Patent Publication Number: US-7587830-B2

Title: Knockout punch with pilot hole locator

Description:
CROSS-REFERENCE 
   This patent application is a divisional of U.S. patent application Ser. No. 10/085,730, filed Feb. 28, 2002, and entitled “Knockout Punch With Pilot Hole Locator”. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to an improved knockout punch which is used in conjunction with a punch driver to punch holes in sheet metal, for example, in the walls of electrical cabinets, aluminum, fiberglass and plastic. 
   Generally, when a hole is to be punched in an electrical cabinet, a small hole is first drilled in the wall of the electrical cabinet. A first end of a draw stud is threaded into a ram of a hydraulic punch driver. A second end of the draw stud is inserted through a punching die and then through the drilled hole, the draw stud having a circumference that is less than the circumference of the drilled hole. A knockout punch is threaded onto the second end of the draw stud on the opposite side of the electrical cabinet than is the punching die and the hydraulic punch driver. 
   An operator actuates a hand pump of the hydraulic punch driver. When the hand pump of the hydraulic punch driver is actuated, hydraulic fluid forces the ram to pull the draw stud. The draw stud, in turn, pulls the knockout punch through the electrical cabinet into the die such that the desired hole size is punched. 
   Knockout punches used in the prior art, such as standard round knockout punches, SLUG BUSTER® knockout punches sold by Greenlee Textron Inc., the assignee of the present invention, and those embodied in U.S. Pat. No. 4,353,164, which is owned by Greenlee Textron Inc., the assignee of the present invention, while proving very effective in the marketplace, suffer from a number of disadvantages. 
   One such disadvantage is that the prior art knockout punches do not provide means for locating the punch assembly in a pilot hole as the knockout punch and the die are drawn together by the draw stud to make a hole in the workpiece. Presently, an operator locates the punch assembly in a pilot hole by using “alignment marks” which can be difficult to see by the operator and may allow for error such that the hole to be created may not be properly positioned. 
   Another such disadvantage is that the prior art knockout punches typically have an elevated punching force at the beginning as the punch pierces the workpiece because the punch is working against a large length of the workpiece before the points of the punch fully pass through the workpiece. 
   Yet another such disadvantage is that the prior art knockout punches typically have an elevated punching force at the end of the punching cycle. The standard punch has a high punching force at the end of the punching cycle because it is shearing on four lines simultaneously and the angle of the punch faces reduces to zero at the end. The SLUG BUSTER® punch also has a high punching force at the end of the punching cycle because the long angled punch surfaces are “v” shaped, shearing on four lines simultaneously as the angle of the punch face reduces to zero toward the end of the punching cycle. 
   Another such disadvantage of the prior art knockout punches is that they do not have only planar surfaces which can be machined with standard cutting tools, such that custom formed tools or broaches are required to form the prior art knockout punches. 
   Thus, it is desirable to have a knockout punch which incorporates all of the advantages of the prior art knockout punches, but which overcomes the disadvantages of the prior art knockout punches, such as those identified above. The invention, as described herein, provides such a knockout punch. Other features and advantages of the knockout punch of the present invention will become apparent upon a reading of the attached specification in combination with a study of the drawings. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   A primary object of the invention is to provide a knockout punch which improves punch alignment over prior art devices, such as the current difficult to see alignment marks. 
   An object of the invention is to provide a knockout punch which automatically locates on a drilled pilot hole. 
   Another object of the invention is to provide a knockout punch which reduces the initial piercing force. 
   Yet another object of the invention is to provide a knockout punch which reduces the punching force at the end of the punching cycle. 
   An object of the invention is to provide a knockout punch which is lower in cost to manufacture than those found in the prior art. 
   Another object of the invention is to provide a knockout punch which requires a lower punching force to punch holes through a workpiece. 
   Yet another object of the invention is to provide a knockout punch which has a longer life than those found in the prior art. 
   Still another object of the invention is to provide a knockout punch which has only planar surfaces, allowing it to be machined with standard cutting tools. 
