Abstract:
A method of mounting an attachment on an arm of a material handling machine including the steps of:
       (a) providing an arm including a first plate, a second plate and a pair of side walls welded to each of the first plate and the second plate, the arm having a connector for pivotable mounting of the attachment at a first end of the arm and a connector for pivotable mounting to a further component of the material handling machine at a second end of the arm opposite to the first end; wherein the second plate has two opposite edges and a first of the pair of side walls is welded inward of one edge and a second of the pair of side walls is welded inward of the other edge to form two flanges, each of the two flanges extending on opposite sides of the second plate and each of the two flanges having at least one hole at each of its ends;   (b) providing a bracket including a mounting plate having a pair of lugs for supporting an actuator for the attachment; the pair of lugs being positioned in a central portion of the mounting plate; and the mounting plate having at least one hole adjacent to each of its corners;   (c) aligning the holes of the mounting plate with the holes on each of the pair of flanges;   (d) securing the bracket on the arm by securing the mounting plate to each of the pair of the flanges by passing a fastener through each hole of the mounting plate and the corresponding hole on each of the pair of flanges;   (e) mounting the actuator for the attachment on the pair of lugs;   (f) mounting the attachment on the connector at the first end of the arm; and   (g) connecting the actuator to the attachment.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of mounting an attachment on an arm of a material handling machine. The present invention also relates to an arm for a material handling machine. 
       BACKGROUND OF THE INVENTION 
       [0002]    Known material handling machines, such as excavators, have a material handling arm assembly. The arm assembly may have a first arm, known as a boom, pivotally mounted about a generally horizontal axis relative to a chassis of the machine. A second arm, known as a dipper, may be attached to an end of the boom remote from the chassis and may be pivotable about a generally horizontal axis. A material handling implement, such as a bucket, may be pivotally mounted on an end of the dipper. The boom may be raised and lowered by operation of a first hydraulic ram. The dipper may be movable relative to the boom by operation of a second hydraulic ram. The bucket may be movable relative to the dipper by operation of a third hydraulic ram. 
         [0003]    It is known to retrofit actuated attachments, for example clamps, known as thumbs, to material handling machines. Such clamps or thumbs may be pivotally mounted adjacent to the bucket on an end of the dipper. The clamp or thumb may be used to grip against the bucket to pick up objects, for example rocks or tree trunks. The clamp or thumb may be movable to lie against the dipper when not in use. The clamp or thumb may be movable relative to the bucket and the dipper by operation of a fourth hydraulic ram. The fourth hydraulic ram may be mounted on the dipper remote from the bucket and the clamp or thumb. The fourth hydraulic ram may be mounted on the dipper via a mount or bracket that is welded to the dipper. In particular the mounted bracket may be welded to a face of the dipper arm, which face may be the furthest point from a neutral axis of the dipper arm. The weld used to weld the mounted brackets onto the dipper arm may therefore be the first weld on that face of the dipper arm. 
         [0004]    The fatigue life of dipper arms to which mounted brackets are welded is reduced by a combination of the stress concentration effect of welding and the size and weight of the mount or bracket on the dipper. The highest and lowest points of dippers in such modified material handling machines experience increased stresses, even when the clamp or thumb is not in use, i.e. when the bucket is being used to pick up and move material. 
         [0005]    The impact of these effects can be reduced by providing reinforced or heavier dippers, however this increases the amount of material required to construct the material handling machine and results in heavier material handling machines. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the present invention there is provided a method of mounting an attachment on an arm of a material handling machine including the steps of:
       (a) providing an arm including a first plate, a second plate and a pair of side walls welded to each of the first plate and the second plate, the arm having a connector for pivotable mounting of the attachment at a first end of the arm and a connector for pivotable mounting to a further component of the material handling machine at a second end of the arm opposite to the first end; and wherein the second plate has two opposite edges and a first of the pair of side walls is welded inward of one edge and a second of the pair of side walls is welded inward of the other edge to form two flanges, each of the two flanges extending on opposite sides of the second plate and each of the two flanges having at least one hole at each of its ends;   (b) providing a bracket including a mounting plate having a pair of lugs for supporting an actuator for the attachment; the pair of lugs being positioned in a central portion of the mounting plate; and the mounting plate having at least one hole adjacent to each of its corners;   (c) aligning the holes of the mounting plate with the holes on each of the pair of flanges;   (d) securing the bracket on the arm by securing the mounting plate to each of the pair of the flanges by passing a fastener through each hole of the mounting plate and the corresponding hole on each of the pair of flanges;   (e) mounting the actuator for the attachment on the pair of lugs;   (f) mounting the attachment on the connector at the first end of the arm; and   (g) connecting the actuator to the attachment.       
 
         [0014]    Securing the bracket for mounting the actuator for the attachment on the arm to flanges on the arm using fasteners that are passed through holes in the bracket and corresponding holes in the flanges eliminates the stress concentration effect of welding and ensures any stresses caused by the weight of the bracket and the mounted actuator and thumb are distributed across the flanges, thereby removing the need for a reinforced dipper arm. 
