| 摘要 |
A rotary well drilling unit, particularly for water wells, comprises a tubular rotatable drill string string through which water is pumped. Attached to the lower end of the drill string is a drill head having side-by-side cutter blades. The cutter blades are cammed radially outwardly to expand in diameter when the drill string is lowered to drill a hole sized to receive a well casing lowered behind the drill, and are cammed radially inwardly so as to contract in diameter to clear the casing when the string is lifted. The same drill may be used for drilling wells of different diameters by merely substituting cutter blades.
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