   Briefly, and in accordance with the foregoing, a novel knockout punch is provided. The knockout punch has a pilot hole locator provided therewith such that when the knockout punch and the die are drawn together by the draw stud to make a hole in a workpiece, for instance an electrical cabinet, the pilot hole locator on the knockout punch locates the punch assembly in the pilot hole. In one embodiment of the invention, the pilot hole locator is formed integrally with the knockout punch and extends from the knockout punch proximate to a bore in the knockout punch which is used to connect the knockout punch to the draw stud. In another embodiment of the invention, the pilot hole locator is provided as an insert which is connected to the knockout punch within a counterbore. In either embodiment, the knockout punch is also provided with a pair of piercing portions for piercing through the workpiece after the pilot hole locator has centered the punch assembly with the pilot hole and a pair of cutting portions for shearing the workpiece after the piercing portions have pierced the workpiece. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are described in detail hereinbelow. The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference numerals identify like elements in which: 
       FIG. 1  is a perspective view of a first embodiment of a punch which incorporates features of the present invention; 
       FIG. 2  is a side-elevational view of the punch of the first embodiment; 
       FIG. 3  is a side-elevational view of the punch of the first embodiment which is turned 90 degrees from the side-elevational view of the punch as illustrated in  FIG. 2 ; 
       FIG. 4  is a side-elevational view of the punch of the first embodiment which is turned 180 degrees from the side-elevational view of the punch as illustrated in  FIG. 2 ; 
       FIG. 5  is a top plan view of the punch of the first embodiment as illustrated in  FIG. 2 ; 
       FIG. 6  is a perspective view of a second embodiment of the punch which incorporates features of the present invention; 
       FIG. 7  is a perspective view of a third embodiment of the punch which incorporates features of the present invention; 
       FIG. 8  is a perspective view of a fourth embodiment of the punch which incorporates features of the present invention; 
       FIG. 9  is a side-elevational view of the punch of the fourth embodiment; 
       FIG. 10  is a side-elevational view of the punch of the fourth embodiment which is turned 90 degrees from the side-elevational view of the punch as illustrated in  FIG. 9 ; 
       FIG. 11  is a top plan view of the punch of the fourth embodiment as illustrated in  FIG. 8 ; 
       FIG. 12  is a cross-sectional view of the punch of the fourth embodiment taken along line  12 - 12  of  FIG. 11 ; and 
       FIG. 13  is a cross-sectional view of the punch of the fourth embodiment being pulled toward the workpiece by a drive member such that the insert member enters the pilot hole of the workpiece to center the punch with the pilot hole of the workpiece. 
   

   DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
   While this invention may be susceptible to embodiment in different forms, there is shown in the drawings and will be described herein in detail, specific embodiments with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated. 
   A knockout punch is provided. A first embodiment of the knockout punch  100  is illustrated in  FIGS. 1-5 . A second embodiment of the knockout punch  300  is illustrated in  FIG. 6 . A third embodiment of the knockout punch  500  is illustrated in  FIG. 7 . A fourth embodiment of the knockout punch  700  is illustrated in  FIGS. 8-13 . Like elements are denoted with like reference numerals with the reference numbers denoting the first embodiment being in the one and two hundreds, the reference numbers denoting the second embodiment being in the three and four hundreds, the reference numbers denoting the third embodiment being in the five and six hundreds, and the reference numbers denoting the fourth embodiment being in the seven and eight hundreds. 
   Each of the punches  100 ,  300 ,  500 ,  700  are useful for punching a hole through a workpiece  20 , such as 10-gauge, type  304  stainless steel, which is typically used to form electrical cabinets. The punches  100 ,  300 ,  500 ,  700  are used with a die  22  which is well known in the art as well as a draw stud  24  which is also well known in the art. A first end not shown of the draw stud  24  is typically threaded to a ram (not shown) of a punch driver (not shown). A second end  26  of the draw stud  24  is inserted through the die  22  and through a pilot hole  28  which is provided in the workpiece  20 , the draw stud  24  having a circumference that is less than the circumference of the pilot hole  28 . The punches  100 ,  300 ,  500 ,  700  are then attached to the second end  26  of the draw stud  24  on the opposite side of the workpiece  20  than is the die  22  and the hydraulic punch driver. 
