Abstract:
A fastening device and method for mounting equipment to a framing member. The invention includes a single breakaway fastener that is pretentioned using a biasing member to fracture on a predetermined force applied to the fastened joint to avoid damage to the secured equipment. In one example the device and method includes the fastener having a reduced diameter portion that is positioned between an annular plate and the framing member.

Description:
RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 12/819,435, filed on Jun. 12, 2010 which is a divisional of U.S. patent application Ser. No. 11/768,482, filed on Jun. 26, 2007, now U.S. Pat. No. 7,784,665 issued Aug. 31, 2010, which is a continuation-in-part of U.S. patent application Ser. No. 11/451,522, filed on Jun. 12, 2006, now U.S. Pat. No. 7,271,367 issued Sep. 18, 2007. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a production line framing apparatus for clamping and thereafter welding a loosely assembled vehicle body and more particularly to a framing apparatus that accurately positions and locates predetermined areas of a loosely assembled vehicle body at a welding station for accurately clamping and welding the vehicle body together with a high degree of repeatability between consecutive vehicle bodies on the production line, and yet more particularly to a single retainer mounted riser for use on the framing apparatus. 
       BACKGROUND OF THE INVENTION 
       [0003]    The construction of a unitized vehicle body commences with the formation of individual major body panels by stamping the panels from sheet metal blanks. Typically these major panels include a floor panel, right and left body side panels, a fire wall and either a roof panel or transversely extending header members to which a roof panel is subsequently mounted. After the individual panels are stamped, some preliminary assembly operations may then be performed on the individual panels such as, for example, adding door hinge and latch hardware at the body side panels at appropriate locations proximate the door opening, adding seat mounting brackets, adding reinforcements to the body panel, etc. 
         [0004]    Next a set of panels that together constitute a sub-assembly of the finished vehicle body is loosely assembled together. This initial loose assembly of panels frequently is accomplished by a “toy tab” arrangement in which one or more panels is formed with a tab which projects from an edge and which is received in a slot in an adjacent panel. This technique interlocks the panels and frame members to each other to thereby form a preliminary loosely assembled vehicle body wherein the panels and frame members will not separate from each other but wherein the panels and frame members are free to tilt or otherwise move relative to one another. This initial loosely-assembled subassembly is then brought, as for example by a pallet riding on rails, to a welding station where the various panels and frames are welded to each other in a rigid permanently assembled relationship. This initial welding operation step at the welding station is one of the most important steps in the assembly of the vehicle body because it establishes the final welding alignment of all of the various panels and headers relative to each other which is essential to subsequent assembly operations performed on the sub-assembly. During the welding operation it is desirable that the various panels and headers be precisely and accurately located and aligned relative to one another and be held fixedly in the desired position. The positioning of the various panels and header members during the welding operation at the welding station is accomplished utilizing a framing apparatus located at the welding station and including a plurality of gates. For example, a pair of side gates may be utilized in combination with a top gate with the gates moveable between retracted positions, to allow the entry of the vehicle assembly into the welding station, and working positions wherein tooling members carried by the gates suitably engage the assembled body panels to fix them into desired finalized positions whereafter programmable welding robots, each provided with a welding gun, perform welding operations on the assembled body components as they are held in place by the gates and the tooling members. 
         [0005]    Prior art welding gates tend to be rather bulky and heavy apparatuses due to the necessity of carrying many and sometimes rather complicated and heavy tooling members and this heavy construction of the gates has necessitated cumbersome and expensive power equipment to move the gates between their retracted and working positions. The bulky and heavy construction of the welding gates has also interfered with the ability of the robots to access the vehicle body components located within the gates. 
         [0006]    In an attempt to reduce the bulk and weight of the gates, gates having an open frame or skeletal structure have been utilized but these open frame structure gates, by their fragile nature, have difficulty in handling all of the heavy tooling members and are subject to damage as a result of inadvertent impact with obstacles. Such impacts may not only damage the gate but may also misalign tooling members carried by the gate with resultant imprecise joinder of the various body panels. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is directed to the provision of an improved framing apparatus for use at a body welding station. 
         [0008]    More particularly, this invention is directed to the provision of a framing apparatus utilizing a relatively light weight gate that is yet capable of handling even very heavy tooling members. 
         [0009]    Yet more particularly, this invention is directed to the provision of a framing apparatus with breakaway provisions to preclude damage to the gate and/or the tooling members in the event of inadvertent encounters with obstacles. 
         [0010]    The body framing apparatus of the invention is intended for use at a welding station and includes a plurality of tooling members for use in positioning components of the body at the welding station for welding, each tooling member being mounted on the framing apparatus by a mounting bracket. Each mounting bracket includes a base for mounting on the framing apparatus and a riser structure mounted on the base by a fastener bolt and mounting a respective tooling member. 
