Abstract:
A tripod is provided for mounting a machine gun between a front pintle and a traverse-and-elevation (T&amp;E) device, being mechanically alterable between stowage and deployment configurations by means of a curved traverse bar. The tripod includes a head member for receiving the front pintle, a fore leg, first and second rear legs, and the traverse bar. The fore leg connects to the head member at a fore pitch hinge, and extends in the deployment configuration and folds aft beneath the head member in the stowage configuration. The first and second rear legs connect to the head member by corresponding rear lateral hinges. Each rear leg has a rail member that slides longitudinally therealong. The rear legs splay outward from the head member in the deployment configuration and contract substantially parallel in the stowage configuration. The traverse bar includes an elongated member for mounting the T&amp;E device, first and second terminals at opposite ends of the elongated member, and a sprocket. The elongated member has an arc curvature that enables the T&amp;E device to travel along the elongated member with constant elevation of the machine gun. The terminals respectively attach to the first and second legs by respective orifices. The first terminal includes a circular serrated cavity to receive the sprocket that has the first pivot orifice being offset from its axial center. The sprocket is removable to rotate the first pivot orifice for subsequent reinsertion into the serrated cavity.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The invention is a Continuation-in-Part, claims priority to and incorporates by reference in its entirety U.S. patent application Ser. No. 14/752,707 filed Jun. 26, 2015 and assigned Navy Case 103685. 
     
    
     STATEMENT OF GOVERNMENT INTEREST 
       [0002]    The invention described was made in the performance of official duties by one or more employees of the Department of the Navy, and thus, the invention herein may be manufactured, used or licensed by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
       BACKGROUND 
       [0003]    The invention relates generally to lock and release legs on a machine gun tripod while enabling level sweep. In particular, the invention relates to a traverse bar to secure a tripod&#39;s rear legs and support a traverse-and-elevation mechanism for a machine gun. 
         [0004]    The United States Army (USA) and United States Marine Corps (USMC) have used the M122 machine gun tripod since about 1935, which provides a more stable and versatile platform for accurate and controlled angular sweep during successive firings than available by the bipod mounted to a standard M240 machine gun. 
         [0005]      FIG. 1  shows an isometric view  100  of a conventional M122 tripod and its main components, including the tripod stand  110 . A mounting head  120  includes a pintle bushing  125  into which a front yoke (not shown) can be inserted. A front leg  130  with front foot pad attaches to the head  120 . The tripod  110  also includes a pair of rear legs extending from the head  120 : rear starboard leg  140 , and rear port leg  150 . The starboard and port legs  140  and  150  connect together by a traverse bar  160  to maintain fixed angular separation. 
         [0006]    A traverse-and-elevation (T&amp;E) mechanism (not shown) attaches to the traverse bar  160  to adjust the firing direction of the gun M240. The conventional traverse bar  160  is typically straight and connects to each rear leg by a sleeve  170 , which for the starboard leg  140  includes a clamp  175  to secure and release the traverse bar  160 . A compass rose  180  indicates orientation, with the rightward longitudinal axis denoting forward direction, upward elevation axis denoting upward vertical direction, and diagonal lateral axis denoting port side direction. The conventional M122 tripod weighs 12.3 lb alone. 
       SUMMARY 
       [0007]    Conventional traverse support mechanisms yield disadvantages addressed by various exemplary embodiments of the present invention. In particular, various exemplary embodiments provide a tripod for mounting a machine gun between a front pintle and a traverse-and-elevation (T&amp;E) device, being mechanically alterable between stowage and deployment configurations by means of a curved traverse bar. The tripod includes a head member for receiving the front pintle, a fore leg, first and second rear legs, and the traverse bar. The fore leg connects to the head member at a fore pitch hinge, and extends in the deployment configuration and folds aft beneath the head member in the stowage configuration. 
         [0008]    The first and second rear legs connect to the head member by corresponding rear lateral hinges. Each rear leg has a rail member that slides longitudinally therealong. The rear legs splay outward from the head member in the deployment configuration and contract substantially parallel in the stowage configuration. The traverse bar includes an elongated member for mounting the T&amp;E device, first and second terminals at opposite ends of the elongated member, and a sprocket. 
