Expansible rotary drill bit

摘要: A rotary drill bit having cutters expanded outwardly to a hole substantially greater in diameter than the maximum effective of with its fully retracted. The are mounted on expandable and retractable supporting members spaced circumferentially around bit, each member cluster thereon, being or radially from other, collectively cutting upon formation shoulder non-tracking relation. tool is locked hydraulically retracted position, unlocked permit expansion by fluid pressure. Air circulated down outside aerates liquid column within pipe connected tool, causing hydrostatic head externally flow across bottom toward axis flush cuttings, clean cool cutters, carry cuttings through suitable discharge point above top hole.