Drill bit assembly for fluid-operated percussion drill tools

A down-the-hole hammer comprising:

• an external cylindrical outer wear sleeve, and
• 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, wherein the drill bit assembly comprises:
• the 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;
• bit retaining means adapted for engagement with complementary retaining means 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;
• wherein the bit retaining means comprises a bit retaining ring, and the complementary retaining means comprises a retaining shoulder on the stub shank, wherein the bit retaining ring is arranged to engage the retaining shoulder to retain the stub shank in the drill bit assembly;
• wherein the bit retaining ring further comprises a shoulder for engagement with an upper end of the chuck, wherein the shoulder is an outward taper arranged to engage with a counterbore in the chuck to hold the bit retaining ring in place in the assembly;
• and
• wherein a portion of the bit retaining ring adapted to engage the retaining shoulder to retain the stub shank in the drill bit assembly is disposed within the chuck.