         [0009]    The elongated member has an arc curvature that enables the T&amp;E device to travel along the elongated member with constant elevation of the machine gun. The terminals respectively attach to the first and second legs by respective pivot orifices. The first terminal includes a circular serrated cavity to receive the sprocket with the first pivot orifice offset from its axial center. The sprocket is removable to rotate the first pivot orifice for subsequent reinsertion into the serrated cavity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    These and various other features and aspects of various exemplary embodiments will be readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings, in which like or similar numbers are used throughout, and in which: 
           [0011]      FIG. 1  is a perspective view of a conventional machine gun tripod; 
           [0012]      FIG. 2  is a perspective assembly view of an exemplary machine gun tripod; 
           [0013]      FIGS. 3A through 3D  are perspective views of the exemplary tripod; 
           [0014]      FIGS. 3E through 3G  are plan views of the exemplary tripod; 
           [0015]      FIG. 4  is plan and elevation views of the exemplary tripod, folded; 
           [0016]      FIG. 5  is an elevation view of exemplary legs for the tripod; 
           [0017]      FIG. 6  is a cross-section view of the exemplary legs; 
           [0018]      FIG. 7  is a perspective view of a first exemplary traverse bar; 
           [0019]      FIG. 8  is a perspective view of a second exemplary traverse bar; 
           [0020]      FIGS. 9A and 9B  are perspective views of the second exemplary traverse bar with an exemplary clamp; 
           [0021]      FIGS. 10A and 10B  are perspective views of port leg joints for the first and second exemplary traverse bars; 
           [0022]      FIG. 11  is a plan view of a primary starboard leg joint for the traverse bar; 
           [0023]      FIG. 12  is a perspective view of a secondary starboard leg joint for the traverse bar; 
           [0024]      FIG. 13A through 13C  are plan views of the primary starboard leg joint at select tension positions; 
           [0025]      FIG. 14A  is an elevation axial view of the exemplary tripod; 
           [0026]      FIG. 14B  is a plan view of the exemplary tripod; 
           [0027]      FIG. 14C  is an elevation lateral view of the exemplary tripod; 
           [0028]      FIG. 15  is a perspective assembly view of the right joint for the third exemplary traverse bar; 
           [0029]      FIG. 16  is a perspective exploded view of the left joint for the first exemplary traverse bar; 
           [0030]      FIGS. 17A and 17B  are perspective assembly and exploded views of the right joint for the third exemplary traverse bar; 
           [0031]      FIG. 18  is a perspective view of the right end for the third exemplary traverse bar; 
           [0032]      FIGS. 19A and 19B  are plan and perspective assembly views of the right end for the first exemplary traverse bar with sprocket insert; and 
           [0033]      FIGS. 20A and 20B  are perspective exploded views of the right end for the first exemplary traverse bar with sprocket insert. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    In the following detailed description of exemplary embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized, and logical, mechanical, and other changes may be made without departing from the spirit or scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
         [0035]    Dahlgren has been tasked to design a replacement yet functional tripod with reduced weight.  FIG. 2  shows a perspective assembly view  200  of an exemplary XM131C Rev C tripod  210  for a machine gun (depicted in application Ser. No. 14/752,707 with incorporation by reference). A mounting head  220  with a front pintle  225  provides the locus for a fore leg  230  with front foot  235 , and angularly splayed rear legs: starboard leg  240  with right foot  245  and port leg  250  with left foot  255 . The machine gun pivots on the tripod  210  at a front yoke mount on the front pintle  225 . An exemplary traverse bar  260  connects the rear legs  240  and  250 . An angular traverse stop clamp  270  (described in application Ser. No. 14/752,707 with incorporation by reference) attaches to the traverse bar  260  to restrict travel of the T&amp;E mechanism (depicted in application Ser. No. 14/752,707) that mounts thereto. The traverse bar  260  includes an elongated section that spans between the rear legs  240  and  250  in an arc that curves to enable the T&amp;E mechanism to sweep the machine gun from side to side while maintaining constant elevation while on a flat surface. 
