Abstract:
A one-piece stripper retainer for plastic cup shaped strippers with a universal snap-in design that can be used with both older style and newer style punch retainers. The stripper retainer incorporates an anti-rotation heel with a snug fit around a portion of the punch retainer body and clamps to the punch itself. In a second version, the stripper retainer also clamps to the punch itself but lacks the heel. In a third version, the stripper retainer bolts to the punch retainer with a separate threaded screw. In all three versions, the plastic stripper is locked in place by the snap-in feature without any additional clamping force.

Description:
This application claims the benefit of provisional patent application No. 60/663,695 filed Mar. 21, 2005. 

   BACKGROUND OF THE INVENTION 
   The field of the invention pertains to punches and dies for forming holes and depressions in metals. In particular, the invention pertains to devices and accessories for preventing work pieces from adhering to punches during high-speed high production manufacturing. 
   Examples of modern punch retainers are shown in applicant&#39;s previous U.S. Pat. Nos. 5,357,835, 5,410,932 and Des. 351,395. Views of these punch retainers are also shown in  FIGS. 1 ,  2 ,  8  and  9 . Modern punches for certain applications utilize a polyurethane cup that fits over the punch and is attached to the punch retainer by a two-piece metal stripper retainer. The two-piece stripper retainer was developed to provide adequate axial support for the cup. Although inexpensively stamped from sheet steel, the two-piece stripper retainer does not rigidly and accurately retain the polyurethane cup to the punch retainer to the degree desired. In addition, the two-piece stripper retainer will not fit the industries&#39; new smaller footprint ball-lock punch retainer for round shaped punches. 
   SUMMARY OF THE INVENTION 
   The new one-piece stripper retainer is a replacement for the older style two-piece stamped stripper retainer. The new style incorporates a unique snap-in design and can be used with both older style and newer style punch retainers. The new unit, being machined rather than stamped, is more precise and more accurately retains the urethane stripper, promoting improved life. The one-piece design simplifies the use of this stripper retainer by eliminating pieces that can get lost and provides for easier assembly by consolidating parts. In use, the urethane strippers grow or mushroom larger at their working end. Because the stripper has a head on one end and is deformed larger at the opposite end, the stripper is trapped. This makes it difficult or impossible to remove. Normal practice requires that the urethane stripper be cut in half or the stripper and retainer are thrown away. The new style eliminates this problem because exiting the retainer is accomplished by moving the urethane sideways out of the retainer, thus missing the interference caused by the mushroomed working end. The snap-in feature eliminates the need for any additional clamping force. The new stripper retainer in the first version incorporates an anti-rotation heel and snug fit around a portion of the punch retainer body that retains the punch and clamps to the punch itself. In a second version, the new stripper retainer also clamps to the punch itself but lacks the heel, and in a third version bolts to the punch retainer itself. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a prior art punch retainer; 
       FIG. 2  is a bottom plan view of the prior art punch retainer of  FIG. 1 ; 
       FIG. 3  is a top plan view of the upper piece of a prior art two-piece stripper retainer; 
       FIG. 4  is a top plan view of the lower piece of a prior art two-piece stripper retainer; 
       FIG. 5  is an exploded side view of a prior art stripper being attached to a retainer by a prior art two-piece stripper retainer; 
       FIG. 6  is the assembled side view of the prior art device of  FIG. 5 ; 
       FIG. 7  is a top plan view of the prior art device of  FIG. 6 ; 
       FIG. 8  is a top plan view of a prior art mini punch retainer; 
       FIG. 9  is a bottom plan view of the prior art mini punch retainer of  FIG. 8 ; 
       FIG. 10  is a top plan view of the first version of the new one-piece stripper retainer; 
       FIG. 11  is a bottom plan view of the stripper retainer of  FIG. 10 ; 
       FIG. 12  is a side elevation of the stripper retainer of  FIG. 10 ; 
       FIG. 13  is an exploded side view of a stripper being attached to a mini retainer by the new one-piece stripper retainer of  FIG. 10 ; 
       FIG. 14  is the assembled side view of  FIG. 13 ; 
       FIG. 15  is a top plan view of  FIG. 14 ; 
       FIG. 16  is a top plan view of the second version of the new one-piece stripper retainer; 
       FIG. 17  is a side elevation and nose view of the one-piece stripper retainer of  FIG. 16 ; 
       FIG. 18  is a top plan view of the third version of the new one-piece stripper retainer; and 
       FIG. 19  is a side cross section of the stripper retainer of  FIG. 18 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Illustrated in  FIGS. 1 and 2  is the top  10  and bottom  12  of a prior art punch retainer  14 . The punch retainer  14  includes counter-bored bolt holes  16  and a ball-lock punch retention hole  18 . In addition, there are threaded holes  20  and  22 . The prior art two-piece stripper retainer  24  in  FIGS. 3 and 4  comprises an upper piece  26  having an oblong hole  28  and a circular hole  30  that is counter-bored  32  from the underside. The lower piece  34  comprises and oblong hole  36  and a circular hole  38  sized to fit over a punch P (a portion of the punch P is shown in  FIG. 6 ). 
   As shown in  FIGS. 5 ,  6  and  7 , the upper piece  26  and lower piece  34  are assembled to the stripper cup  40  with the cup flange  42  fitting in the counter-bore  32  and the cup extending upwardly through hole  30  of the upper piece  26 . As shown in  FIG. 5 , the flange  42  extends outwardly from the stripper cup  40 . A screw  44  passes through the oblong holes  28  and  36  and screws into threaded hole  20  in the punch retainer  14 . As shown in  FIG. 6 , a punch  19  is retained in hole  18  and passes through hole  38  up into the stripper cup interior  46 . 