         [0011]    According to the invention, the fastener bolt is part of a fastener bolt assembly including the fastener bolt, an upper annular plate surrounding a head of the fastener bolt, a lower annular plate surrounding a shank of the fastener bolt, a compressible annular spring device positioned in surrounding relation to the bolt shank between the upper and lower plates, a plurality of upper attachment bolts passing downwardly through bores in the upper annular plate for threaded engagement with threaded bores in the lower annular plate, and a plurality of lower attachment bolts passing upwardly through bores in the riser structure for threaded engagement with further threaded bores in the lower annular plate, the head of the fastener bolt bearing against the annular spring device so that, with the bolt passing through the bore in the riser structure for threaded engagement with the base, tightening of the fastener bolt compresses the spring device to pretension the fastener bolt. 
         [0012]    With this arrangement, and according to the methodology of the invention, following breakage of a fastener bolt, the broken portion of the failed bolt may be removed, the replacement bolt assembly, less the lower attachment bolts, may be positioned on the riser with the bolt shank passing downwardly through a central riser aperture, the lower attachment bolts may be passed upwardly through the riser aperture for threaded engagement with the further threaded bores in the lower annular plate, the riser may be positioned on the base with the lower end of the bolt threadably engaging a threaded bore in the base, the bolt may be tightened to compress the spring device and pretension the bolt, and the upper attachment bolts on the upper annular plate may be removed. 
         [0013]    According to a further feature of the invention, each mounting bracket includes a base for mounting on the framing apparatus and each tooling member includes an integral extension arm mounted on and secured to the base. 
         [0014]    According to a further feature of the invention, the extension arm is mounted on the base by a single central fastener bolt and the interface between the extension arm and the base comprises a plurality of contact points arranged in concentric relation with respect to the fastener bolt. 
         [0015]    According to a further feature of the invention, the contact points are defined by spherical members positioned at the interface. 
         [0016]    According to a further feature of the invention, there are three equally angularly spaced spherical members. 
         [0017]    According to a further feature of the invention, each spherical member comprises a ball. 
         [0018]    According to a further feature of the invention, the fastener bolt includes a reduced diameter portions sized to breakaway in response to a predetermined impact. 
         [0019]    According to a further feature of the invention, the spherical members are carried by the base. 
         [0020]    According to a further feature of the invention, the spherical members are each received in a spherical socket defined in the base. 
         [0021]    Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0023]      FIG. 1  is a schematic view of a motor vehicle framing production line including a framing station; 
           [0024]      FIG. 2  is a schematic cross-sectional view of the framing station; 
           [0025]      FIG. 3  is a side elevational view of a gate utilized at the framing station; 
           [0026]      FIG. 4  is a perspective view of the gate viewed from below the gate; 
           [0027]      FIG. 5  is a perspective view showing an example of a base mounted to a framing gate member; 
           [0028]      FIG. 6  is a perspective exploded view of a mounting bracket with a base in combination with a riser for mounting on the base; 
           [0029]      FIG. 7  is a side elevational view of the base and riser; 
           [0030]      FIG. 8  is a cross-sectional view taken on line  8 - 8  of  FIG. 7 ; 
           [0031]      FIG. 9  is a top view of the base and riser; 
           [0032]      FIG. 10  is a cross-sectional view taken on line  10 - 10  of  FIG. 9 ; 
           [0033]      FIG. 11  is a front elevational view of the base and riser; 
           [0034]      FIG. 12  is a detail view taken within the circle  12  of  FIG. 10 ; 
           [0035]      FIG. 13  is a perspective view of the base and riser shown in association with a tooling member; 
           [0036]      FIGS. 14 and 15  are fragmentary views illustrating the manner in which the invention accommodates production variances or tolerances utilizing a simple bolt; 
           [0037]      FIGS. 16 and 17  are fragmentary views illustrating the manner in which the invention accommodates production variances using a breakaway bolt structure; 
           [0038]      FIG. 18  is a cross-sectional view taken on line  18 - 18  of  FIG. 9 ; 
           [0039]      FIG. 19  is a detail view taken within circle  19  of  FIG. 18 ; 
           [0040]      FIG. 20  is a fragmentary perspective view of the underface of the riser; 
           [0041]      FIG. 21  is a fragmentary elevational view of the riser; 