         [0015]    The first plate may have two opposite edges. One of the pair of side walls may be welded inward of the first edge of the first plate and the other of the pair of side walls may be welded inward of the opposite edge of the first plate. 
         [0016]    The second plate may have a first face that faces the first plate and the pair of side walls may be welded to the first face. 
         [0017]    Each of the two flanges may have a length that is approximately one third to one sixth of the length of the arm, preferably one quarter to one fifth of the length of the arm. 
         [0018]    Each of the two flanges may have a length that is in the range 0.05 m to 2.00 m, preferably 0.15 m to 0.50 m. Each of the two flanges may extend in a direction that is parallel to the other of the two flanges. 
         [0019]    The ratio of the width of each of the flanges to the length of each of the flanges may be 1:3 to 1:5. 
         [0020]    Each of the two flanges may have an outer edge and the outer edges of the flanges may be substantially parallel to each other. 
         [0021]    The length of the flanges is selected to advantageously distribute the mounted bracket, actuator and thumb without significantly increasing the weight of the arm. 
         [0022]    Each of the flanges may be positioned toward the connector for pivotable mounting to a further component of the material handling machine. 
         [0023]    Each flange may have two lugs, the two lugs being spaced apart and defining each of the ends of the flange. The lugs may comprise the at least one hole at each end of the flange. 
         [0024]    A bucket may be pivotably mounted at the first end of the arm. The bucket may be movable in a crowd direction or a dump direction relative to the arm and the open face of the bucket may generally face the bracket. 
         [0025]    Each of the flanges may have a width that is in the range 20 mm to 70 mm, preferably 25 mm to 35 mm. 
         [0026]    Each of the two flanges may have two holes at each of its ends and each corner of the mounting plate may have two holes. 
         [0027]    Each of the two holes in each of the two flanges may be arranged along the length of the respective flange and each of the two holes in each of the corners of the mounting plate are arranged along the length of the mounting plate. 
         [0028]    The distance between the at least one hole at each end of each of the flanges and a weld line between the second plate and the side wall to which the second plate is welded may be at least 5 mm, preferably at least 10 mm. 
         [0029]    The mounting plate may have a thickness in the range 5 mm to 30 mm. 
         [0030]    The second plate may have a thickness and the ratio of the mounting plate thickness to the second plate thickness may be approximately 4:1 to 2:1. 
         [0031]    Each of the pair of lugs may have a foot that extends in a direction parallel to the length of the mounting plate. 
         [0032]    Each of the pair of lugs may have a generally annular body having an aperture. 
         [0033]    The aperture of each of the pair of lugs may be offset relative to the center of the foot of the respective lug. 
         [0034]    The fasteners that are passed through each hole of the mounting plate and the corresponding hole on each of the pair of flanges may be one or more of a threaded fastener or a bolt or a rivet. 
         [0035]    The attachment may be a thumb. 
         [0036]    The arm may have a length. The connector for pivotable mounting of the attachment at a first end of the arm may have a first pivot axis. The connector for pivotable mounting to a further component of the material handling machine at a second end of the arm may have a second pivot axis. The distance between the first pivot axis and the second pivot axis may be substantially equal to the length of the arm. 
         [0037]    According to a second aspect of the present invention there is provided an arm for a material handling machine including: a first plate; a second plate; a pair of side walls welded to each of the first plate and the second plate; the second plate including two flanges, each of the two flanges extending on opposite sides of the second plate and having at least one hole at each of its ends; and wherein each of the flanges has a length that is longitudinal with respect to the arm and a width that is transverse with respect to the arm and the length of each flange is between ⅓ and ⅙ of the length of the arm, wherein the second plate has two opposite edges and a first of the pair of side walls is welded inward of the first edge of the second plate and a second of the pair of side walls is welded inward of the opposite edge of the second plate to form the two flanges on the second plate. 
         [0038]    The length of each flange may be between ¼ and ⅕ of the length of the arm. 
         [0039]    The first plate may have two opposite edges and one of the pair of side walls may be welded inward of the first edge of the first plate and/or the other of the pair of side walls may be welded inward of the opposite edge of the first plate. 
         [0040]    The second plate may have a first face that faces the first plate and the pair of side walls may be welded to the first face. 
         [0041]    Each of the two flanges may have two holes at each of its ends. 
         [0042]    The two holes at each end of each of the two flanges may be arranged longitudinally with respect to the respective flange. 
         [0043]    The distance between the at least one hole at each end of each of the flanges may be up to approximately 1.95 m, preferably in the range of approximately 0.10 m to 0.45 m. 
         [0044]    The at least one hole at each end of each of the flanges may be separated by a distance of approximately 20 mm to 70 mm, preferably approximately 25 mm to 35 mm. 
         [0045]    The distance between the at least one hole at each end of the flange and a weld line between the second plate and the side wall to which the second plate is welded may be at least 5 mm, preferably at least 10 mm. 
