| 摘要 |
<p>Drilling apparatus, such as an underreamer (20) comprises a generally cylindrical tubular body (22) and two cutting blades (26, 27) pivotally mounted to the body and movable between a retracted position and an extended position. Each cutting blade has a retracted position minimum gauge cutting portion (36) and an extended position maximum gauge cutting portion (35), with the blades in the extended position the gauge cutting portions (35) extending axially and being located in a transverse plane on or forward of the blade pivot axis.</p> |