           [0042]      FIG. 22  is a cross-sectional view taken on line  22 - 22  of  FIG. 21 ; 
           [0043]      FIG. 23  is a bottom view of the riser; 
           [0044]      FIG. 24  is a perspective view of an alternate form of a mounting bracket; 
           [0045]      FIG. 25  is a cross-sectional view taken on line  25 - 25  of  FIG. 24 ; 
           [0046]      FIG. 26  is an exploded cross-sectional view of the mounting bracket of  FIG. 24 ; 
           [0047]      FIG. 27  is a sectional schematic view of a bolt assembly utilized in the mounting bracket of  FIG. 24 ; 
           [0048]      FIG. 28  is a plan view of the base of the mounting bracket of  FIG. 24 ; 
           [0049]      FIG. 29  is a fragmentary cross-sectional view taken on line  29 - 29  of  FIG. 28 ; 
           [0050]      FIG. 30  is a perspective view of a socket pin utilized in the mounting bracket of  FIG. 24 ; 
           [0051]      FIG. 31  is a bottom view of the socket pin; 
           [0052]      FIG. 32  is a perspective view of a further alternate form of a mounting bracket; 
           [0053]      FIG. 33  is an exploded view of the mounting bracket of  FIG. 32 ; 
           [0054]      FIG. 34  is an exploded view, in cross section, of the mounting bracket of  FIG. 32 ; 
           [0055]      FIG. 35  is a cross-sectional view of a bolt assembly utilized in the mounting bracket of  FIG. 32 ; 
           [0056]      FIG. 36  is a cross-sectional view of the mounting bracket of  FIG. 32 ; 
           [0057]      FIGS. 37 ,  38  and  39  are detail views of socket pins utilized in the mounting bracket of  FIG. 32 ; 
           [0058]      FIGS. 40-44  are views of a replacement breakaway bolt assembly suitable for use with any of the bracket embodiments; and 
           [0059]      FIG. 45  is a perspective fragmentary view of a mounting bracket in which the riser is constituted by an integral extension arm of the tooling member. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0060]    With reference to  FIG. 1  an initial loosely assembled body subassembly seen generally at  10  is brought, as for example by a pallet  12  riding on rails  14 , to a welding station  16  where the various panels and frames are welded to each other in a rigid permanently assembled relationship. The positioning of the various panels and header members during the welding operation at the welding station is accomplished utilizing a framing apparatus  15  including a plurality of gates. For example, as seen schematically in  FIG. 1 , a pair of side gates  18  and  20  may be utilized in combination with a top gate  22  with the gates moveable between retracted positions seen in  FIG. 1 , to allow the entry of the vehicle assembly  10  into the welding station, and working positions seen in  FIG. 2 , wherein tooling members carried by the gate suitably engage the assembled body panels to fix them into desired finalized positions whereafter programmable welding robots  26 , each provided with a welding gun  28 , perform welding operations on the assembled body components as they are held in place by the gates  18 ,  20  and  22  and the tooling members  24 . 
         [0061]    The framing apparatus of the invention uses an open frame gate structure  30  ( FIGS. 3-4 ) in combination with a plurality of mounting bracket structures  32  to facilitate attachment of the tooling members to the gate. Gate  30 , which may comprise either a top gate or a side gate, has an open frame skeletal structure comprising skeletal, parallel, longitudinal side members  34 , skeletal end cross-members  36 , skeletal intermediate cross-members  38 , a central robot mounting plate  40 , skeletal upper parallel side rails  42 , skeletal upper cross-members  44 , and lattice members  46  interconnecting each upper side rail to the respective lower rail. All of the members of the frame are preferably formed of a lightweight tubular material of rectangular cross-section having a wall thickness of, for example,  60  thousandths of an inch and all of the members are formed of a suitable ferrous material. The frame components are secured together by welding utilizing suitable gussets. 
         [0062]    Each mounting bracket structure  32  ( FIG. 6-23 ) includes a base  50 , a riser  52 , and a bolt structure  54 . Base  50  may be formed as a cast ferrous structure and includes a planar platform portion  50   a  and a plurality of legs  50   b  integrally downstanding from the platform portion. Platform portion  50   a  may have a generally circular configuration and legs  50   b  are positioned at circumferentially spaced locations on the outer periphery of the platform portion and each extend downwardly from a lug  50   c  formed integrally with the platform portion. Each leg  50   b  has a right angle cross-sectional configuration and a through bore  50   d  is formed in each lug  50   c  outboard of the respective leg. The platform portion and legs are configured and dimensioned such that the base  50  may be positioned over a skeletal frame member such for example as frame member  34  as best seen in  FIG. 5 . As shown, the base may be positioned over the top of a skeletal member  34  as seen on the left side of  FIG. 5  or over the side of the member  34  as seen on the right side of  FIG. 5 . 
