Two-piece drill bits

Abstract

Two-piece drill bits and methods of manufacturing same provide a preferably hexagonal shank, and a drill portion having a proximal end inserted into an axial hole in a distal end of the shank. In a preferred embodiment, at least part of the area adjacent the proximal end of the drill portion is knurled. Alternative embodiments have wings, polygons, tapers or other irregular shapes, or combinations of same. A variety of means may be employed to mechanically capture the drill portion in the shank.

claims:  
     
         1 . A two-piece drill bit, comprising a shank and a drill portion, said shank having a proximal end for mounting and a distal end having an axial hole for receiving a proximal end section of said drill portion, characterized by at least a portion of said proximal end section of said drill portion being knurled, said shank being compressed tightly against said proximal end section of said drill portion.  
     
     
         2 . A drill bit as in  claim 1 , further characterized by there being two said knurled portions, separated by an unknurled portion.  
     
     
         3 . A drill bit as in  claim 1 , further characterized by an unknurled portion adjacent said proximal end of said drill portion.  
     
     
         4 . A drill bit as in  claim 1 , characterized by said shank being compressed tightly against said proximal end section of said drill portion by a process selected from the group consisting of rolling, peening, roll-peening, pressing, and compression by differential heating and cooling.  
     
     
         5 . A drill bit as in  claim 1 , characterized by said axial hole being tapered, and said proximal end section of said drill portion being correspondingly tapered.  
     
     
         6 . A drill bit as in  claim 5 , further characterized by there being two said knurled portions, separated by an unknurled portion.  
     
     
         7 . A drill bit as in  claim 5 , further characterized by an unknurled portion adjacent said proximal end of said drill portion.  
     
     
         8 . A drill bit as in  claim 5 , characterized by said shank being compressed tightly against said proximal end section of said drill portion by a process selected from the group consisting of rolling, peening, roll-peening, pressing, and compression by differential heating and cooling.  
     
     
         9 . A drill bit as in  claim 1 , characterized by said shank having a proximal portion having one cross-sectional dimension, and a distal portion having a larger cross-sectional dimension, whereby said distal portion may accommodate drill portions of a larger diameter than if said distal portion was of the same cross-sectional dimension as said proximal portion.  
     
     
         10 . A two-piece drill bit, comprising a shank and a drill portion, said shank having a proximal end for mounting and a distal end having an axial hole for receiving a proximal end section of said drill portion, characterized by at least a portion of said proximal end section of said drill portion having an irregular cross-section, said shank being compressed tightly against said proximal end section of said drill portion.  
     
     
         11 . A drill bit as in  claim 10 , wherein said irregular cross-section is selected from the group consisting of wings extending radially outwardly, barbs extending radially outwardly, and a polygon.  
     
     
         12 . A drill bit as in  claim 11 , characterized by said shank being compressed tightly against said proximal end section of said drill portion by a process selected from the group consisting of rolling, peening, roll-peening, pressing, and compression by differential heating and cooling.  
     
     
         13 . A two-piece drill bit, comprising a shank and a drill portion, said shank having a proximal end for mounting and a distal end having an axial hole for receiving a proximal end section of said drill portion, characterized by said axial hole being tapered, and said drill portion having a correspondingly tapered proximal end, said shank being compressed tightly against said proximal end section of said drill portion.  
     
     
         14 . A drill bit as in  claim 13 , further characterized by at least a portion of said proximal end section of said drill portion being knurled.  
     
     
         15 . A method of manufacturing a two-piece drill bit, said two-piece drill bit comprising a shank and a drill portion, said shank having a proximal end for mounting and a distal end having an axial hole for receiving a proximal end section of said drill portion, said method comprising the steps of: 
 forming a knurled portion on at least a portion of said proximal end section of said drill portion;    providing shanks of a suitable length;    drilling an axial hole at a distal end of said shank; and    inserting said proximal end section of said drill portion into said axial hole.    
     
     
         16 . A method as in  claim 15 , comprising the further step of mechanically deforming at least a portion of said shank to symmetrically compress said shank onto said drill portion after said insertion of said proximal end section of said drill portion into said axial hole.  
     
     
         17 . A method as in  claim 15 , wherein said axial hole and said proximal end section of said drill portion are correspondingly tapered.  
     
     
         18 . A method as in  claim 17 , comprising the further step of mechanically deforming at least a portion of said shank to symmetrically compress said shank onto said drill portion after said insertion of said proximal end section of said drill portion into said axial hole.