Abstract: An air lift system for large diameter borehole drilling is disclosed. The system is applicable in drilling operations where a vertical pilot hole is drilled below the point to which the borehole will later be enlarged and a slant hole is drilled obliquely to intersect the pilot hole near its nether position. During the drilling operation, the circulation system pumps drilling fluid down the annulus of the borehole to cool the cutterhead and to mix with the cuttings. The drilling fluid carrying the cuttings then moves down the pilot hole and up through the slant hole. A plenum is located in the slant hole to assist in the lifting of the drilling fluid. The plenum includes a tapered transition pipe, a tapered discharge horn, and an air diffusion ring located at the throat of the discharge horn. The diffusion ring is utilized to inject outside air into the drilling fluid passing therethrough.

Abstract: A large diameter drill bit having a plurality of rolling cutters is provided with permanent magnets mounted on flexible flaps to collect magnetic debris on the bottom of a drill hole. A flap carrying a permanent magnet is mounted adjacent each cutter, or flaps carrying magnets are formed in a radially extending row to sweep the bottom of the hole as the bit rotates. In another form, magnets are included in wheels which roll on the bottom of the hole to collect the magnetic debris.

Abstract: A drill bit is disclosed for drilling large diameter shafts. The drill bit comprises a main bit body having a plurality of rolling cutters rotatively mounted thereon. The cutters function to contact and disintegrate the earth formations at the bottom of the shaft thereby creating rock chips or cuttings. Water or drilling mud is pumped down the shaft and across the face of the main bit body for cooling the drill bit and for flushing the chips away from the shaft bottom. An auxiliary flow enhancer is attached beneath the main bit body for increasing the radial flow velocity of the drilling mud across the face of the bit body in order to remove the chips more efficaciously. The flow enhancer comprises a shaft mounted impeller such as a screw conveyor, a spiral brush, or a paddle-blade configuration. The shaft of each device is attached radially on the main bit body with each shaft having a drive wheel mounted thereon adjacent the bit body periphery.