Overburden drilling apparatus having a down-the-hole hammer separatable from an outer casing/drill bit unit

Abstract

Overburden drilling equipment for drilling a hole includes a down-the-hole hammer formed by a cylinder and a piston reciprocating in the cylinder due to pressurized water being directed alternately to the upper and lower ends of the piston. Each downward stroke inflicts an impact blow upon an anvil portion of a drill bit extending upwardly within the lower portion of the cylinder. A drill chuck is mounted at a lower end of the cylinder to receive the drill bit. A generally cylindrical casing shoe is attached to a casing and is rotatably connected to the drill bit to be longitudinally advanced thereby during drilling operation. The drill chuck includes at least one key which defines the largest radius of the drill chuck. The casing includes a diametrically reduced portion which has at least one keyway therein. The key and the diametrically reduced portion retain the hammer longitudinally in relation to the drill bit.