Down-the-hole hammer

Abstract

The present invention relates to a down-the-hole hammer comprising an external cylindrical outer wear sleeve (), a sliding piston () mounted for reciprocating movement within the outer wear sleeve to strike a percussion bit () of a drill bit assembly located at the forward end of the outer wear sleeve. The drill bit assembly comprises a percussion bit having a head portion formed with an axially extending stub shank (); axially extending splines () on the stub shank slideably engageable with complementary splines () formed on a drive chuck () whereby rotational drive from the chuck may be transmitted to the stub shank; a bit retaining ring () adapted for engagement with a retaining shoulder () on the stub shank to retain the stub shank in the drill bit assembly; and engagement means on the chuck adapted for connecting the chuck to a drive means of the fluid-operated percussion drill tool; the bit retaining ring comprises a shoulder () for engagement with an upper end of the chuck to hold the retaining ring in place in the assembly. The assembly further comprises a bushing () arranged above the chuck. An upper portion of the bushing has an internal diameter (B) dimensioned to provide a sealing fit with the piston nose (). The bit retaining ring or the lower portion of the bushing has an internal diameter (E) dimensioned to provide a close sliding fit with the outer diameter of the retaining shoulder () on the stub shank ().