| 摘要 |
<p>The head of the drill has a first inclined deflecting surface (18), which is attached to the body of the drill. At least one further deflecting surface (24) is fixed to a part (10) of the drill, which can rotate about the longitudinal axis of the drill, and whose angular position relative to the first deflecting surface can be controlled. The deflecting surfaces can each take the form of a cam (22) projecting radially outwards from the circumference of the drill. The use of stops to retain the relative angular position of the deflecting surfaces at either 0 or 180 degrees, is also envisaged.</p> |