         [0046]    The arm may have a first end for pivotable mounting of an implement and a second end for pivotable mounting to a further component of the material handling machine and/or each of the flanges may be positioned toward the second end of the arm. 
         [0047]    A bucket may be pivotably mounted at the first end of the arm. The bucket may be movable in a crowd direction or a dump direction relative to the arm and the open face of the bucket may generally face the two flanges. 
         [0048]    Each of the two flanges may have a width in the range 20 mm to 70 mm, preferably 25 mm to 35 mm. 
         [0049]    According to a third aspect of the present invention there is provided a material handling machine including a chassis having a ground engaging propulsion structure;
       a loading arm assembly pivotably mounted via a substantially horizontal axis to the machine; the loading arm assembly including an arm according to the second aspect of the present invention.       
 
         [0051]    The material handling machine may further comprise a body having a vertical axis, wherein the arm is mounted on the body. 
         [0052]    The ground engaging propulsion structure may include a pair of wheels or a continuous loop track at either side of the body. 
         [0053]    The arm assembly may include a boom and the arm may be pivotably mounted with respect to the boom. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0054]    The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0055]      FIG. 1  is a schematic side view of a material handling machine for use in a method according to the present invention; 
           [0056]      FIG. 2  is a schematic view of part of the material handling machine of  FIG. 1 ; 
           [0057]      FIG. 3  is a perspective view of the dipper of  FIG. 1 ; 
           [0058]      FIG. 4  is a perspective view of a ram bracket for mounting an actuated attachment on a dipper; 
           [0059]      FIG. 5  is a perspective view of the ram bracket of  FIG. 4  mounted on a dipper; and 
           [0060]      FIG. 6  is a side view of a dipper to which a thumb has been mounted in accordance with the method of the present invention; and 
           [0061]      FIG. 7  is a schematic view of part of an alternative material handling machine for use in a method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0062]    With reference to  FIGS. 1 and 2 , there is shown a material handling machine  10 , which in this example is an excavator, including a chassis  12  and an operator cab  14 . The operator cab  14  is mounted on the chassis  12 . Ground engaging transport means in the form of a pair of tracks  16  are provided to move the machine  10  over the ground  2 . 
         [0063]    Attached to the chassis  12  is an arm assembly  18  (also known as an implement support system). The arm assembly  18  includes a first arm in the form of a boom  20 , a second arm in the form of a dipper  22  and a ground engaging implement in the form of a bucket  24 . The bucket  24  has bucket teeth  25 . The boom  20  is pivotally mounted by pivot  26  to link  12 A at a first end  20 A of the boom  20 . Link  12 A is pivotally mounted at a generally vertical axis relative to the chassis  12 . Pivot  26  is orientated horizontally. The dipper  22  is pivotally mounted via pivot  28  to a second end  20 B of the boom  20 . Pivot  28  is orientated horizontally and has an axis A. The bucket  24  is pivotally mounted via pivot  30  to an end  22 B of dipper  22  remote from end  22 A of dipper  22 . Pivot  30  is orientated horizontally and has an axis B. Axis A of pivot  28  and axis B of pivot  30  are separated by a distance C, as shown in  FIG. 3 . 
         [0064]    With reference to  FIG. 3 , the dipper  22  includes a box-section comprising two side walls (only one of which,  62 , is shown in  FIG. 3 ), a first plate  64  and a second plate  66 . As shown, the dipper  22  tapers towards the end  22 B, but the dipper  22  could be of constant width. The first plate  64  has two opposing surfaces or faces (only one of which,  64 B, is shown in  FIG. 3 ). As shown in  FIG. 3 , surface or face  64 B of the first plate  64  faces towards the second plate  66 . 
         [0065]    The first plate  64  includes a flange  68 , which is positioned toward end  22 A of the dipper  22  and which extends outwards from the width of the first plate  64  (i.e. the flange  68  is integral with the first plate  64 ). The flange  68  and the first plate  64  are made from a single sheet of metal (i.e. the flange  68  and the first plate  64  are unitary components). 
         [0066]    The flange  68  has two opposing surfaces (only one of which,  68 A, is shown in  FIG. 3 ). The surface  68 A of the flange  68  is substantially flush with the surface or face  64 B of the first plate  64 . The flange  68  includes a pair of holes  70 A,  70 B which extend through the two opposing surfaces in the flange  68 . The first plate  64  may include a second flange (not shown) on the side opposite to flange  68 . 
         [0067]    The second plate  66  has two opposing surfaces or faces (only one of which,  66 B, is shown in  FIG. 3 ). As shown in  FIG. 3 , surface or face  66 B of the second plate  66  faces away from the first plate  64 . The second plate  66  has a first end  134  adjacent to pivot  28  and a second end  136  adjacent to pivot  30 . The second plate  66  has a length D that corresponds to the distance between the first end  134  and the second end  136  of the second plate  66 . The length D of the second plate  66  is substantially the same as the distance C between pivot axis A and pivot axis B. 