         [0063]    The platform portion  50   a  of each base has a wheel like configuration including an outer rim  50   e , a central hub  50   f  having a threaded central bore  50   g  positioned proximate the geometric center of platform portion  50   a , a plurality of circumferentially spaced lugs  50   h  on the inner periphery of the rim, and a plurality of circumferentially spaced spokes  50   i  interconnecting the lugs  50   h  and the hub  50   f . Lugs  50   c  will be seen to be on the outer periphery of rim  50   e  and circumferentially staggered with respect to the inner peripheral lugs  50   h . It will be seen that the ring shaped upper face  50   j  of rim  50   e , as well as the upper face of lugs  50   h , are spaced above the level of spokes  50   i  and hub  50   f . That is, the upper face of spokes  50   i  and hub  50  are recessed with respect to the upper face  50   j  of rim  50   e  so that the upper face  50   j  of the rim presents a well defined ring shaped upwardly facing mounting surface. 
         [0064]    Each riser  52  is formed as an aluminum extrusion and has a circular cross-sectional configuration including a circular outer rim  52   a , a central core structure  52   s  defining a central bore  52   b  positioned proximate the geometric center of the riser, a plurality of sector passages  52   c  spaced circumferentially about bore  52   b , relatively thin aligned spokes  52   d , relatively thick aligned spokes  52   e , and passages  52   f  in spokes  52   e  on opposite sides of central bore  52   b.    
         [0065]    Following the extrusion operation, the riser is cut to length (for example 300 mm), machined along a plane  56  ( FIGS. 21 and 22 ) extending parallel to the central axis of bore  52   b  to the level  58  to form a mounting face  60  parallel to and offset from the central axis and a clamping surface  61  perpendicular to the central axis, further machined along the lines  62  to the plane  63  to form a bolt face  64  coextensive with clamping surface  61  and constituting the lower boundary of a pocket  65 , further machined at the lower face of the extrusion ( FIG. 23 ) to recess the spokes  52   d  and  52   e  with respect to rim  52   a  so that the rim  52   a  presents a distinctly defined downwardly facing ring surface  52   g , further machined to form transverse bolt holes  52   h  opening in face  60 , further machined to form transverse dowel holds  52   i  opening in face  60 , and further machined to form blind axial dowel holes  52   j  opening in the lower face of the riser in spokes  52   e  outboard of passages  52   f  and inboard of ring surface  52   g.    
         [0066]    Bolt structure  54 , as seen in  FIGS. 10 ,  11 ,  14 ,  15  and  18  comprises a bolt  66 , a washer  68  and a lock washer  70 . Bolt  66  includes a head  66   a , a smooth shank  66   b  and a threaded shank  66   c . Alternatively, where a breakaway provision is desired, and as seen in  FIGS. 16 and 17 , bolt structure  54  may include a bolt  72 , a washer  74  and a lock washer  76 . Bolt  72  includes a tightening head  72   a , a reduced diameter head portion  72   b , a smooth shank portion  72   c , a reduced diameter breakaway portion  72   d , and a threaded shank portion  72   e.    
         [0067]    It will be understood that one or more bracket structures  32  are positioned on one of the skeletal members of the frame structure at any location along the frame structure where it is desired to position a tooling member to engage a body component. The tooling member, which may typically comprise a clamp, is seen schematically at  78  in  FIG. 13 . 
         [0068]    In use, a base member  50  is positioned over a skeletal member of the frame with the legs in straddling relation to the skeletal member and the underface of the platform portion of the base positioned against the skeletal member whereafter the base is welded to the frame member over the entire U-shaped interfaces between the base and the frame member as defined by the coaction of legs  50   b  and the platform portion  50   a.    
         [0069]    A pair of dowel pins  80  are now press fit in diametrically opposed bores  50   k  in the platform portion of base  50 ; a riser  52  is positioned against the platform portion to pass the exposed upper ends of the dowels into bores  52   j ; and a bolt  66  is passed through the central bore  52   b  of the riser to engage the threaded shank portion  66   c  of the bolt with the threaded bore  50   g  of the platform portion of the base member. Tightening of the bolt, in coaction with washers  74  and  76 , will be seen to engage the bolt head  66   a  with the bolt face  64  and firmly press riser ring surface  52   g  against base ring surface  50   j  to firmly and positively clamp the riser to the base. Since the interface between the riser and the base is only along well defined ring surfaces, the riser will engage the base in a triangulated manner to provide a firm positive inter-engagement as between the riser and the base. It is also critical that the riser dimension between the bolt face  64  and the lower face of the riser be sufficient to insure that the riser structure within the ring surface  52   g  remain rigid and not flex or distort as the bolt is tightened since such flexing or distorting might interfere with the firm positive triangulated inter-engagement of riser surface  52   g  and base surface  50   j . Following mounting of the riser on the base, a tooling member, for example a clamp  78 , may be mounted on the riser utilizing a blade  82  ( FIG. 13 ) fastened to the mounting face  60  of the riser utilizing bolts and dowel pins passing through bolt holes  52   h  and dowel holes  52   i  and through aligned bolt holes and dowel holes in the blade. 
