You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to dragline excavating machines which have a main support center pin assembly. Dragline excavation machines are supported on a central stabilization tub during excavating. As such, stress is imparted thereto by the shear weight of the machine and the excavating movements required during use. Such large machines are movable from location to location by use of a walking mechanism that lifts the entire machine up and forward repeatedly imparting increased stress and wear to the center pin and support structure as well as during use in which lateral forces are encountered and the machine pivots on the center pin support structure. 
     2. Description of Prior Art 
     Prior art support tubs and center pin assemblies can be seen in the following U.S. Pat. Nos. 5,154,012, 5,154,013, 5,676,471. 
     In U.S. Pat. No. 5,154,012 a support tub for a dragline excavating machine is described with a circular tracking ring support and a lifting stool assembly with a center pin lifting pin threadably secured within a bearing support frame. 
     U.S. Pat. No. 5,154,013 is a support tub for a dragline directed to a lifting stool with lifting pivot pin. 
     U.S. Pat. No. 5,676,471 claims a dragline excavator with improved thrust bearing assemblies support upper structure. A center pin connects the upper structure to the lower structure of the support. A perimeter annular rail with rollers provide for rotation of the structure thereabout. 
     SUMMARY OF THE INVENTION 
     A center pin support bearing fitting assembly to pivotally support and maintain a dragline structure on a center support tub during excavating and selectively while moving using a walking mechanism. The center pin support has multiple bearing bore configuration by adding an additional bore bearing support at the center pin base spaced in relation to the primary support bores within the support bearing fitting assembly within the center support tub frame of the dragline. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a center pin support bearing fitting illustrating multiple bore support elements of the invention. 
         FIG. 2  is a cross-sectional view on lines  2 - 2  of  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the center support bearing assembly of the invention with a center pin positioned therewithin. 
         FIG. 4  is a cross-sectional view of a prior art center pin bearing bore assembly. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A dragline excavator center pin bearing support assembly  10  of the invention can be seen in  FIGS. 1 and 2  of the drawings. The dragline center pin support assembly  10  has an annular pivot pin housing  11  which is positioned within a dragline excavator tub (not shown). The housing  11  has an annular base plate  12  with an upstanding perimeter annular sidewall  13 . A top wall  14  extends from the sidewall  13  radially upwardly to a primary bearing fitting  15  in which a center pivot retention pin  16  extends as seen in  FIG. 3  of the drawings. 
     The primary bearing fitting  15  has a center bore  17  therethrough with an upper pin receiving opening at  17 A and a lower pin exit opening at  17 B. The bearing fitting  15  has an area of reduced internal bore dimension at  18  adjacent the lower exit bearing opening  17 B which will be described in greater detail hereinafter. 
     The bearing fitting  15  is positioned on and supported by an annular sleeve  19  with a horizontally extending stabilization frame plate  20  extending radially therefrom. The annular support sleeve  19  extends from and is supported by a raised central bearing platform  21  on the base plate  12  and is in vertical alignment with the hereinbefore described lower bore exit opening  17 B. 
     The annular support sleeve  19  has multiple power line access openings at  22  annularly spaced thereabout as best seen in  FIG. 1  of the drawings. The central bearing fitting  15  is preferably of a cast monolithic construction and defines two bearing guide engagement surfaces within the bore  17 . The first bearing guide surface within the bore  17  is its interior annular wall surface  23  extending from the upper pin receiving opening at  17 A. 
     A second bearing guide engagement surface  24  is defined by the hereinbefore described area of reduced interior bore diameter at  18 . 
     It will be evident from the above description that as illustrated best in  FIG. 3  of the drawings the center pivot retention pin  16  is engaged by the first bearing guide surface annular wall  23  therealong and the second bore guide engagement surface  24  adjacent thereto as noted. 
     Referring back now to  FIG. 1  of the drawings the raised central bearing platform  21  is of a solid monolithic construction and has a central annular center pin receiving recess  25  therewithin which defines a stabilization bearing pocket for the base of the center pivot retaining pin  16 . The center retaining pin  16  shown in this example is of a cast construction having an outer upper and lower bearing surfaces  26  and  27  respectively of different annular diameter. A bore at  28  extends longitudinally therethrough with at least one horizontally disposed opening at  29  extending through the lower surface  27 . 
     It will be evident from the above description that the geometry of the center pivot retaining pin  16  defines that the upper and lower bearing surface portions  26  and  27  are of different wall thicknesses induced thereby. The center pin  16  provides a pivot access and retention for the dragline (not shown) to prevent unintended lateral movement thereof as will be well understood within the art. The base of the center pivot retaining pin  16  is registerably received within the recess  25  of the bearing platform  21  which in combination with the hereinbefore described first and second bearing surfaces in the primary bearing fitting  15  reduces extraneous wear and increases the working life of the assembly. 
     Comparison to prior art designs which can be seen in  FIG. 4  of the drawings, prior art typically relies only on a center pin support assembly  30  having a prior art center pin  31  retained within a prior art center cast bearing fitting  32  defining two guide bearing surfaces  33  and  34  (bores) therewithin. The prior art pin  31  simply extends downwardly without any additional translateral support thus imparting additional wear and eventual failure to the limited prior art bearing surfaces of the central pin and support assembly  30 . 
     If will therefore be evident that the present invention by having a central stabilization pin receiving bearing pocket recess  25  within the base plate  21  increases the useful product life of the assembly. 
     It will thus be seen that a new and improved center pin support bearing and guide fixture has been illustrated and described and it will be apparent to those skilled in the art that various changes and modifications may be made thereto without departing from the spirit of the invention.

Summary:
A center pivot pin support bearing assembly to provide rotatable center restraint for a dragline excavator machine. Multiple center pin bearing support fittings imparts stabilization and additional bearing wear surfaces for increased pin useful service life before replacement. An axially center pin bore receiving fitting is provided for longitudinal spaced multiple support fits combination with a center pin receiving stabilization base and fit.