   Illustrated in  FIGS. 8 and 9  is a mini punch retainer  50 , top  52  and bottom  54 . Counter-bored bolt holes  56  and punch retention hole  58  are formed in retainer  50 , however, missing are the threaded holes  20  and  22  and rounded portion about hole  20  in retainer  14  above. As a result, the two-piece stripper retainer  24  above cannot be used with the mini punch retainer  50 . 
   Illustrated in  FIGS. 10 ,  11  and  12  is the first new version of a one-piece stripper retainer  60 . The new stripper retainer  60  has a bore hole  62  sized to just fit over a punch shaft extending from the retention hole  58  and a slot  64  extending from the bore hole to the exterior in the extended portion  66  of the retainer. The retainer  60  includes a hole that is drilled, counter-bored and threaded in the extended portion  66  for a screw  70  (shown in  FIG. 14 ) to tighten and loosen the retainer about the punch shaft (a portion of the punch  19  is shown in  FIG. 14 ). It is appreciated that  FIGS. 10 and 11  teach slot  64  extending through the stripper retainer  60  and being generally perpendicular to the rest of the retainer. As shown, the slot  64  divides the extended portion  66  of the retainer into two portions and the screw can move them towards each other. 
   As best shown in  FIGS. 10 and 12 , bore hole  62  is counter-bored  72  to the outside diameter of the stripper cup  40  and further undercut  74  to accommodate the stripper cup flange  42 . It is appreciated that the undercut  74  has a diameter greater than a diameter of the counter-bore  72 . Both the counter-bore  72  and the undercut  74  are slotted open at  76  and  78  respectively in a direction parallel to the axis of the hole  68  and screw  70 . The slot  78  width for the undercut  74  is at least equal to the diameter of the flange  42 , however, the slot  76  for the counter-bore  72  has a neck at  80  slightly less than the diameter of the stripper cup  40 . The slot  76  widens out from the neck  80  to the exterior of stripper retainer as best shown in  FIG. 10 . Thus, the stripper cup  40  “snaps in” and “snaps out” of the stripper retainer  60 . 
   Stripper retainer  60  includes a descending anti-rotation heel  82  shaped to snuggly fit the nose  84  of the mini punch retainer  50  with bore hole  62  axially aligned to punch retention hole  58  as best shown in  FIGS. 13 ,  14  and  15 . As shown in  FIG. 14 , with the punch already in the punch retention hole  58 , the stripper cup  40  is snapped into the stripper retainer  60  as indicated by arrow  86  and the stripper retainer placed on the punch retainer  50  with the punch passing through the bore hole  62  as indicated by arrow  88 . It is appreciated that  FIG. 12  teaches the stripper retainer  60  is a generally planar member with the bore hole  62 , counter-bore  72  and undercut  74  therewithin. In addition, the anti-rotation heel  82  extends from the generally planar member. 
   Illustrated in  FIGS. 16 and 17  is the second version of the new one-piece stripper retainer  90 . This stripper retainer  90  includes a bore hole  92 , a slot  94  and an extended portion  95  that has a drilled, counter-bored and threaded hole  96  as in the first version but lacks the heel. As above, the stripper retainer  90  is counter-bored at  98  and undercut  100  about the bore hole  92 , however the slotted openings for  102  and  104  for the counter-bore  98  and undercut  100  respectively are parallel and centered with the slot  94 . As above, the slot  102  necks down at  106  to provide the snap-in feature for the stripper cup  40 . 
   The second version of the new one-piece stripper retainer  90  clamps tightly to a punch extending from a punch retaining hole  58  as with the first version above. The second version  90 , however, is best suited for circular punches where rotational position about the axis of the bore hole  92  and punch retaining hole  58  is not critical. The second version  90  benefits from ease of installation and economy of manufacture. In addition, it is appreciated that  FIG. 17  teaches the stripper retainer  90  is a generally planar member with the bore hole  92 , counter-bore  98  and undercut  100  therewithin. 
   The third version of the new one-piece stripper retainer  110  is substantially oblong as shown in  FIGS. 18 and 19 . The third version  110  as above includes a bore hole  112 , a counter-bore  114  and an undercut  116 . The counter-bore  114  and undercut  116  are both slotted at  118  and  120  respectively, with the counter-bore slot  118  having a neck at  122  to provide the snap-in feature for the stripper cup  40  as explained above. 
   The third version  110  has an extended portion  124  with an oblong hole  126  spaced from the bore hole  112 . It is appreciated that  FIGS. 18 and 19  show a first end and a second end, for example the first end being proximate to the bore hole  112  and the second end proximate to the oblong hole  126 . The stripper retainer  110  is directed to use with the punch retainer  14  as shown in  FIGS. 1 and 2 . As above, the stripper cup  40  and flange  42  are snapped into the counter-bore  114  and undercut  116  and the stripper cup  40  is positioned over the punch which has been previously inserted in the punch retaining hole  18 . The screw  44  passes through the oblong hole  126  and is threaded into hole  20  to positively hold down the stripper retainer  110  and stripper cup  40  to the punch retainer  14 . In addition, it is appreciated that  FIG. 19  teaches the stripper retainer  110 , including the extended portion  124 , is a generally planar member with the bore hole  112 , counter-bore  114  and undercut  116  therewithin.