         [0036]    The fore leg  230  pivotably attaches to the head  220  at a pitch hinge  280 . The rear legs  240  and  250  pivotably attach to the head  220  at respective lateral hinges  290 . The feet pads  235 ,  245  and  255  are designed to penetrate into ground to provide a stable platform from which to fire the machine gun. The weight of the M131C Mod C tripod  210  is 7.4 lb absent pintle  225  and T&amp;E mechanism. Total weight of the exemplary tripod  210  with the pintle  225  and the T&amp;E mechanism is 12.1 lb total. This constitutes an improved reduced weight over the conventional M122 tripod  110  of 12.3 lb without the pintle and T&amp;E mechanism and 18.1 lb total. 
         [0037]    The exemplary tripod  210  is formed substantially from forged aluminum components and the legs  230 ,  240  and  250  form wide flange cross-section structures rather than tubes to reduce weight. Aluminum alloys can include 6061-T6 and 7075-T6, for example. The fore leg  230  has an approximate length of nine inches and is elevated from ground level by 45°, and the rear legs  240  and  250  have approximate lengths of seventeen inches and are elevated from the ground by 20°. The rear legs  240  and  250  are angularly separated by 115°. These dimensions are exemplary for the configuration designed, and are not limiting. 
         [0038]      FIGS. 3A through 3D  show perspective views  300  of the exemplary M131 tripod  310  (including the clamp  270 ). In  FIG. 3A , an exemplary tripod assembly  310  is shown as deployed. A pintle bushing  320  on the head  220  receives the front pintle  270  (shown in  FIGS. 2 and 14A through 14C ). The head  220  includes an aft chamber  330  that enables the rear legs  240  and  250  to rotate within at their respective hinges  290 . The exemplary traverse bar  260  attaches to the starboard leg  240  at a right joint  340  and to the port leg  250  at a left joint  350 . In  FIG. 3B , the tripod assembly  310  is being partially collapsed for stowage and/or transport. Forward and rearward forces cause the right joint  340  and the left joint  350  to slide respectively forward and aft in alternating directions  360 . The right joint  340  also pivots to rotate counter-clockwise (as viewed from above). This action causes the rear legs  240  and  250  to pivot towards each other in converging directions  370  held by their respective hinges  290 . In  FIG. 3C , the rear legs  240  and  250  are furled to be mutually parallel, and the fore leg  230  rotates at its hinge  280  so the front foot  235  moves aft  380 . In  FIG. 3D , the fore leg  230  is folded underneath the head  220 . 
         [0039]      FIGS. 3E through 3G  show plan views  390  of the exemplary M131 tripod. In  FIG. 3E , the tripod  310  is shown as deployed. In  FIG. 3F , the tripod  310  is shown with the traverse bar  260  sliding and rear legs  240  and  250  pivoting towards each other. In  FIG. 3G , the tripod  310  is shown with the rear legs  240  and  250  stowed as mutually parallel. 
         [0040]      FIG. 4  shows plan and elevation views  400  of the exemplary tripod as folded. The fore leg  230  is disposed under the head  220 , and the rear legs  240  and  250  are collapsed as parallel to each other.  FIG. 5  shows an elevation view  500  of exemplary rear leg assemblies  510  and  520  for the tripod. The first M131C tripod embodiment includes a first leg  510  composed of three segments: a proximal segment  530  that attaches to the head  220  at the hinge  290 , an extending member  540  that establishes overall design length, and a proximal segment  550  that includes the foot. The second M131C Rev C tripod  310  embodiment includes a second leg  560  constituting a unitary entity, which can be produced by milling a ⅞″×1¼ aluminum billet, or by forging and finishing. 
         [0041]      FIG. 6  shows cross-section views  600  of the exemplary legs  510  and  520 . A first cross-section  610  with cruciform shape includes top flange  620 , bottom flange  630  and mezzanine flange  640  joined together by a vertical spar  650  for the M131C configuration. Cross-sectional dimensions for the first leg  510  include height of 1.1875 inches and width of 0.875 inch. A second cross-section  660  includes an inner face  670  and an outer face  680  in relation to the opposite leg for the M131C Rev C configuration. Cross-sectional dimensions for the second leg  520  include height of 1.28 inches and width of 0.875 inch. 
