Abstract:
A blade or punch assembly for double-ended nibbler tools which affords easier removal by in part providing a blade having central portions of a single diameter equal to or slightly less than the composite bore through which it is adapted to extend.

Description:
This application is a division of U.S. patent application Ser. No. 10/757,943 filed Jan. 15, 2004 now U.S. Pat. No. 7,047,613. 
   Applicant claims the benefit of U.S. Provisional Patent Application No. 60/440,931 filed Jan. 17, 2003. 

   BACKGROUND OF THE INVENTION 
   This invention relates to nibbling tools and more specifically to nibbling tools that incorporate a double-headed structure such that opposed die cutting ends can be alternatively utilized by the operator so that when the blade of one end becomes dull the other cutting end can be utilized simply by removing a handle covering or grip provided over one end to expose the alternate die cutting end and then utilizing the handle to cover the other cutting die end. Such double-ended tools can utilize either separate blades or punches or a single blade or punch. The present invention is directed to those tools utilizing a single punch. The handle is provided to enable the operator to grasp and manipulate the tool. 
   Nibbling tools have been available in various forms for many years and include those set forth in UK Patent No. 1,485,795 published Sep. 14, 1977; U.S. Pat. No. 4,489,492 issued Dec. 25, 1984; U.S. Pat. No. 4,748,744 issued Jun. 7, 1988 and U.S. Pat. No. 4,158,913 issued Jun. 26, 1979. 
   All of the above-noted patents disclose a nibbler tool that includes a single die cutting head and a punch or blade that reciprocates with respect to the die. The die has an entry area or slot for receipt of a sheet of material such as thin sheet metal and is provided with a cutting surface that cooperates with the punch or blade. During operation, the punch or blade reciprocates in a linear motion and cooperates with the die to bite or nibble a small crescent-shaped piece of material from the sheet with each punch stroke. As the operator&#39;s hands guide the tool, the nibbler tool cuts a slot in the desired direction. 
   More recently, nibbler tools incorporating a double-headed die structure have been introduced as above indicated.  FIGS. 1 and 2  of the present drawings show the essential construction of one of such devices and in particular shows the construction of the reciprocating biter blade or punch housed within the structure itself. Although a decided improvement over single head nibbler tools, these double-headed nibble tools required considerable disassembly to install a new operating cutting punch or blade. 
   Accordingly, it is the object of the present invention to provide such double-headed nibbling tool structures with an improved blade assembly such that the blade can be easily removed with minimal disassembly and without requiring removal of either of the die heads or causing misalignment of the blade location block during such procedure. These and other objects of the present invention are accomplished by providing an elongated punch or blade having an extensive central portion of a uniform diameter that is equal to or slightly less than the diameter of the longitudinally oriented shaft or bore in which the blade is adapted to be received in the composite structure of the device. In this way, the replacement blade can be utilized to force the old and presumably dull blade out of the longitudinal bore while still maintaining contact with the blade location and drive block at all times such that misalignment thereof cannot occur and additionally afford a simple removal/installation procedure in the intended manner. 
   Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings. 

   
     DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
       FIG. 1  shows a cross-sectional view of a prior art double-ended nibbler tool; 
       FIG. 2  shows an enlarged section of the tool of  FIG. 1  and in particular shows the shape of the removable blade and the manner in which its central portion is enlarged; 
       FIG. 3  is cross-sectional view of the improved nibbler tool blade assembly of the present invention; 
       FIG. 4  is an enlarged cross-sectional view of  FIG. 3 ; 
       FIG. 5  is an elevational view of the new blade structure itself; and 
       FIG. 6  is a series of three progressive views showing the manner in which the old used blade in the present invention is removed by being pushed outwardly of its operational bore by the new blade without interfering with the blade location block. 
   

