| 摘要 |
<p>The invention relates to improvements in drills for undercutting holes and in particular to expansible drills. The drill according to the invention comprises a rotatable tubular drill body (11) having an axial bore, at least one radially extending arm (16) attached by hinge means at one end to the drill body (11) such that the arm is pivotal radially outwards, cutting means formed in the arm, guide means for moving the arm radially outwards, said guide means comprising a non-rotating shaft (22), and means (23) for moving the shaft axially relative to the drill body (11) towards said one end, so as to cause the arm to pivot radially outwards. <IMAGE></p> |