         [0042]      FIG. 7  shows perspective views  700  of a first exemplary traverse bar  720 . A right end  720  and a left end  730  are joined by a curved span therebetween having a T-shape cross-section  740 , the curved span including scale marks  750  for setting the position for the T&amp;E mechanism. The ends  720  and  730  each have two clevis prongs to form a pin joint at connections to their respective legs  240  and  250 . 
         [0043]      FIG. 8  shows perspective views  800  of a second exemplary traverse bar  260  shown with the exemplary tripod assembly  210 . The curved span of the traverse bar  260  includes scale marks  810  to denote angles for the T&amp;E mechanism. Right and left ends  820  and  830  are joined by the curved span therebetween having a C-shape cross-section  840 . The right end or terminus  820  includes a serrated (or toothed) circular cavity  850 . The left end or terminus  830  constitutes a tang with a left through-hole  860  to provide a pin joint for connecting to a clevis on its respective leg  250 . The curved segment between the ends can be called an elongated member  870 . 
         [0044]      FIGS. 9A and 9B  show perspective views  900  of the second exemplary traverse bar  260  with an exemplary stop clamp  270  described in application Ser. No. 14/752,707.  FIG. 9A  illustrates the open-ring configuration of the stop clamp  270  engaging the traverse bar  260  with its C-shape cross-section from below.  FIG. 9B  shows the traverse bar  260  connected to the rear legs  240  and  250 . The right end  820  for corresponding joint  340  attaches to a first clevis bracket  910  on the starboard leg  240  and secured by a bolt  920 . The left end  830  for corresponding joint  350  attaches to a second clevis bracket  930  on the port leg  250  and secured by a threaded bolt  940  and accompanying nut. The first clevis bracket  910  is disposed on a starboard slide rail  950  that traverses forward along the length of the starboard leg  240 . 
         [0045]      FIGS. 10A and 10B  show perspective views  1000  of left leg joints  350  for the first and second exemplary traverse bars.  FIG. 10A  illustrates the first traverse bar  710  with its clevis right end  730  attaching to slide rail  1010  by a tang  1020  disposed on the port leg  250 .  FIG. 10B  shows the second traverse bar  260  with its tang right end  830  attaching to a port side rail  1030  by the second clevis bracket  930  disposed on the port leg  250  and secured by bolt  940 . The port side rail  1030  traverses aft along the length of the port leg  250 . 
         [0046]      FIG. 11  shows a plan view  1100  of a first exemplary embodiment of a right end assembly  1110  for the right joint  340 . The assembly  1110  includes the right end  820  of the traverse bar  260  together with a sprocket  1120  that inserts into the corresponding cavity  850  that extends through the right end  820 . The sprocket  1120  includes an off-center circular orifice  1130  to pivot the right joint  340 . This means that the center of the circular orifice  1130  is offset from the axial center of the sprocket  1120 . The right end  820  includes exterior marks  1140 ,  1150  and  1160  for aligning to interior marks  1170  on the sprocket  1120 . Alignment of corresponding marks  1150  and  1170  is exemplified by an enveloped example  1180 . Relative disposition of the offset orifice  1130  in relation to the right end  820  can provide longer or shorter effective span of the traverse bar  260 , with which to adjust tension between the rear legs  240  and  250  that possible deformation under field operations may necessitate. Changing the angular position of the sprocket  1120  within its cavity  850  alters the position of the offset orifice  1130 , and thus the effective distance from the right joint  340  to the mounting hole  860  at the left end  830  at the left joint  350 , thereby enabling span of the traverse bar  260  to be shortened or lengthened. 
         [0047]      FIG. 12  shows a perspective view  1200  of a second exemplary embodiment of a right end assembly  1210  for the right joint  340 . The assembly  1210  includes the right end  820  of the traverse bar  260  together with a sprocket  1220  that inserts into the corresponding cavity  850  that extends through the right end  820 . The sprocket  1220  includes an off-center circular orifice  1230  to pin the right joint  340 . This means that the center of the circular orifice  1230  is offset from the axial center of the sprocket  1220 . The right end  820  includes an exterior mark  1240  that aligns with an interior mark  1250  disposed on the sprocket  1120 . Additional bracketing marks  1260  and  1270  angularly extend in arks  1280  from the exterior mark  1240  from either side along the rim of the right end  820 . An envelope  1290  denotes the alignment of the exterior and interior marks  1240  and  1250  for disposition of the offset orifice  1230 . The alternative configurations of the sprocket  1220  within the cavity  850  are substantially identical to those described with sprocket  1120  to adjust the length of the traverse bar  260 . 
