Importance

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Abstract

A method and apparatus are disclosed for drilling a bore hole using a dual concentric drill pipe. Air is supplied through the outer pipe to the bit to cool the bit and jet cuttings upwardly in the bore hole to a suction inlet leading from the bore hole to the inner pipe. A negative pressure is applied to the inner pipe to bail the cuttings up the inner pipe. Makeup air flows down the annulus in the bore hole to the suction inlet and prevents upward movement of dust in the bore hole. A bore hole enlarging bit is disclosed and has expansible cutters which are expanded by hydraulic fluid pressure. In one form, the expansible cutters can also be retracted by hydraulic fluid pressure. The enlarging bit is employed to enlarge a pilot bore hole from a selected beginning location to the bottom of the pilot bore hole to form a blast chamber.

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First Claim