         [0068]    The second plate  66  has a first outer edge  66 A that extends between the first end  134  and the second end  136  of the second plate  66  and a second outer edge  66 C that extends between the first end  134  and the second end  136  of the second plate  66 . 
         [0069]    The first outer edge  66 A is opposite to the second outer edge  66 C. The first outer edge  66 A and the second outer edge  66 C are separated by a distance E proximal to the first end  134  of the second plate  66 . The distance E corresponds to the width of the second plate  66  adjacent to the first end  134  of the second plate  66 . 
         [0070]    The first outer edge  66 A and the second outer edge  66 C are separated by a distance F proximal to the second end  136  of the second plate  66 . The distance F corresponds to the width of the second plate  66  adjacent to the second end  136  of the second plate  66 . 
         [0071]    As shown in  FIG. 3 , the distance E is substantially the same as the distance F, i.e. the width of the second plate  66  at the first end  134  is substantially the same as the width of the second plate  66  at the second end  136  of the second plate  66 . It will be understood that the distance E may be greater than the distance F i.e. the width E of the second plate  66  at the first end  134  may be greater than the width F of the second plate  66  at the second end  136 , for example if the second end  136  of the second plate  66  tapers from the first end  134  of the second plate  66 . 
         [0072]    A first portion  73 A of the first outer edge  66 A of the second plate  66  that is positioned toward the first end  134  of the second plate  66  extends or curves outward from the width E of the second plate  66  and a second portion  73 B of the first outer edge  66 A extends or curves inward toward the second end  136  of the second plate  66  to form a first flange  72  that is integral with the second plate  66  and that extends between the first end  134  and the second end  136  of the second plate  66 . 
         [0073]    The first flange  72  has a first end  72 B positioned toward the first end  134  of the second plate  66  and a second end  72 C positioned toward the second end  136  of the second plate  66 . The first end  72 B and the second end  72 C of the first flange  72  are separated by a distance G. The distance G corresponds to the length of the first flange  72 , which is approximately one quarter to one fifth of the length D of the second plate  66 . The first flange  72  has an outer edge  72 D. 
         [0074]    In a similar way, a first portion  75 A of the second outer edge  66 C of the second plate  66  that is positioned toward the first end  134  of the second plate  66  extends or curves outward from the width E of the second plate  66  and a second portion  75 B of the second outer edge  66 C extends or curves inward toward the second end  136  of the second plate  66  to form a second flange  74  that is integral with the second plate  66  and that extends between the first end  134  and the second end  136  of the second plate  66 . 
         [0075]    The second flange  74  has a first end  74 B positioned toward the first end  134  of the second plate  66  and a second end  74 C positioned toward the second end  136  of the second plate  66 . The first end  74 B and the second end  74 C of the second flange  74  are separated by a distance I. The distance I corresponds to the length of the second flange  74 , which is approximately one quarter to one fifth of the length D of the second plate  66 . The length I of the second flange  74  is substantially the same as the length G of the first flange  72 . The second flange  74  has an outer edge  74 D. 
         [0076]    The first flange  72  is positioned opposite the second flange  74  on the second plate  66  such that the width K of the portion of the second plate  66  having the first and second flanges  72 ,  74  is equal to the sum of the widths E, H and J. The outer edge  72 D of the first flange  72  is substantially parallel to the outer edge  74 D of the second flange. 
         [0077]    The second plate  66  is made from a single sheet of metal (i.e. the first and second flanges  72 ,  74  and the second plate  66  are unitary components). 
         [0078]    The first flange  72  has two opposing surfaces (only one of which,  72 A is shown in  FIG. 3 ) and includes a first pair of holes  76 A,  76 B adjacent to its first end  72 B and a second pair of holes  78 A,  78 B adjacent to its second end  72 C. Each of the holes  76 A,  76 B,  78 A,  78 B extends through the two opposing surfaces of the first flange  72 . Surface  72 A of the first flange  72  is substantially flush with the surface  66 B of the second plate  66 . 
         [0079]    Similarly, the second flange  74  has two opposing surfaces (only one of which,  74 A, is shown in  FIG. 3 ) and includes a first pair of holes  80 A,  80 B adjacent to its first end  74 B and a second pair of holes  82 A,  82 B adjacent to its second end  74 C. Each of the holes  80 A,  80 B,  82 A,  82 B extends through the two opposing surfaces of the second flange  74 . Surface  74 A of the second flange  74  is substantially flush with the surface  66 B of the second plate  66 . 
