| 摘要 |
A plurality of cutting faces is attached sequentially at a distal end of a drill string. The forward most cutting face that is distal to the top of the hole is exposed and used for drilling until worn to a point of inefficiency. The forward most or distal cutting face is then detached, exposing the next cutting face in the sequence. Detachment of the forward most cutting face is performed by remote actuation at the top of the drill string and/or outside the hole. A new cutting face is provided without the necessity of removing the drill string. The detachment process is repeated as long as drilling is continued and cutting faces remain. |