         [0070]    If a breakaway provision is desired, a breakaway bolt  72  is employed, the bolt is tightened utilizing head  72   a  until the bolt head seats against the bolt face  64 , and further torque is applied to the bolt by the head  72   a  until the reduced diameter portion  72   b  shears. It will be understood that reduced diameter portion  72   b  is designed to shear before reduced diameter portion  72   d  and that the tightening of the bolt structure until the reduced diameter portion  72   b  shears has the effect of pretorquing the bolt to the torque level required to shear the reduced diameter portion  72   b . In use at the framing station, each open frame gate structure  30  is positioned by a robot which is secured to robot mounting plate  40  and programmed is known manner. Ideally, the robot moves the gate into position at the framing station without encountering any obstacles and therefore without damaging the tooling members or, more importantly, the delicate frame structure. However, if an obstacle is encountered, the obstacle will typically exert a force F against the vertical portion of a riser which in turn will cause the riser to tilt which in turn will result in shearing or rupture of the reduced diameter bolt portion  72   d  which in turn will allow the riser and associated tooling member to breakaway from the base  50  and preclude twisting or other damage to the delicate frame structure  30  and/or dislocation of the tooling member carried by the riser with consequent mis-assembly of the respective automotive body components. The defined inter-engaging ring surfaces on the riser and the base have the effect of defining a locus of points equal distant from the center line of the breakaway bolt  72  so that no matter in which direction the impact F is exerted on the riser vertical portion the same moment will be applied to the riser and to the bolt structure and the same force F will result in an identical rupture pattern with respect to the reduced diameter bolt structure portion  72   d.    
         [0071]    The single central mounting bolt in combination with the dowel pins  80  provides a firm, positive locating of the riser on the base and the defined ring surface interface between the lower face of the riser and the upper face of the base insures a firm positive triangulated mounting of the riser on the base. As compared to a prior art riser mounting arrangement employing four quadranted bolt holes with dowel holes positioned between the bolt holes, the invention riser mounting system employs a single central bolt hole, a single central bolt and a pair of flanking dowel pins providing considerable savings in both materials and labor. The invention riser, by virtue of its extruded construction, also provides significant material savings as compared to prior art risers and the invention riser, by virtue of its aluminum extrusion formation, provides considerable weight savings as compared to prior art risers. 
         [0072]    The illustrated and described base and riser structure also allows ready provision to accommodate production variances or tolerances. Specifically, as best seen in a comparison of  FIGS. 14 and 15  and  FIGS. 16 and 17 , production variances or tolerances can readily be accommodated by adjusting the position of bore  50   g  within hub  50   f  and, in this respect, base ring surface  50   j  preferably has a greater width than riser ring surface  52   g  so that ring surface  52   g  may adjust on surface  50   j  in response to movement of bore  52   g  within hub  50   f  without interfering with the firm positive triangulated inter-engagement of the ring surfaces. 
         [0073]    Especially in installations employing a breakaway bolt structure, the bores  52   d  in the lugs  50   c  may be utilized to anchor cables to tether the riser to the base to limit the movement of the riser relative to the base in the event of a breakaway. 
         [0074]    The alternate mounting bracket construction seen in  FIGS. 24-31  includes a riser  100 , a base  102 , and a fastener assembly  103 . 
         [0075]    Riser  100  includes a riser portion  100   a  and a rectangular platform portion  100   b . Platform portion  100   b  includes a central unthreaded aperture  100   c.    
         [0076]    Base  102  includes a circular platform portion  102   a  and a plurality of circumferentially spaced legs  102   b  extending integrally from the platform portion for straddling, welded mounting on a skeletal member of the frame structure as described with respect to the  FIGS. 1-23  mounting bracket construction. Circular platform portion  102   a  includes a central threaded aperture  102   c.    
         [0077]    Riser  100  is mounted and located on the base  102  utilizing fastener assembly  103  and a plurality of spherical members positioned at the interface between the riser and the base in concentric surrounding relation to the central axis of apertures  100   c  and  102   c . Specifically, riser  100  is mounted on the base  102  utilizing three balls or spheres  104 , provided on the upper face  102   d  of the base platform portion  102   a  in concentric relation to aperture  102   c  and at equal 120° spacing (see also  FIGS. 28 and 33  which illustrate such spacing), seating in three V-shaped locating socket grooves  106  provided in the lower face  100   d  of the riser platform portion in concentric relation to aperture  100   c , at equal 120° spacing, and in vertical alignment with respective balls  104 . 
         [0078]    Each locating socket groove  106  is defined by a socket pin  108 . Each socket pin  108  includes a circular locator portion  108   a  and a main body or base portion  108   b . The socket groove  106  is defined in the lower face of main body portion  108   b  and, specifically, is defined by two outwardly splayed flat surfaces  108   c  opening in the lower annular face  108   d  of the main body portion  108   b  with a notch  108   e  defined at the upper converging edges of the flats  108   c.    