   An operator actuates a hand pump of the hydraulic punch driver. When the hand pump of the hydraulic punch driver is actuated, hydraulic fluid forces the ram to pull the draw stud  24 . The draw stud  24 , in turn, pulls the punch  100 ,  300 ,  500 ,  700  through the electrical cabinet into the die  22  such that the desired hole size is punched. 
   Attention is now directed to the first embodiment of the punch  100  shown in  FIGS. 1-5 . The punch  100  includes a generally cylindrical punch body  102  and a punch face  108  having a passageway  104  extending axially therethrough. A wall  106  of the passageway  104  is typically threaded and threadably receives a threaded end of the draw stud in a conventional fashion. The working face  108  has a novel arrangement of inclined surfaces and associated cutting edges and surfaces for centering the punch  100 , draw stud and die, which will be referred to collectively as the punch assembly, with the pilot hole, punching through the workpiece, and splitting apart of a slug to be removed from the workpiece. 
   The working face  108  includes a pair of inclined planar surfaces  110 ,  112  on opposite sides of a line D, see  FIG. 5 , which corresponds to the diameter of the working face  108 . The inclined planar surfaces  110 ,  112  slope upwardly from the punch body  102  in opposite directions at an angle α. The inclined planar surfaces  110 ,  112  have outer circumferential or peripheral edges which form outer cutting edges  114 ,  116  around a large portion of the working face  108  periphery when viewed in the top plan shown in  FIG. 5 . 
   The inclined planar surface  110  has inner ends  118   a ,  118   b  parallel with and spaced from line D across the working face  108  in top plan view with inner edge  118   a  and inner edge  118   b  being on opposite sides of the passageway  104 . The inclined planar surface  112  has inner ends  120   a ,  120   b  parallel with and spaced from line D across the working face  108  in top plan view with inner edge  120   a  and inner edge  120   b  being on opposite sides of said passageway  104 . 
   The inclined planar surface  110  inclines at angle α from inner edge  118   a  to inner edge  118   b  such that inner edge  118   b  is positioned higher than the inner edge  118   a . The inclined planar surface  112  inclines at angle α from inner edge  120   b  to inner edge  120   a  such that inner edge  120   a  is positioned higher than the inner edge  120   b . ends  118   a ,  120   b  are positioned at the same height while inner ends  118   b ,  120   a  are positioned at the same height. 
   The working face  108  includes an extension member  122  between the inner ends  118   a ,  120   a  and the passageway  104 . Similarly, the working face  108  includes an extension member  124  between the inner ends  118   b ,  120   b  and the passageway  104 . 
   The extension member  122  has an outer peripheral surface  126 , an inner surface  128 , a first side surface  130  which extends vertically from the inner edge  118   a  between the outer peripheral surface  126  and the inner surface  128 , and a second side surface  132  which extends vertically from the inner edge  120   a  between the outer peripheral surface  126  and the inner surface  128 . 
   The outer peripheral surface  126  is defined by first and second outer peripheral edges  134 ,  136 . The first outer peripheral edge  134  extends vertically from an outer end of the inner edge  118   a  to a point  138  which is positioned at a height higher than both the inner edge  118   a  and the inner edge  120   a . The second outer peripheral edge  136  tapers downwardly from the point  138  to an outer end of the inner edge  120   a.    
   The inner surface  128  is defined by first, second and third inner edges  140 ,  142 ,  144 . The first inner edge  140  extends vertically from an inner end of the inner edge  118   a  to a first end of the second inner edge  142 . The third inner edge  144  extends vertically from an inner end of the inner edge  120   a  to a second end of the second inner edge  142 . The second inner edge  142  is positioned at a height higher than the point  138 , and is preferably positioned at a height of about 1/16 of an inch higher than the point  138 . The inner surface  128  is an extension of the wall  106  of the passageway  104  and, therefore, is arced as is the wall  106  of the passageway  104 . Thus, the second inner edge  142  is arced. 