   DESCRIPTION OF THE INVENTION 
   Turning now to the drawings and particularly to  FIGS. 1 and 2 , the nibbler  10  shown therein includes a body  12  of generally cylindrical shape and including an open bore  14  at the top  16  thereof which part forms an internal cavity  18 . A drive mechanism  20  is located in the cavity and is utilized to transfer rotary movement from a drive shaft  22  to reciprocating longitudinal movement of a blade connector. The shaft extends through the base  24  of the body  12  and connected to the drive mechanism at one end thereof and a source of rotary motion such as a rotary drill (not shown) at the other end thereof. The drive mechanism is, in turn, connected to a blade location block  25  which includes a longitudinally extending body  26  having a longitudinal bore  28  therethrough adapted to receive and removably connect the nibbler blade  30  thereto. The drive mechanism may be of any known appropriate structure and of itself forms no part of the present invention; however, appropriate structures are shown in the prior art patents set forth above, e.g., U.S. Pat. No. 4,489,492 to Diggins which is herewith incorporated into the present specification. 
   A setscrew  32  is adapted to be threaded into an upper bore  34  in the blade location block and is provided with a conically-shaped forward end  36  that extends into a depression  38  centrally formed in the blade  30 . A lock  40  in the form of a nut having an internal threaded bore that engages both the setscrew and the top surface of the blade block is provided to assure continual fixed engagement of the blade location block to the blade. End cap  42  is provided to close the opening of the body  12 . Normally, a spring clip  43  is utilized to hold the end cap in position, but other means can be utilized. 
   A pair of aligned bores  48  extend through opposed sides of the body  12  in alignment with the blade location block bore but each of far greater diameter to respectively receive an inner forward cylindrically-shaped end  50  of each of the dies  52 . The dies include a central bore  54  to receive the blade—each bore being aligned with each other such that the blade may reciprocate upon drive shaft movement longitudinally within the compositely formed structure and operate to cut sheet material as it is fed into the receiving slot  58  of each die by the forward movement of the device vis-à-vis the sheet as is known in the art. 
   The central portion of such blade is of an enlarged diameter and, in effect, forms a shoulder portion  60  at each end thereof which is adapted to abut against an inwardly extending shelf provided in each die. In order for the blade to be removed in such prior art structures each die head has to be removed from the body by removing each respective setscrew  64  which retains such dies within the body and then the end cap locking bolt and setscrew removed or, at least, loosened such that the setscrew no longer engages the blade detent. Thereafter, the old blade may then be removed. Thereafter, a replacement blade may be installed by inserting one end thereof into one of the opposed bores  48  of the body and attempting to thread such through the bore  28  of the blade location block  25 . Sometimes this threading action requires extensive manipulation since the position of the blade block  25  and thus the orientation of the bore  26  thereof can be shifted upon movement of the blade block once the old punch is removed. Once the threading of the punch into the block  25  has been achieved, the opposite die ends are mounted over the opposite ends of the punch and then placed into their receiving bores and clamped into place by setscrews. 
   The structure of the present invention eliminates such complex and sometimes frustrating blade or punch removal described in the preceding paragraphs above by providing a blade structure  70  which is of a single continual central diameter and fits within a composite receiving bore within the overall body structure that is equal to or slightly greater than the blade diameter. Thus, the thicker central diameter of prior art punches is eliminated as is the shoulder or stop present in the die head central bore  54 . These changes enable the replacement blade to pass through the composite bore from one end to the other without obstruction, e.g., at shoulders or stops  55 . In this way only the end cap need be removed from the body, the locking bolt either removed or loosened to the extent that the setscrew is no longer engaged with the blade detent and then the new blade positioned at either end to engage the old blade and then pushed longitudinally to force the old blade progressively through the composite bore out the other end thereof until the new blade takes its correct position with its detent engaged centrally of the blade location block. Such action, especially brought out in  FIG. 6 , enables the new blade and old blade to compositely maintain the desired blade location block orientation since at all times either the old blade or the new blade is positioned in the bore  26  of such block  25  so that misalignment cannot occur. When the old blade has been completely removed from the opposite die end, the setscrew is simply screwed into engagement with the blade detent, the lock bolt tightened thereon and the end cap reinstalled—a relatively simple procedure which not only ensures the maintenance of the blade locator block but also eliminates the necessity of removing both of the die ends as in the prior art devices. 
   While there is shown and described herein certain specific is structure embodying this invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.