Stepped punch

Abstract

A punch for forming a punched opening in a metal sheet having an elongated body with a first and second spaced apart ends. The first end is adapted to be held by a machine which, when activated, axially drives the body. The second end of the body includes an annular surface corresponding in shape and size to the punched opening as well as an extension which protrudes outwardly from and is surrounded by the annular surface. The extension has a length greater than the thickness of the sheet metal so that, as the punch is driven through the sheet metal, the extension forms a hole in the sheet metal smaller than the opening and thereafter the annular surface forms the opening of the desired size in the metal sheet.

I claim: 
     
         1 . A punch for forming a punched opening in a metal sheet comprising:
 an elongated body having a first and a second spaced ends, said first end adapted to be held by a machine which, when activated, axially drives the body,   said body having a punch section axially spaced from said second end of said body, said punch section terminating in an annular surface corresponding in shape and size to the punched opening, and   an extension which extends axially outwardly from and is surrounded by said annular surface, said extension terminating at said second end of said body,   wherein said extension has a length greater than a thickness of the metal sheet so that, as the punch is driven through the metal sheet, said extension forms a hole in the metal sheet smaller than the opening and thereafter said annular surface forms the opening in the metal sheet.   
     
     
         2 . The punch as defined in  claim 1  wherein said punch is formed from hard metal. 
     
     
         3 . The punch as defined in  claim 1  and comprising a chamfer extending around a junction between said annular surface and said extension. 
     
     
         4 . The punch as defined in  claim 3  wherein said chamfer is formed on a radius. 
     
     
         5 . The punch as defined in  claim 1  wherein said body is a one piece construction. 
     
     
         6 . The punch as defined in  claim 1  wherein a free end of said extension lies in a plane perpendicular to said predetermined direction. 
     
     
         7 . The punch as defined in  claim 1  wherein said annular surface lies in a plane perpendicular to said predetermined direction. 
     
     
         8 . The punch as defined in  claim 1  wherein said extension is circular in cross-sectional shape. 
     
     
         9 . The punch as defined in  claim 1  wherein both said annular surface and said extension are circular in cross-sectional shape and wherein said extension has a diameter greater than sixty percent of the diameter of said annular surface.