Abstract:
A shoe assembly for a micro-finishing machine for finishing a workpiece includes a C-frame structure adapted for nonrotatable mounting to the micro-finishing machine. The C-frame assembly includes a pair of slats and a replaceable insert secured nonrotatably to the C-frame assembly.

Description:
FIELD OF THE INVENTION 
     The present invention is related to micro-finishing tooling, and more particularly to a replaceable wear surface insert provided on such tooling for finishing cam lobes for internal combustion engine camshafts. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 4,993,191 discloses a tool for micro-finishing cam lobes and is incorporated herein by reference in its entirety. The cam tooling of the &#39;191 patent, typical of prior art finishing tools, includes articulating members to support the film for micro-finishing the cam lobes. As illustrated in FIG. 1 of the &#39;191 patent, rollers 44 are attached to a roller plate 40 by pins 46. The roller plate 40 is held by a support block 36 which is attached to the plates 40 by a pivot pin 42, thereby enabling the roller plates 40 to pivot about the pin 42. The rollers 44 are held by the roller plate 40 with the pins 46 enabling the rollers 44 to rotate. The rollers 44, as shown in FIG. 2 of the &#39;191 patent, support the finishing film 50. These pins and articulating connections are areas which have been discovered to present wear problems with this device. As these connections wear, the precision of the tool is compromised and therefore these worn components must be replaced. Such replacement is both time consuming and expensive, as these wear items are unique to these machines and must be manufactured specifically for this use. 
     U.S. Pat. No. 5,531,631 illustrates another micro-finishing tool useful for micro-finishing cylindrical workpieces such as crankshaft journals. This tool includes a pair of pivots, as illustrated in FIG. 12 at 94 and 96, about which the micro-finishing shoe 98 rotates. As discussed above, these pivots wear and therefore require replacement of the pins and of the tool hanger 116. This is, again, time consuming and expensive because these are custom parts for this particular machine. 
     U.S. Pat. No. 5,775,974 discloses a universal jaw attachment for a micro-finishing machine. As shown in FIG. 1, and described in column 2, prior art devices include shoes 32 which are permanently attached to jaw arms 14 and 16. Due to the permanent attachment and unique shape of these shoes, it is expensive and time consuming to service them upon wear, as in the other devices described above. FIGS. 2- 4  illustrate a two-piece shoe design utilizing shoe portions 118 permanently attached to jaw arms 121 and 122. Similar to that described above, these shoe portions 118 have a unique shape and are expensive to produce and time consuming to replace. The &#39;974 patent then describes a design to provide a universal shoe, as illustrated in FIGS. 6-10B. As shown in these figures, the universal shoe is complex, requiring several pieces and unique designs, thereby increasing the expense of these parts and the difficulty to service these upon wear. Further, the attachment includes a pinned attachment as best shown in FIGS. 10A and 10B, at 320 and 330. This, again, will produce wear at the pin connections, thereby requiring service of additional parts. 
     It would therefore be desirable to provide a simple design of a shoe for a camshaft finishing machine, the shoe having improved wear and an inexpensive and easily replaceable wear surface design. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a shoe assembly for a micro-finishing machine for finishing a workpiece. The shoe assembly includes a C-frame structure adapted for nonrotatable mounting to the micro-finishing machine and a pair of slats secured nonrotatably to the C-frame assembly. A replaceable insert is nonrotatably secured to the C-frame assembly. 
     By eliminating the rotatable connections, a machine according to the present invention avoids wear at the rotatable pinned connections. Furthermore, the replaceable insert is inexpensive and is easily replaced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a prior art micro-finishing machine. 
     FIG. 2 is a side view of an improved shoe assembly according to the present invention for use in a machine such as the one illustrated in FIG.  1 . 
     FIG. 3 is a partial side view of the shoe of FIG. 2 with one of the slats broken for viewing of the insert. 
     FIG. 4 illustrates a top view of the shoe assembly shown in FIG. 2 with the insert removed. 