         [0079]    Each socket pin  108  is fitted in a bore in the platform portion  100   b  of the riser  100  and, specifically, the locator portion  108   a  of the pin is fitted in a bore  100   e  in the riser platform portion and the base portion  108   b  is fitted in a counter bore  100   f  in the riser platform portion. Each pin may be press fit in the respective bore of the riser with the lower face  108   d  of the pin spaced or recessed upwardly with respect to the lower face  100   d  of the riser platform portion and the upper face  108   f  of the pin recessed or spaced downwardly from the upper face  100   g  of the riser platform portion. Each groove  106  defines a central axis  109  and the pins  108  are positioned in the bores  100   f  such that all of the axes  109  pass through the center of central aperture  100   c.    
         [0080]    Each ball or sphere  104  is positioned in a spherical socket  102   e  in the base platform portion with the center  104   a  of the sphere positioned below the upper face  102   d  of the base to preclude displacement of the ball from the base. The ball may be swively mounted in the base or may be fixedly secured in the base and may be mounted in the base by any known procedure including depositing the ball in a frozen condition into the socket  102   e  and then allowing the ball to expand to fixedly fill the socket. Each ball  104  and respective socket pin  108  are configured and dimensioned such that the ball  104  and socket groove  106  contact each other only at two points  110 . 
         [0081]    Fastener assembly  103  includes a fastener bolt stud  114 , a nut  116 , a plurality of stacked Belleville washers  118 , and a retainer cup  120 . In the assembled relation of the riser and base, the bolt stud  114  passes through the central unthreaded bore  100   c  in the riser platform portion for threaded engagement with the threaded central bore  102   c  in the base platform portion with the nut  116  pressing downwardly against the stacked Belleville washers  118  retained within cup  120  to press the riser against the base. The various parameters are chosen such that with the riser engaging the balls  104  at the total of six points  110 , a clearance is defined between lower riser platform portion face  100   d  and upper base platform portion face  102   d  of, for example, 10 mm 
         [0082]    Bolt stud  114  includes a O-Ring groove  114   a  and a reduced diameter breakaway groove  114   b.    
         [0083]    It will be understood that, in use, a tooling member such as a clamp  78  will be attached to the upper end of the riser portion  100   a  of the riser in the manner previously described with respect to the  FIGS. 1-23  embodiment. 
         [0084]    Whereas the embodiment of  FIGS. 24-31  has been described as including balls mounted in the base seating in V-shaped grooves provided in the riser, this arrangement can be reversed with the balls being provided in the lower face of the riser and the V-shaped grooves being provided in the upper face of the base with the specific arrangement determined by the requirements of any particular application. 
         [0085]    Rather than Belleville washers shown as part of the bolt assembly, springs or a urethane block may also be employed for the same purpose. The Belleville washer/spring/urethane block provision allows the assembly to maintain rigidity even when the fastener is being stretched as well as providing a “shock absorbing” aspect in case of collision. 
         [0086]    The arrangement of  FIGS. 24-31  enables breaking of the bolt stud  114  at the shear point  114   b  when the riser is subjected either to bending, tortional loading or shear loading. The three locator configurations, with the ball/groove arrangement provided 120° apart, creates three distinct axes of pivoting defined by the centers of two spheres/balls providing a consistent lever from the center of the fastener, and a consistent shear behavior, irrespective of the location or direction of the impact against the riser. The arrangement of  FIGS. 24-31  provides a firm triangulated interface between the base and riser and provides excellent repeatability for mounting the riser to the base since the three spheres may be seated in the grooves in only one precise configuration. 
         [0087]    The alternate mounting bracket construction seen in  FIGS. 32-39  includes a riser  200 , a base  202  and a fastener assembly  203 . 
         [0088]    Base  202  corresponds generally to the base  102  of the  FIGS. 24-31  embodiment and includes a circular platform portion  202   a  and a plurality of circumferentially spaced legs  202   b  extending integrally from the platform portion for straddling welded mounting on a skeletal member  34  of the frame structure as described with respect to the  FIGS. 1-23  mounting bracket construction. 
         [0089]    Circular platform portion  202   a  includes a central threaded aperture  202   c  and three balls or spheres  204  are provided on the upper face  202   d  of the platform portion in concentric relation to central aperture  202   c  and at equal 120° spacing. Each ball  204  is positioned in a spherical socket  202   e  in the platform portion with the center  204   a  of the sphere positioned below the upper face  202   d  to preclude displacement of the ball from the base. The ball may be swively mounted in the base or may be fixedly secured in the base and may be mounted in the base by any known procedure including depositing the ball in a frozen condition into the socket  202   e  and then allowing the ball to expand to fixedly fill the socket. 