   The extension member  122  has a first top surface  146  which extends horizontally from the second inner edge  142  toward the outer peripheral surface  126  to an outer edge  148 . The first top surface  146  is generally arced and, therefore, the outer edge  148  is also generally arced. The first top surface  146  further has a first side edge  150  and a second side edge  152 . The first side edge  150  is also an edge of the first side surface  130  while the second side edge  152  is also an edge of the second side surface  132 . 
   The extension member  122  has a second top surface  154  which tapers downwardly and outwardly toward the outer peripheral surface  126  from the outer edge  148  to an outer edge  156 . The second top surface  154  is generally arced and, therefore, the outer edge  156  is also generally arced. The second top surface  154  further has a first side edge  158  and a second side edge  160 . The first side edge  158  is also an edge of the first side surface  130  while the second side edge  160  is also an edge of the second side surface  132 . 
   The second top surface  154 , the first top surface  146  and the inner surface  128  combine to form a tapered projection  161  of the extension member  122 . 
   The extension member  122  has a third top surface  162  which extends horizontally from the outer edge  156  toward the outer peripheral surface  126  to an outer edge  164 . The outer edge  164  is generally arced. The third top surface  162  further has a first side edge  166  and a second side edge  168 . The first side edge  166  is also an edge of the first side surface  130  while the second side edge  168  is also an edge of the second side surface  132 . 
   The extension member  122  has a fourth top surface  170  which tapers downwardly and inwardly toward the inner surface  128  from the point  138  to the outer edge  164 . The fourth top surface  170  tapers downwardly at an angle β relative to an axial line L through the center of the passageway  104 . The fourth top surface  170  further has a first side edge  172  and a second side edge  174 . The first side edge  172  is also an edge of the first side surface  130 . 
   The extension member  122  has a fifth top surface  176  which tapers downwardly toward the inner edge  120   a  from the point  138  to an edge  178 . The edge  178  is also an edge of the second side surface  132 . The second side edge  174  and the second outer peripheral edge  136  are the other edges of the fifth top surface  176 . 
   The fourth top surface  170 , the fifth top surface  176 , the outer peripheral surface  126  and the point  138  combine to form a piercing portion  179  of the extension member  122 . 
   The extension member  124  has an outer peripheral surface  180 , an inner surface  182 , a first side surface  184  which extends vertically from the inner edge  120   b  between the outer peripheral surface  180  and the inner surface  182 , and a second side surface  186  which extends vertically from the inner edge  118   b  between the outer peripheral surface  180  and the inner surface  182 . 
   The outer peripheral surface  180  is defined by first and second outer peripheral edges  188 ,  190 . The first outer peripheral edge  188  extends vertically from an outer end of the inner edge  120   b  to a point  192  which is positioned at a height higher than both the inner edge  120   b  and the inner edge  118   b . The second outer peripheral edge  190  tapers downwardly from the point  192  to an outer end of the inner edge  118   b.    
   The inner surface  182  is defined by first, second and third inner edges  194 ,  196 ,  198 . The first inner edge  194  extends vertically from an inner end of the inner edge  120   b  to a first end of the second inner edge  196 . The third inner edge  198  extends vertically from an inner end of the inner edge  118   b  to a second end of the second inner edge  196 . The second inner edge  196  is positioned at a height higher than the point  192 , and is preferably positioned at a height of about 1/16 of an inch higher than the point  192 . The inner surface  182  is an extension of the wall  106  of the passageway  104  and, therefore, is arced as is the wall  106  of the passageway  104 . Thus, the second inner edge  196  is arced. 
   The extension member  124  has a first top surface  200  which extends horizontally from the second inner edge  196  toward the outer peripheral surface  180  to an outer edge  202 . The first top surface  200  is generally arced and, therefore, the outer edge  202  is also generally arced. The first top surface  200  further has a first side edge  204  and a second side edge  206 . The first side edge  204  is also an edge of the first side surface  184  while the second side edge  206  is also an edge of the second side surface  186 . 
