down-hole hammer drilling

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down-hole hammer drilling A method of drilling a borehole using a pneumatic, percussive hammer drill. The rock is fragmented by repeated impaction presented directly to it. This produces a medium-diameter hole, but drilling speed is slow so that operating costs tend to be high. The method is often used in drilling holes for a pre-split surface, since such holes have to be precisely located. See PERCUSSION BORING.

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