         [0080]    To form the box-section, the side wall  62  is welded inward of an edge  64 A of the first plate  64  on the surface or face  64 B such that a lip  84  is formed adjacent to the edge  64 A of the first plate  64 . The side wall  62  is similarly welded inward of the first outer edge  66 A of the second plate  66  on the surface opposite to surface  66 B (i.e. the surface that faces the first plate  64 ) such that a first lip  86 A is formed between the first end  134  of the second plate  66  and the first end  72 B of the first flange  72  and a second lip  86 B is formed between the second end  72 C of the first flange  72  and the second end  136  of the second plate  66 . The second side wall (not shown) is welded in a similar way inward of an edge (not shown) of the first plate  64  (on the surface or face  64 B) and inward of the second outer edge  66 C of the second plate  66  (on the surface opposite to surface  66 B) such that a first lip  87 A is formed between the first end  134  of the second plate  66  and the first end  74 B of the second flange  74  and a second lip  87 B is formed between the second end  74 C of the second flange  74  and the second end  136  of the second plate  66 . 
         [0081]    The first lip  86 A has an outer edge  86 C and an inner edge (not shown) that is located at the weld line between the side wall  62  and the second plate  66  toward the first end  134  of the second plate  66 . The width L of the first lip  86 A is defined by the distance between the outer edge  86 C and the inner edge (not shown) of the first lip  86 A. 
         [0082]    The second lip  86 B has an outer edge  86 D and an inner edge (not shown) that is located at the weld line between the side wall  62  and the second plate  66  toward the second end  136  of the second plate  66 . The width M of the second lip  86 B is defined by the distance between the outer edge  86 D and the inner edge (not shown) of the second lip  86 B. The width M of the second lip  86 B is substantially equal to the width L of the first lip  86 A. 
         [0083]    The width H of the first flange  72  is defined by the distance the outer edge  72 D of the first flange  72  extends outward from the second plate  66  relative to the inner edge (not shown) of the first lip  86 A or the second lip  86 B. The width H of the first flange  72  is greater than the width L of the first lip  86 A or the width M of the second lip  86 B. 
         [0084]    The third lip  87 A has an outer edge  87 C and an inner edge (not shown) that is located at the weld line between the side wall (not shown) and the second plate  66  toward the first end  134  of the second plate  66 . The width N of the third lip  87 A is defined by the distance between the outer edge  87 C and the inner edge (not shown) of the first lip  87 A. 
         [0085]    The fourth lip  87 B has an outer edge  87 D and an inner edge (not shown) that is located at the weld line between the side wall (not shown) and the second plate  66  toward the second end  136  of the second plate  66 . The width P of the fourth lip  87 B is defined by the distance between the outer edge  87 D and the inner edge (not shown) of the second lip  87 B. The width P of the fourth lip  87 B is substantially equal to the width N of the third lip  87 A. 
         [0086]    The width J of the second flange  74  is defined by the distance the outer edge  74 D of the second flange  74  extends outward from the second plate  66  relative to the inner edge (not shown) of the third lip  87 A or the fourth lip  87 B. The width J of the second flange  74  is greater than the width N of the third lip  87 A or the width P of the fourth lip  81 B. 
         [0087]    The side walls  62  are thus welded inward of the edges of the first plate  64  and second plate  66  so that the side walls  62  are inset from the edges of the first plate  64  and the second plate  66 . The lips  84 ,  86 A,  86 B,  87 A,  87 B are wide or thick enough to allow for welding of the side plates to the first plate  64  and/or the second plate  66 . The thickness or width of the lips  84 ,  86 A,  86 B,  87 A,  87 B is less than the width H of the first flange  72  and the width J of the second flange  74 , both of which are thick or wide enough to accommodate bolts in addition to weld lines. The lips  84 ,  86 A,  86 B,  87 A,  87 B, the first flange  72  and the second flange  74  are integral with the second plate  66 . The weld lines extend along inner surfaces of the first plate  64  and the second plate  66 , which experience compression forces during operation of the dipper  22  (when the outer surfaces of the first plate  64  and the second plate  66  experience tension forces). 
         [0088]    With reference now to  FIG. 4 , there is shown a bracket  108  for mounting an actuated attachment on the dipper  22 . 
         [0089]    The bracket  108  includes a mounting plate  110  and a pair of lugs  112 A,  112 B. 
         [0090]    The mounting plate  110  is rectangular in shape has two opposing surfaces  111 A,  111 B and has side edges  122 A,  122 B and ends  124 A,  124 B. At the corner of edge  122 A and end  124 A there is a first pair of holes  114 A,  114 B. At the corner of edge  122 A and end  124 B there is a second pair of holes  116 A,  116 B (shown in  FIG. 5 ). At the corner of edge  122 B and end  124 A there is a third pair of holes  118 A,  118 B. At the corner of edge  122 B and end  124 B there is a fourth pair of holes  120 A,  120 B. Each of the first, second, third and fourth pair of holes  114 A,  114 B,  116 A,  116 B,  118 A,  118 B,  120 A,  120 B extends through the two opposing surfaces  111 A,  111 B. The width of the mounting plate  110  from edge  122 A to edge  122 B corresponds to the combined width of the second plate  66  and the flanges  72  and  74 . The length of the mounting plate  110  from end  124 A to  124 B corresponds to the length of flanges  72  and  74 . 