         [0048]    Alternative alignment of the interior mark  1250  to the negative mark  1260  shifts the relative position of the orifice  1230  for the minimum length of the traverse bar  260 . Alternative alignment of the interior mark  1250  to the positive mark  1270  shifts the relative position of the orifice  1230  for the maximum length of the traverse bar  260 , to compensate for tensile-induced deformation at the hinges  290  on the head  220 . The mark  1250  on the sprocket  1120  and marks  1240 ,  1260  and  1270  on the right end  820  facilitate assembly for default standard positions, as well as providing a reference when adjusting the length of the traverse bar  260 . Exemplary embodiments preferably utilize standard gear sizes for the sprocket  1120  and standard broach sizes for the cavity  850  to facilitate economical manufacture of these components. The scale legend  1280  inscribed into the surface of the right end  820  indicates the rotation direction the insert to either increase or decrease tension between the rear legs  240  and  250 . 
         [0049]      FIGS. 13A through 13C  show plan views  1300  first right end assembly  1110  at select sprocket positions  1310 ,  1320  and  1330  for varying lengths of the traverse bar  260  to adjust tension between the rear legs  240  and  250 .  FIG. 13B  illustrates the first position  1310  that corresponds to view  1100 .  FIG. 13A  shows the second tensile position  1320  with the sprocket  1120  turned counter-clockwise  1340  in the cavity  850  from the first position  1310  so that the orifice  1130  corresponds to the maximum length of the traverse bar  260 .  FIG. 13C  shows the third tensile position  1330  with the sprocket  1120  turned clockwise  1350  in the cavity  850  from the first position  1310  so that the orifice  1130  corresponds to the minimum length of the traverse bar  260 . 
         [0050]      FIGS. 14A through 14C  show views  1400  of the exemplary tripod  210  (excluding the clamp  270 ) as deployed.  FIG. 14A  exhibits the elevation axial view  1410  of the tripod  1410 , including slide rails  950  and  1030 .  FIG. 14B  shows the plan view  1420  of the tripod  210  with the rear legs  240  and  250  with angular separation of 115°.  FIG. 14C  shows the elevation lateral view  1430  of the tripod  210 , with azimuth elevations of the fore leg  230  at 45° and of the rear legs  240  and  250  at 20° from ground level. Artisans will recognize that the configuration in which the starboard side incorporates the slide rail  950  constitutes a design decision, but is not limiting, such that reversal of the sides can be contemplated without departing from the scope of the invention. 
         [0051]      FIG. 15  shows a perspective assembly view  1500  of the right joint  340  for a third exemplary traverse bar  1510 . A right end  1520  on an extension  1530  from a primary segment  1540  of the traverse bar  1510  inserts into the first clevis bracket  910  at the left joint  350  forms a pivot assembly  1530 . The bracket  910  comprises an upper flange  1550  with corresponding through-hole  1560  and a lower flange  1570  with a complementary through-hole (not shown) to pin the right joint  340 . 
         [0052]      FIG. 16  shows a perspective exploded view  1600  of the left joint  350  for the first exemplary traverse bar  710 . The port slide rail  1010  attaches to the mezzanine flange  640  of the port leg  250  along a notch channel  1610 . The tang  1020  attaches to a threaded stud  1620  on the port slide rail  1010 . A flange  1630  secured by a pin  1640  limits travel of the rail  1010 . 
         [0053]      FIGS. 17A and 17B  show perspective assembly and exploded views  1700  of the right joint  340  for the third exemplary traverse bar  1510 . The clevis bracket  910  with flanges  1550  and  1570  attaches to the starboard rail  950  and pivotably secures the right end  1520  of the traverse bar  1510  thereto. The right end  1520  includes a terminus  1720  with a serrated cavity  1730  into which inserts a sprocket  1740  having an off-center orifice  1750 .  FIG. 18  shows a perspective view  1800  of the right end  1520  for the third exemplary traverse bar  1510 . Complementary holes  1810  on the terminus  1720  and the sprocket  1740  can be aligned to enable length adjustment of the traverse bar  1510 . 