   The extension member  124  has a second top surface  208  which tapers downwardly and outwardly toward the outer peripheral surface  180  from the outer edge  202  to an outer edge  210 . The second top surface  208  is generally arced and, therefore, the outer edge  210  is also generally arced. The second top surface  208  further has a first side edge  212  and a second side edge  214 . The first side edge  212  is also an edge of the first side surface  184  while the second side edge  214  is also an edge of the second side surface  186 . 
   The second top surface  208 , the first top surface  200  and the inner surface  182  combine to form a tapered projection  215  of the extension member  124 . 
   The extension member  124  has a third top surface  216  which extends horizontally from the outer edge  210  toward the outer peripheral surface  180  to an outer edge  218 . The outer edge  218  is generally arced. The third top surface  216  further has a first side edge  220  and a second side edge  222 . The first side edge  220  is also an edge of the first side surface  184  while the second side edge  222  is also an edge of the second side surface  186 . 
   The extension member  124  has a fourth top surface  224  which tapers downwardly and inwardly toward the inner surface  182  from the point  192  to the outer edge  218 . The fourth top surface  224  tapers downwardly at an angle β relative to the axial line L. The fourth top surface  224  further has a first side edge  226  and a second side edge  228 . The first side edge  226  is also an edge of the first side surface  184 . 
   The extension member  124  has a fifth top surface  230  which tapers downwardly toward the inner edge  118   b  from the point  192  to an edge  232 . The edge  232  is also an edge of the second side surface  186 . The second side edge  228  and the second outer peripheral edge  190  are the other edges of the fifth top surface  230 . 
   The fourth top surface  224 , the fifth top surface  230 , the outer peripheral surface  180  and the point  192  combine to form a piercing portion  233  of the extension member  224 . 
   The extension members  122 ,  124  are preferably identical to one another, but are oppositely arranged. 
   Operation of the punch  100  will now be discussed. As explained above, an operator threads a first end of a draw stud to a ram of a punch driver. A second end of the draw stud is inserted through a die and through a pilot hole which is provided in a workpiece, the draw stud having a circumference which is less than the circumference of the pilot hole. The punch  100  is then attached to the second end of the draw stud on the opposite side of the workpiece than is the die and the hydraulic punch driver. The punch  100  is attached to the draw stud by threading the second end of the draw stud into the passageway  104  of the punch  100  which has a threaded wall  106 . 
   In the preferred embodiment, the operator turns the punch  100  onto the draw stud until the punch  100  and the die are tight on the workpiece and the tapered projections  161 ,  215 , which are positioned adjacent to the draw stud, enter the pilot hole and cause the punch  100 , the draw stud and die to center on the pilot hole. The operator could also actuate a hydraulic punch driver until the punch  100  and the die are tight on the workpiece. 
   After the tapered projections  161 ,  215  enter the pilot hole to center the punch  100 , the operator actuates a hand pump of the hydraulic punch driver such that hydraulic fluid forces the ram to pull the draw stud, which in turn pulls the punch  100 , such that the points  138 ,  192  pierce through the workpiece and the workpiece is cut along the fourth and fifth top surfaces  170 ,  176 ;  224 ,  230 . 
   After the workpiece is cut along the fourth and fifth top surfaces  170 ,  176 ;  224 ,  230 , and the points  138 ,  192  have fully passed through the workpiece, the inclined planar surfaces  110 ,  112  begin shearing the workpiece to create a hole having a diameter equivalent to the diameter of the working face  108 , which is larger than a diameter of the pilot hole. As the points  138 ,  192  pierce through the workpiece, lateral cutting or splitting of a slug (not shown) is initiated from a slug periphery (defined by the diameter of the working face  108 ) toward a slug center (defined by the pilot hole through the workpiece) before a significant part of the slug periphery is cut by the outer edges  114 ,  116  of the inclined planar surfaces  110 ,  112 . With further penetration, lateral splitting of the slug continues and preferably is substantially complete before the outer cutting edges  114 ,  116  begin cutting their portion of the slug periphery. The entire slug periphery is thus cut and the slug is split apart into two pieces for easy removal from the draw stud and the die. 