         [0091]    The lug  112 A has a generally circular body  126 A and an elongate foot  127 A. The generally circular body  126 A is offset relative to the center of the elongate foot  127 A and includes an aperture  128 A. The lug  112 B is the same shape as lug  112 A and has generally circular body  126 B and an elongate foot  127 B. The generally circular body  126 B is offset relative to the center of the elongate foot  127 B and includes an aperture  128 B. 
         [0092]    Lug  112 A is welded on the mounting plate  110  such that the elongate foot  127 A is positioned inward of edge  122 A, the length of the elongate foot  127 A extends in a direction parallel to the edge  122 A and the generally circular body  126 A extends away from surface  111 A. Lug  112 B is welded on the plate  100  such that the elongate foot  127 B is positioned inward of edge  122 B, the length of the elongate foot  127 B extends in a direction parallel to the edge  122 B and the generally circular body  126 B extends away from surface  111 A. 
         [0093]    A method of mounting a thumb  100  on the dipper  22  will now be described with particular reference to  FIGS. 5 and 6 . 
         [0094]    The holes  114 A,  114 B and  116 A,  116 B of the mounting plate  110  are aligned with holes  76 A,  76 B and  78 A,  78 B, respectively on flange  72 . In this configuration, surface  111  B of the mounting plate  110  is adjacent to surface  72 A of flange  72 . Holes  118 A,  118 B and  120 A,  120 B of the mounting plate  110  are aligned with holes  80 A,  80 B and  82 A,  82 B, respectively on flange  74 . In this configuration, surface  111 B of the mounting plate  110  is adjacent to surface  74 A of flange  74 . A fastener  88  is passed through each of the holes in order to bring surface  111 B of the mounting plate  110  into engagement with surfaces  72 A,  74 A of the flanges  72 ,  74  and secure the mounting plate  110  to the flanges  72 ,  74 . The fourth hydraulic ram  106  is mounted by passing a pin  90  through the apertures  128 A,  128 B on the lugs  112 A,  112 B of the bracket  108  and a connector (not shown) on the fourth hydraulic ram  106 . The thumb  100  is mounted on the dipper  22  by pivot  130 . The second end  106 B of the fourth hydraulic ram  106  opposite to the end  106 A that is mounted on the lugs  112 A,  112 B is then mounted on the connector  104  of the thumb  100 . 
         [0095]    Referring again to  FIGS. 1 and 2 , a first hydraulic actuator in the form of a first hydraulic ram  32  has a first end  32 A pivotally attached to the chassis  12  and a second end  32 B pivotally attached to the boom  20  part way between the first  20 A and second  20 B ends of the boom  20 . A second hydraulic actuator in the form of a second hydraulic ram  34  has a first end  34 A pivotally attached to the boom  20  part way between the first  20 A and second  20 B ends of the boom  20  and a second end  34 B pivotally attached to the dipper  22  proximate the first end  22 A of the dipper  22 . A third hydraulic actuator in the form of a third hydraulic ram  36  has a first end  36 A pivotally attached to the dipper  22  proximate the first end  22 A of the dipper  22  and a second end  36 B pivotally attached to a linkage mechanism  38  proximate the second end  22 B of the dipper  22 . The linkage mechanism  38  per se is known and simply converts extension and retraction movement of the third hydraulic ram  36  into rotary movement of the bucket  24  about pivot  30 . 
         [0096]    Extension of the first hydraulic ram  32  causes the boom  20  to rise, and contraction of the first hydraulic ram  32  causes lowering of the boom  20 . Extension of the second ram  34  causes the dipper  22  to pivot in a clockwise direction (when viewing  FIG. 1 ) about pivot  28 , i.e. the boom  20  is caused to move in a “dipper in” direction, and retraction of the second hydraulic ram  34  causes the dipper  22  to move in an anti-clockwise direction (when viewing  FIG. 1 ) about pivot  28 , i.e. the boom  20  is caused to move in a “dipper out” direction. Extension of the third hydraulic ram  36  causes the bucket  24  to move in a clockwise direction about pivot  30 , i.e. in a “crowd” direction, and retraction of the third hydraulic ram  36  causes the bucket to move in an anti-clockwise direction about pivot  30 , i.e. in a “dump” direction. 
         [0097]    The first  32 , second  34  and third  36  hydraulic rams are all double acting hydraulic rams. Double acting hydraulic rams are known per se. They include a piston within a cylinder. The piston is attached to a rod which extends beyond the end of the cylinder. The end of the rod remote from the piston defines one end of the hydraulic ram. The end of the cylinder remote from the rod defines an opposite end of the hydraulic ram. A “head side chamber” is defined between the piston and the end of the cylinder remote from the head. A “rod side chamber” is defined between the piston and the end of the cylinder proximate the end of the rod. Pressurization of the head side pressure chamber extends the ram and pressurization of the rod side chamber causes the ram to retract. 
         [0098]    The machine  10  includes a system for operating the first  32 , second  34  and third  36  hydraulic rams, as described below and with reference to  FIG. 2 . 