         [0090]    Riser  200  includes a tubular member  206 , a plurality of socket pins  208  and an annular plate  210 . 
         [0091]    Tubular member  206  may be formed as an extrusion and may include a main body tubular portion  206   a  defining a central axial bore  206   b  and a plurality of circumferentially spaced external rib portions  206   c  each defining an axial bore  206   d.    
         [0092]    A bore  206   e  is provided at the lower end  206   f  of the riser in coaxial counter-bore relation to each axial bore  206   d . External rib portions  206   c  will be seen to define flat faces  206   g  to facilitate the attachment of a suitable tooling member  78 . 
         [0093]    Each socket pin  208  includes a pilot portion  208   a  for press fit in a respective bore  206   e  and a main body portion  208   b  defining a groove  208   c  for seating a respective ball  204 . 
         [0094]    Each groove  208   c  has a bowl shaped configuration and defines two outwardly splayed flat surfaces  208   d  with a notch  208   e  defined at the upper converging edges of the flats  208   d . Each groove  208   c  defines a central axis  211  and the pins  208  are positioned in the bores  206   c  such that all of the axes  211  pass through the central axis of threaded aperture  202   c.    
         [0095]    Each ball  204  and respective socket pin  208  are configured and dimensioned such that the ball  204  and the socket groove  208   c  contact each other only at two points  212 . 
         [0096]    Annular plate  210  is positioned in bore  206   b  proximate the lower riser end  206   f  on a sill or shoulder  206   h  and defines a central unthreaded aperture  210   a.    
         [0097]    Fastener assembly  203  includes a breakaway fastener bolt  214  and a stack of Belleville washers  216 . 
         [0098]    Belleville washers  216  are positioned on plate  210  in concentric relation to aperture  210   a  and the shank  214   a  of breakaway bolt  214  passes downwardly through the Belleville washers and through aperture  210   a  with the head  214   b  of the bolt pressing downwardly on the stack of Belleville washers and the threaded lower end  214   c  of the bolt threadably engaging the threaded central aperture  202   c  in base platform portion  202   a.    
         [0099]    In use, the riser is positioned on the base with the grooves  208   c  seating on the balls  204  at a total of six defined points  212 , whereby to positively locate and position the riser on the base, whereafter bolt  214  is tightened to threadably advance the threaded lower end  214   c  into base central aperture  202   c  whereby to compress the Belleville washers and place the bolt in pretension so that any significant impact against the riser will have the effect of shearing the breakaway bolt at the reduced diameter portion  214   d.    
         [0100]      FIGS. 40-44  illustrate a breakaway bolt assembly replacement kit  300  which may be used with any of the previously described mounting bracket structures to facilitate the replacement of a broken breakaway bolt. Kit  300  is hereafter described with reference to the mounting bracket structure of  FIGS. 24-31  but, as noted, may also be readily utilized with appropriate modification with the mounting bracket structures of  FIGS. 1-23  or  FIGS. 32-39 . 
         [0101]    Kit  300  includes a fastener bolt  302  having a head  302   a , a shank  302   b , a reduced diameter portion  302   c  and a threaded lower end  302   d ; an upper annular plate  304  having a central aperture  304   a  surrounding the head  302   a  of the fastener bolt; a lower annular plate  306  having a central bore  306   a  surrounding the shank  302   b  of the fastener bolt; a stack of Belleville washers  308  positioned in surrounding relation to the bolt shank portion  302   b  between the upper and the lower plates; a plurality of upper attachment bolts  310  passing downwardly through unthreaded bores  304   b  in the upper annular plate for threaded engagement with threaded bores  306   b  in the lower annular plate; and a plurality of lower attachment bolts  312  sized to pass upwardly through unthreaded apertures  100   h  in the riser platform portion  100   b  for threaded engagement with further threaded bores  306   c  in lower plate  306 . 
         [0102]    In use of the kit with the bracket structure of  FIGS. 24-31 , and following breakage of a fastener bolt at a reduced diameter portion in response to a predetermined impact against the riser, the broken portions of the failed bolt may be removed from the riser and from the base whereafter the kit  300 , minus the lower attachment bolts  312 , may be positioned on the riser  100   b  with the bolt shank passing downwardly through riser central aperture  100   c , whereafter the lower attachment bolts  312  may be passed upwardly through riser apertures  100   h  for threaded engagement with threaded bores  306   c  in the lower plate, whereafter the riser may be positioned on the base with the lower threaded portion  302   d  of bolt  302  threadably engaging threaded base aperture  102   c  and grooves  106  seating on balls  104 , whereafter the bolt may be tightened to compress the Belleville washers  308  to pretension the bolt (for example to 10 ft. lbs.) whereafter the upper attachment bolts  310  and the upper plate  304  may be removed and discarded. The system is now ready for production. 
