  112 ,  114  with lacing may also include attaching each end of the lacing so that no lacing, e.g., lacing  116 , is in contact with another lacing, e.g., lacing  118   a.  The lacings are typically attached with welds, but in the case where other materials or composites may be used for the chords, the chords and lacings may have different attachments, such as rivets, bolts, or epoxies. 
         [0041]    At block  210 , a support  128 ,  130  may be disposed between the inside surfaces of the chord. The support  128   130  may be a formed plate that is attached perpendicular to a length of a chord  110 ,  112 ,  114  and in contact with the inside surfaces  141 ,  143 ,  145  and  151 ,  153 ,  158  of respective chords  110 ,  114 . Chord  112  may be a mirror image of chord  114  and has similar inside surfaces that contact similar supports. The supports  128 ,  130  may be disposed opposite points where a lacing is attached or may be disposed mid-span between lacings. 
         [0042]    The use of formed chords rather than tubular pipe chords has the advantage of allowing both sides of a weld joint to be inspected and repaired. The separation of lacing attachment points allows a lacing and its welds to be individually inspected and, if needed, repaired without impacting other lacings. Dragline machine booms  106  are typically inspected every month. Since a boom  106  of a dragline machine  100  may be over 400 feet long and have hundreds, if not thousands, of lacings and welds, any improvement in the inspection and repair processes may have a considerable impact on machine up-time. However, the advantages of the chord and lacing techniques disclosed herein are not limited to dragline machines  100 . Any chord-based support structure may benefit from the formed chord and offset lacings discussed in this disclosure, including, but not limited to, portable cranes, overhead cranes, conveyor system supports, antenna towers, etc.

Summary:
A boom uses formed plates instead of a round pipes for the chords of the boom. Each formed plate provides a flat surface for attaching lacings so that complex coping cuts required for round pipe chords can be eliminated. The boom also displaces lacing attachment points so that overlapping welds in previous boom assemblies are also eliminated. The open back of the formed plate and non-overlapping lacing attachment points eliminate hidden welds and obscured mounting surfaces that make inspections and repairs of current boom assemblies difficult or impossible.