         [0099]    A hydraulic pump  40  is driven by a prime mover  41 . Prime mover  41  may be an internal combustion engine, though other prime movers are suitable. A boom spool valve  44  can be operated by an operator manipulating boom control  46 . In this case boom control  46  is a joystick. A dipper spool valve  48  can be controlled via a dipper control  50 . In this case dipper control  50  is a joystick. An implement spool valve  54  can be operated by an operator manipulating implement control  56 . In this case implement control  56  is a joystick. Joysticks  46 ,  50  and  54  may be separate joysticks (as shown in  FIG. 2 ). Alternatively, two of the boom control  46 , dipper control  50  and implement control  56  may be combined in a single joystick. Alternatively, all three of the boom control  46 , dipper control  50  and implement control  56  may be combined in a single joystick. Controls other than joysticks may be used to control one or more of the boom spool, dipper spool and implement spool. 
         [0100]    Operation of a material handling machine is as follows: 
         [0101]    The prime mover  41  drives the hydraulic pump  40  which takes hydraulic fluid from tank T and pressurizes hydraulic line L 1 . As shown in  FIG. 2 , the dipper spool valve  48  is closed, the implement spool valve  54  is closed, the boom spool valve  44  is closed and hence pressurized fluid in line L 1  will pass through the relief valve  51  back to tank T. 
         [0102]    If it is desired to raise the boom  20 , the boom control  46  is operated such that the boom spool  44 A of the boom spool valve  44  is moved so as to connect hydraulic line L 1  and hydraulic line L 2 . This causes hydraulic fluid to pass into the head side pressure chamber of the first hydraulic ram  32  thereby extending the first hydraulic ram  32  and raising the boom  20 . Hydraulic fluid from the rod side chamber passes into hydraulic line L 3  and back to tank T via the boom spool valve  44 . In order to lower the boom  20 , the boom control  46  is operated to move the boom spool  44 A in the opposite direction thereby connecting hydraulic line L 1  with hydraulic line L 3  and hydraulic line L 2  with tank T. 
         [0103]    In order to move the dipper  22  in a “dipper in” direction the dipper control  50  is operated such that the dipper spool  48 A of the dipper spool valve  48  connects hydraulic line L 1  with hydraulic line L 4 . Hydraulic line L 4  is connected to the head side of the second hydraulic ram  34  which causes the ram to extend thereby pivoting the dipper arm  22  in a clockwise direction about pivot  28 . Hydraulic fluid in the rod side of second hydraulic ram  34  passes into hydraulic line L 5  and then on through the dipper spool valve  48  to tank T. In order to move the dipper in a “dipper out” direction, the dipper control  50  is operated such that the dipper spool  48 A connects hydraulic line L 1  with hydraulic line L 5  and connects hydraulic line L 4  with tank T. This results in retraction of the second hydraulic ram  34  thereby causing the dipper  22  to move in an anti-clockwise direction above pivot  28 . 
         [0104]    In order to move the bucket  24  in a “crowd” direction, the implement control  56  is operated such that the implement spool  54 A of the implement spool valve  54  connects hydraulic line L 1  with hydraulic line L 6 . Hydraulic line L 6  is connected to the head side of the third hydraulic ram  36  which causes the ram to extend thereby pivoting the bucket  24  in a clockwise direction about pivot  30 . Hydraulic fluid in the rod side of third hydraulic ram  36  passes into hydraulic line L 7  and then on through the implement spool valve  54  to tank T. In order to move the bucket  24  in a “dump” direction the implement control  56  is operated such that the implement spool  54 A connects hydraulic line L 1  with hydraulic line L 7  and connects hydraulic line L 6  to the tank T. This results in retraction of the third hydraulic ram  36  thereby causing the bucket  24  to move in an anti-clockwise direction about pivot  30 . 
         [0105]    When digging a trench or the like a typical sequence of movements of the arm assembly  18  is as follows: 
         [0106]    Firstly, the boom  20  is lowered and the dipper  22  is moved in a “dipper out” direction thereby moving the bucket teeth  25  of the bucket  24  away from the chassis  12 . The boom  20  is then further lowered such that the bucket teeth  25  engage the ground  2 . The bucket  24  is then crowded slightly so as to start to move the bucket teeth  25  through the ground  2 . The dipper control  50 , boom control  46  and implement control  56  are then simultaneously operated to progressively move the dipper  22  in the “dipper in” direction, to move the boom  20  in a “boom raised” direction and to move the bucket  24  in a “crowd” direction such that the bucket teeth  25  move generally towards the chassis  12 . As will be appreciated, skill is involved in simultaneously manipulating the dipper control  50 , the boom control  46  and the implement control  56  to efficiently fill the bucket  24  with material. Once the bucket  24  is full, the boom  20  is raised, the arm assembly  18  is swung laterally relative to the machine  10  and the material is then dumped by moving the bucket  24  to the “dump” position. The sequence is then repeated. 
         [0107]    Referring now to  FIG. 6 , a thumb  100  and a bucket  24  are pivotally mounted via an extended pivot  130  to the second end  22 B of dipper  22 . Pivot  130  is orientated horizontally. 
