NASA NTRS · 19700000377
Core drill's bit is replaceable without withdrawal of drill stem - A concept
Abstract
Drill bit is divided into several sectors. When collapsed, the outside diameter is forced down the drill stem, when it reaches bottom the sectors are forced outward and form a cutting bit. A dulled bit is retracted by reversal of this procedure.
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Rushing, F. C., Simon, A. B.. 1970-09-01. Core drill's bit is replaceable without withdrawal of drill stem - A concept. https://ntrs.nasa.gov/citations/19700000377
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