         [0103]    As best seen in  FIGS. 41-43  an alternate method of using a pre-stressed or pre-tensioned breakaway bolt assembly  300  is described. In the example, a spring member in the form of a stack of Belleville washers  308 , are positioned between upper plate  304  and lower plate  306 . As best seen in  FIG. 41 , upper attachment bolts  310  are passed axially passed through unthreaded bores  304   b  and advancingly and threadingly engaged in threaded bores  306   c  in lower plate  306  to axially compress spring member  308  as shown. Once compressed, fastener bolt  302  is axially positioned through upper plate  302 , spring member  308  and lower plate  306  with threaded portion  302   d  and narrowed diameter portion  302   c  axially extending below lower plate  306 . Alternately, fastener bolt  302  may be positioned through the upper and lower plates and spring member  308  prior to advancing upper attachment bolts  310  to compress the spring member  308 . In this state as best seen in  FIG. 41 , where spring member  308  is compressed by upper attachment bolts  310 , fastener assembly  300  is are ready to be attached to, for example, a riser  100   b  as shown in  FIG. 44  or a portion of a tooling member such as a riser arm  78   a  shown in  FIG. 45 . 
         [0104]    As best seen in  FIGS. 43 and 44  and described above, following compression of spring member  308 , fastener bolt  302  threaded portion  302   d  can be threadingly engaged with a riser  100   b  or tooling member extension arm  78   a . In this example, minimal torque need be applied to fastener bolt  302  as spring member  308  is already compressed. As described above, in order to apply at least some of the pretension built up in spring member  308 , upper attachment bolts  310  are removed causing the spring member, for example Belleville washers  308 , to axially expand to release some of the potential energy. In a preferred example, on removal of upper attachment bolts  310 , upper annular plate  304  can also be removed as there is radial space between the bolt head  302   a  and upper plate  304 . At least a portion of the pre-tension energy of spring member  308  is transferred to fastener  302  through abutting contact of spring member  308  to the fastener head  302   a  thereby pre-stressing or pre-tensioning breakaway fastener  302 . With the upper attachment bolts  310  and upper plate  304  removed, fastener assembly  300  takes the form of fastener assembly  203  as generally shown in  FIGS. 35 and 36 . 
         [0105]    In the example shown in  FIGS. 43 and 44 , lower attachment bolts  312  may be used to positively attach lower plate  306  to the tooling members or framing member as described above and illustrated. On fracture of the breakaway bolt  302 , the lower plate  306  remains secured to the riser  100   b  or other component connected thereto. 
         [0106]    In the bracket structure of  FIG. 45 , the riser, rather than being constituted by a discreet member, is constituted by an integral extension blade or arm of the tooling member. 
         [0107]    The mounting bracket of  FIG. 45  includes a riser arm  78   a , a base  402 , and a fastener assembly  404 . 
         [0108]    Riser arm  78   a  is constituted as an integral extension arm of a tooling member  78 . 
         [0109]    Base  402  corresponds generally to base  102  and base  202  and includes a circular platform portion  402   a  and a plurality of circumferentially spaced legs  402   b  extending integrally from the platform portion for straddling welded mounting on a skeletal member of the frame structure. 
         [0110]    Base platform portion  402   a  includes a central threaded aperture (not shown) and three balls or spheres  406  are provided in the upper face  402   d  of the platform portion in concentric relation to the central aperture and at equal 120° spacing. Each ball is positioned in a sphere socket in the platform portion with the center of the ball positioned below the upper face  402   d  to preclude displacement of the ball. 
         [0111]    Riser arm  78   a  mounts a plurality of equally circumferentially spaced socket pins  408  for coaction with balls  406  in the manner previously described with respect to the mounting brackets of  FIGS. 24-31  and  FIGS. 32-39 . 
         [0112]    Fastener assembly  404  corresponds to the fastener assembly  203  of the  FIG. 32-39  mounting bracket embodiment and includes a breakaway fastener bolt  410 , including a reduced diameter portion, and a stack of Belleville washers  412 . 
         [0113]    In use, the riser arm is positioned on the base with the grooves defined by the socket pins seating on the balls at a total of six defined points, whereby to positively locate and position the riser on the base, whereafter bolt  410  is tightened to threadably advance the threaded lower end of the ball into the base central aperture whereby to compress the Belleville washers  412  and place the bolt in pretension so that any significant impact against the riser arm will have the effect of shearing the bolt at the reduced diameter portion. 
         [0114]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law. For example, although several embodiments of the mounting bracket have been described as including a specific discreet riser member, it will be understood as shown for example in the  FIG. 46  embodiment, that the riser may instead be constituted by an integral extension blade or arm of the associated tooling member and the term riser or riser structure as used in the claims will be understood to include not only a discreet riser member, but also a riser formed as an integral extension arm of an associated tooling member.