         [0108]    The thumb  100  includes teeth  102  at an end  100 B opposite to the end  100 A at which it is pivotally mounted to the second end  22 B of dipper  22 . The thumb  100  also includes a connector  104  positioned on a side of the thumb  100  opposite to the teeth  102 . 
         [0109]    A fourth hydraulic actuator in the form of a fourth hydraulic ram  106  has a first end  106 A attached to a bracket  108  and a second end  106 B at which the fourth hydraulic ram  106  is connected to the connector  104  on the thumb  100 . 
         [0110]    Extension of the fourth hydraulic ram  106  causes the thumb  100  to move in an anti-clockwise direction about pivot  130 , i.e. towards the bucket  24 , and retraction of the fourth hydraulic ram  106  causes the thumb  100  to move in a clockwise direction about pivot  130 , i.e. away from the bucket  24 . 
         [0111]    The fourth hydraulic ram  106  is a double acting hydraulic rams and is operated in the same way as described for the first, second and third hydraulic rams. 
         [0112]    Operation of the material handling machine with the thumb is as follows: 
         [0113]    A thumb spool valve (not shown) can be operated by an operator manipulating thumb control (not shown), for example a joystick in order to control movement of the thumb  100 . 
         [0114]    In order to move the thumb  100  towards the bucket  24 , the thumb control (not shown) is operated such that the thumb spool of the thumb spool valve (not shown) connect a hydraulic line L 1  with a first hydraulic line (not shown) that is connected to the head side of the fourth hydraulic ram  106 , which causes the ram  106  to extend thereby pivoting the thumb  100  in an anti-clockwise direction about pivot  130 . Hydraulic fluid in the rod side of the fourth hydraulic ram  106  passes into a further hydraulic line (not shown) and then on through the thumb spool (not shown) valve (not shown) to tank T. In order to move the thumb  100  away from the bucket  24 , the thumb control (not shown) is operated such that the thumb spool connects hydraulic line L 1  with the further hydraulic line (not shown) and connects the first hydraulic line to the tank T. This results in retraction of the fourth hydraulic ram  106  thereby causing the thumb  100  to move in a clockwise direction about pivot  130 . 
         [0115]    When picking up a rock or tree trunk or the like, a typical sequence of movements of the arm assembly  18  is as follows: 
         [0116]    Firstly, the boom  20  is lowered and the dipper  22  is moved in a “dipper out” direction thereby moving the bucket teeth  25  of the bucket away from the chassis  12 . The boom  20  is then further lowered such that the bucket teeth  25  are positioned adjacent to the item to be picked up. The bucket  24  is then crowded slightly so as to start to move the bucket teeth  25  towards the rock or tree trunk. The thumb control is then operated to move the thumb  100  in towards the bucket  24  in order to grip the rock or tree trunk between the thumb  100  and the bucket teeth  25 . Once the rock or tree trunk are gripped between the bucket  24  and the thumb  100 , the boom  20  is raised, the arm assembly  18  is swung laterally relative to the machine  10  and the rock or tree trunk is then deposited in the required location by moving the thumb  100  away from the bucket  24 . The sequence is then repeated as necessary to collect and move multiple rocks or tree trunks. 
         [0117]    With reference to  FIG. 7  there is shown a material handling machine  210  including a chassis  212  and an operator cab  214 . Ground engaging transport means in the form of a pair of wheels of each side of the machine are provided to move the machine  210  over the ground  2 . Attached to the chassis  212  is an arm assembly  218  which includes a first arm in the form of a boom  220 , a second arm in the form of a dipper  222  and a ground engaging implement in the form of a bucket  224 . Machine  210  also includes a front loader arm  290  which includes a shovel  292 . 
         [0118]    As will be appreciated the machine  210  is a back hoe loader. Operation of the arm assembly  218  (known as the back hoe) is similar to the operation of the arm assembly  18  of the machine  10 . Operation of the front loader arm  290  and shovel  292  is well known in the art, but in summary hydraulic rams are able to lift and lower the front loader arm  290  and further hydraulic rams are able to “crowd” or “dump” shovel  292  relative to the front loader arm  290 . 
         [0119]    As described above, the thumb  100  is mounted on the dipper  22  of the machine  10 . The thumb  100  may also be mounted on the dipper  222  of the machine  210 . 
         [0120]    As mentioned above, the machine  10  is an excavator and machine  210  is a backhoe loader, though the invention is equally applicable to other types of material handling machines, for example tele-handlers. 
         [0121]    As described above, the pair of lugs  112 A,  112 B are welded on the mounting plate  110 . In alternative embodiments the bracket may be cast in the shape described. 
         [0122]    As described above the flanges  72 ,  74  of the second plate  66  are of a generally uniform width. In alternative embodiments, each of the flanges may comprise a pair of lugs, each lug having at least one hole and the pair of lugs being connected by a lip that is formed when one of the side walls is welded to the first and second plates.