Drill bit assembly for reverse circulation hammer

A drill bit assembly for a reverse circulation down-the-hole hammer, comprising:

• a percussion bit having an axially extending shank and a head portion with a cutting face at a forward end thereof;
• engagement means on the axially extending shank for engagement with complementary engagement means on a drive chuck whereby rotational drive from the drive chuck may be transmitted to the percussion bit;
• and
• connection means on the drive chuck adapted for connecting the drive chuck to a drive means of the down-the-hole hammer;
• wherein the percussion bit comprises:
• a central bore in fluid communication with the cutting face of the bit for returning a sample of drilled cuttings to the surface,
• a first plurality of flushing grooves in an outer surface of the head portion of the bit, configured to deliver a supply of flushing medium to the cutting face of the bit;
• and
• a second plurality of flushing grooves in the outer surface of the head portion of the bit, configured to deliver a supply of the flushing medium to the central bore.