         [0054]      FIGS. 19A and 19B  show plan and perspective assembly views  1900  of the right end assembly  1210  at right joint  340  for the second exemplary traverse bar  260  with the sprocket  1220 .  FIGS. 20A and 20B  show perspective exploded views  2000  of the right end  820  with the sprocket  1220  disposed beyond the corresponding cavity  850 . Outer splines  2010  along the rim of the sprocket  1220  correspond to tooth serrations  2020  through the cavity  850  into which the sprocket  1220  can be inserted at various angles to align the orifice  1230  to a desired configuration. 
         [0055]    Exemplary embodiments provide a curved traverse bar  260  that enables the machine gun (shown in application Ser. No. 14/752,707) to remain level while sweeping from one side to the other. With a conventional straight traverse bar  160 , the weapon traces a shallow elevation arc while rotating from side to side. View  200  shows the exemplary design with an exemplary curved traverse bar  260 . Due to the chaotic nature of a machine gun mount deployment under combat conditions, high tolerance parts should be minimized. The tripod  210  can loosen after repeated operation, causing joint connections to slacken. Both of these problems have been previously and conventionally mitigated by incorporating an adjustment mechanism to lengthen or shorten the conventional straight traverse bar  160 . On the conventional M122 tripod, an end screw was threaded into the traverse bar  160  for connection to the slider on the associated rear leg  140 . This screw could be tightened to shorten the traverse bar  160  or loosened to lengthen the traverse bar  160  and secured in place with a lock nut. 
         [0056]    This technique to adjust leg separation suffers deficiencies for an exemplary curved traverse bar  260 . Drilling a tapped hole for the end screw necessitates a straight bar. Because of the curvature in the exemplary traverse bar  260 , this technique cannot be so not easily accommodated. An early attempt at solving this problem with the first exemplary traverse bar  710  switched the adjustment mechanism to the slider with a fixed fork on the ends  720  and  730 . An evaluation test determined that this configuration was insufficiently robust to fulfill operational needs. The adjustable nut was not locked securely enough in place and was constantly battered back and forth during firing. This caused the structural material to yield in some sections. Also, opinions were expressed that the design was overly complicated. 
         [0057]    The view  900  of the traverse bar  260  shows the stop clamp  270 , while view  800  illustrates the traverse bar  260  in isolation. The traverse bar  260  features an elongated member  870  with graduations  810  marked thereon, terminating on the starboard leg  240  at the right joint  340  with the adjustable sprocket  1230  (or  1130 ), and on the port leg  250  at the left joint  350 . The right and left joints  340  and  350  disconnect and slide in their corresponding directions  360  along their respective starboard and port legs  240  and  250  to fold the exemplary tripod  210  in converging directions  370 . The right end  820  includes the serrated cavity  850  with annularly arranged teeth  2020 , sixteen being shown in this configuration, although this example is not limiting. These cavity teeth  2020  engage the splines  2010  of the sprocket  1220  to fix their relative positions. 
         [0058]    The left end  830  has a through-hole  860  that pivots on the left joint  350  of the port leg  250 . Both sides of the traverse bar  260  pivot and slide within the rear legs  240  and  250  along their respective joints  340  and  350 . Having the connection points slide and pivot enables a more compact shape when closed as well as shorter leg lengths than for a single pivot design. The traverse bar  260  has an exemplary straight-line length from the through-hole  860  of the left end  830  to the center of the sprocket  1120  (or  1220 ) of 12.297 inches. 
         [0059]    The sprocket  1120  can be produced separately from the traverse bar  260 , such as by extrusion and slicing perpendicular to its symmetry axis. The offset orifice  1130  enables its relative position in the sprocket  1120  to be altered by pushing the sprocket  1120  out of the cavity  850  turning the sprocket  1120 , and then reinserting that back into the cavity  850 , as shown in view  1300 . By angularly repositioning the cavity  850 , the tension between the legs  240  and  250  can be increased in response to fatigue wear loosening the original geometry, thereby necessitating adjustment. 
         [0060]    While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.