     FIG. 5 is a partial sectional side view of the shoe of FIG. 2 taken along the line  5 — 5 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     As shown in prior art FIG. 1, a partial view of a micro-finishing machine  10  is shown. The machine  10  includes a pair of shoes  12 ,  13  attached thereto. The shoes  12 ,  13  are secured using fasteners  14  and  16 . A workpiece  18  is finished between the shoes  12  and  13 . The shoes  12  and  13  provide reinforcement for a tape  20  which micro-finishes the surface of the workpiece  18 , such as a crankshaft for an internal combustion engine. The shoes  12 ,  13 , as described with reference to first shoe  12 , include a pair of support members  22 ,  23  against which the tape  20  bears. The members  22 ,  23  have a pinned connection at  24 ,  26  to the shoes  12 ,  13 . The members  22 ,  23  thus rotate with respect to the shoes  12 ,  13  about the pins  24  and  26 . As described above with reference to the prior art in the Background section, the shoes  12 ,  13  wear at these pinned connections  24 ,  26 . 
     As shown in FIG. 2, an improved shoe  212  is provided for use in a machine similar to that illustrated in FIG.  1 . Shoe  212  may be used by replacing the shoes  12 ,  13  illustrated in FIG. 1 with improved a pair of shoes  212 . The improved shoe  212  includes a C-frame portion  213  having a pair of slats  215 ,  217  secured thereto using a pair of bolts  219 ,  221  each in a manner known to one skilled in the art. Alternatively, the slats  215 ,  217  could be formed or machined integrally, welded, or secured in a manner known to one skilled in the art to the C-frame  213 . A pin  230  is press-fit or welded to the slats  215 ,  217 . A replaceable insert  240 , shown in FIG. 2 but not illustrated in FIG. 3 for clarity, is press-fit over the pin  230  and secured to the slats  215 ,  217  by bearing against the slats  215 ,  217  at the underside of the insert  240  as illustrated in FIG.  5 . 
     FIG. 3 illustrates the insert  240  assembled to the pin  230  by breaking away part of the top slat  215 . As shown in FIG. 3, insert  240  includes a keyhole-shaped slot  242  providing for a snap-fit to the pin  230 . The slot  242  has a tapered first end to position the insert  240  over the pin  230 . The keyhole-shaped slot  242  reduces to a width of lesser dimension that the outside diameter of the pin  230  and opens thereafter into a substantially circular portion  243  for engagement with the pin  230 . Thus, the insert  240  may simply be installed by pressing onto the pin  230  and removed by pulling or prying the insert  240  away from the pin  230 . Thus, the insert  240  may be serviced quickly. This design may be injection molded or machined inexpensively. 
     The C-frame  213  is secured to the machine  10  using bolts  14 ,  16  installed through slots  214 ,  216  in the C-frame  213  in a manner known to one skilled in the art. 
     Preferably, the insert  240  is made from a glass-filled nylon material, thereby providing an inexpensive, durable wear surface. As shown in FIG. 2, the insert  240  has a substantially planar surface  241  against which the tape  220  bears for machining of the workpiece  218 . One skilled in the art appreciates that this planar surface  241  may be modified to be a curvilinear or wedge-shaped surface to accommodate various shapes as dictated by the workpiece  218  to be machined. The material is preferably a sand-filled polyurethane, or any other such material providing adequate wear properties, as known to one skilled in the art. As the material is not a critical part of this invention, further detail is not provided in the present disclosure. 
     In an alternative embodiment (not illustrated), the pin  230  is not present, and the insert  240  snaps into engagement with the slats  215 ,  217  in a known manner. In a further alternative embodiment (not shown), the insert  240  is screwed to the slats  215 ,  217  in a known manner. 
     While the invention has been shown and described in its preferred embodiments, it will be clear to those skilled in the art to which it pertains, that many changes and modifications may be made thereto without departing from the scope of the invention.