   The configuration of the punch  100 , in comparison to punches of the prior art, reduces the initial piercing force by reducing the area of contact between the punch  100  and the workpiece. The two points  138 ,  192  have steep tapers and are high enough that the points  138 ,  192  have fully passed through the workpiece before the inclined planar surfaces  110 ,  112  begin shearing the hole. In prior art punches, the punches work against a greater length of the workpiece before the points fully pass through the workpiece. 
   The configuration of the punch  100  also maintains a constant shearing angle throughout the punching cycle except for the points  138 ,  192  used to initially pierce the workpiece. Prior art punches typically have an elevated punching force at the end of the punching cycle. In one prior art punch, the punching force is high because the punch is shearing on four lines simultaneously and the angle of the punch face reduces to zero at the end of the punching cycle. In another prior art punch, the inclined planar surfaces of the punch are “v” shaped, shearing on four lines simultaneously as the angle of the punch face reduces to zero toward the end of the punching cycle. 
   The configuration of the punch  100  also is advantageous because the punch  100  has only planar surfaces which can be machined with standard cutting tools. Unlike prior art punches, no custom form tools or broaches are required. 
     FIG. 6  illustrates a second embodiment of the punch  300  where the angle β (not shown) is larger than the angle β as illustrated in  FIGS. 1-5  and  FIG. 7  illustrates a third embodiment of the punch  500  where the angle β (not shown) is larger than the angle β of the second embodiment of the punch  300 . Further discussion of the second and third embodiments of the punches  300 ,  500 , with the larger angles β will not be discussed herein as the remainder of the punches  300 ,  500  are identical to the punch  100  except with regard to dimensions. 
   Attention is now directed to the fourth embodiment of the punch  700  shown in  FIGS. 8-13 . The punch  700  includes a generally cylindrical punch body  702  and a working face  708  having a passageway  704  extending axially therethrough. A wall  705  of the passageway  704  is typically threaded and threadably receives a threaded end  26  of the draw stud  24  in conventional fashion. The working face  708  has an arrangement of inclined surfaces and associated cutting edges. An insert  840  extends from the working face  708  and is permanently fastened into a counterbore  709  of the passageway  704  and is used for centering the punch  700 , draw stud  24  and die  22  with the pilot hole  28  prior to the punch  700  punching through the workpiece  20 . 
   The working face  708  includes a pair of inclined planar surfaces  710 ,  712  on opposite sides of line D, which corresponds to the diameter of the working face  708 . The inclined planar surfaces  710 ,  712  are generally crescent-shaped such that outer circumferential edges  714 ,  716  of the inclined planar surfaces  710 ,  712  are convex while the inner edges  842 ,  844  thereof are concave. The outer circumferential or peripheral edges  714 ,  716  act as outer cutting edges  714 ,  716  around a large portion of the periphery of the working face  708  when viewed in the top plan shown in  FIG. 11 . The inclined planar surfaces  710 ,  712  slope upwardly from the outer cutting edges  714 ,  716  to the inner edges  842 ,  844  of the inclined planar surfaces  710 ,  712 . 
   The inclined planar surface  710  has a first end  846  and a second end  848 . The inclined planar surface  712  has a first end  850  and a second end  852 . The first and second ends  846 ,  848  of the inclined planar surface  710  are positioned at the same height as the first and second ends  850 ,  852  of the inclined planar surface  712 . The first and second ends  846 ,  850 ;  848 ,  852  of the inclined planar surfaces  710 ,  712  are positioned at a height which is higher than a middle portion  854 ,  856  of the inner edges  842 ,  844  of the inclined planar surfaces  710 ,  712 , which in turn, are positioned at a height which is higher than a middle portion  858 ,  860  of the outer edges  714 ,  716  of the inclined planar surfaces  710 ,  712 . The middle portion  854 ,  856  of the inner edges  842 ,  844  borders the wall  705  of the passageway  704  at the counterbore  709  thereof. 
   The first end  846  of the inclined planar surface  710  is connected to the second end  852  of the inclined planar surface  712  at a point  738 . The second end  848  of the inclined planar surface  710  is connected to the first end  850  of the inclined planar surface  712  at a point  792 . 
