Percussive drill bit provided with an improved chuck assembly

Abstract

The invention provides a drill bit for a down-the-hole drill hammer. The bit has a head at its forward end with a shank extending from the head. The shank is screw threaded along its length. A reciprocating chuck is provided as a sleeve with internal screw threads corresponding to those of the shank. The shank is releasably secured in the chuck with the rear end of the shank providing a striking face. An arrangement of external splines on the chuck, and a retaining shoulder at its rear end, provide for the required guided movement of the chuck within a drill hammer wear sleeve. The bit is simple to machine with screw threads replacing the usual splines and other structural features ordinarily required on this component. These features are instead provided on the chuck and in the wear sleeve.

1 . A drill bit for a down-the-hole drill hammer comprising a head with a shank adapted to be releasably secured in a reciprocating chuck. 
     
     
         2 . A bit as claimed in  claim 1  in which the rear end of the shank provides a striking face. 
     
     
         3 . A bit as claimed in  claim 1  in which the shank is screw threaded along its length. 
     
     
         4 . A bit as claimed in  claim 1  in which the chuck is externally splined. 
     
     
         5 . A bit as claimed in  claim 4 , in which the chuck has an outwardly extending shoulder at or near its rear end.