| 摘要 |
An apparatus (1) for the directional drilling of a bore hole through a solid substrate includes a main bore head (2) mounted for rotation on a flexible drive shaft (10) and a pilot bore head (4) for weakening a region of substrate in advance of the main bore head, the weakened region being eccentrically located relative to the main bore head. The apparatus further includes means for enabling the drilling access of the main bore head, during subsequent drilling of the bore hole, to become substantially aligned with the weakened region of substrate. |