   The working face  708  further includes a pair of top surfaces  862 ,  864 . The top surface  862  extends from the point  738  to the wall  705  of the passageway  704  at the counterbore  709  such that the top surface  862  is bordered by the inner edge  842  of the inclined planar surface  710  from the point  738  to the middle portion  854  thereof, the inner edge  844  of the inclined planar surface  712  from the point  738  to the middle portion  856  thereof, and the wall  705  of the passageway  704  at the counterbore  709 . The top surface  864  extends from the point  792  to the wall  705  of the passageway  704  at the counterbore  709  such that the top surface  864  is bordered by the inner edge  842  of the inclined planar surface  710  from the point  792  to the middle portion  854  thereof, the inner edge  844  of the inclined planar surface  712  from the point  792  to the middle portion  856  thereof, and the wall  705  of the passageway  704  at the counterbore  709 . 
   The insert  840  is preferably cylindrical and has an aperture  866  therethrough. The insert  840  is capable of being permanently fastened into the counterbore  709  of the punch  700  by press fitting, welding, threading or bolting, or by any other suitable means. The insert  840  extends upwardly from the counterbore  709  to a top  868  thereof. The top  868  of the insert  840  is preferably positioned at a height of about 1/16 of an inch higher than the points  738 ,  792 . The top  868  of the insert  840  further has a chamfered edge  870  from an inner diameter ID of the insert  840  to an outer diameter OD of the insert  840 . The chamfered edge  870  preferably angles downwardly and outwardly at an angle between approximately 30 degrees and 45 degrees. The inner diameter ID of the insert  840  is preferably of the same diameter as the passageway  704  of the punch  700  such that the draw stud  24  can also be threaded into the aperture  842  of the insert  840  if required. 
   Operation of the punch  700  will now be discussed. As explained above, an operator threads a first end of a draw stud  24  to a ram of a punch driver. A second end  26  of the draw stud  24  is inserted through a die  22  and through a pilot hole  28  which is provided in a workpiece  20 , the draw stud  24  having a circumference which is less than the circumference of the pilot hole  28 . The punch  700  is then attached to the second end  26  of the draw stud  24  on the opposite side of the workpiece  20  than is the die  22  and the hydraulic punch driver, as best illustrated in  FIG. 13 . The punch  700  is attached to the draw stud  24  by threading the second end  26  of the draw stud  24  into the passageway  704  of the punch  700  which has a threaded wall, with the draw stud  24  extending through the insert  840 . 
   In the preferred embodiment, the operator turns the punch  700  onto the draw stud  24  until the punch  700  and die  22  are tight on the workpiece  20  and the chamfered edge  870  of the top  868  of the insert  840 , which is positioned adjacent to the draw stud  24 , enters the pilot hole  28  causes the punch  700 , the draw stud  24  and the die  22  to center on the pilot hole  28 , as illustrated in  FIG. 13 . The operator could also actuate a hydraulic punch driver until the punch  700  and the die  22  are tight on the workpiece  20 . 
   After the insert  840  enters the pilot hole  28  to center the punch  700 , the draw stud  24  and the die  22  on the pilot hole  28 , the operator actuates a hand pump of the hydraulic punch driver such that hydraulic fluid forces the rain to pull the draw stud  24 , which in turn pulls the punch  700  such that the points  738 ,  792  pierce through the workpiece  20 . The inclined planar surfaces  710 ,  712  begin shearing the workpiece  20  to create a hole having a diameter which is larger than a diameter of the pilot hole  28 . A slug is created from the workpiece  20  where the hole is formed and tire slug can be split depending on the configuration of the cutting surfaces. 
   The points  738 ,  792  piercing the workpiece  20  before the inclined planar surface  710 ,  712  shear the workpiece  20 , minimizes the required punching force. 
   In the fourth embodiment, the configuration of the cutting surfaces is not important to the embodiment as long as the cutting surfaces can create a hole having a diameter D, which is larger than a diameter of the pilot hole  28 .