| 摘要 |
The apparatus, in one embodiment has guide housing with a shaft extending through the guide housing with a drill bit coupled to its forward end. The shaft may be moved to a forward drilling position or to a rearward shifting position relative to the guide housing. A cam is located inside of the guide housing. A cam follower is coupled to the shaft. In the shifting mode, the cam follower is disengaged from the cam. A clutch is provided for coupling the cam to the shaft when the shaft is in the shifting position such that the cam follower may be rotated with the shaft relative to the cam to allow the cam follower to engage the cam when the shaft is moved to the forward drilling position. In the forward drilling position of the shaft, the clutch release the cam from the shaft and the cam follower engages the cam to allow straight drilling to occur or to cause the axis of said guide housing to shift relative to the axis of the shaft to cause the direction of drilling by the shaft and drill bit to change. |
