| 摘要 |
A drill bit for use with earth drilling equipment, the drill bit having a body and movable cutting members or blades variably positionable between a first position in which the diameter defined by the cutting members is generally equal to or less than the diameter of the drill bit body and a second position in which the diameter defined by the cutting members is greater than the diameter of the drill bit body. The second, expanded position is assumed by the cutting members when they are in contact with the bottom of a hole and are thereby urged upwardly relative to the bit body. The first, retracted position is assumed by the cutting members when the drill bit is being tripped into or out of the hole and, because the cutting members are essentially retracted relative to the bit body, the drill bit does not become jammed downhole. A fixed-blade adaptation of the invention is also contemplated.
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