| 摘要 |
The invention relates to improvements in drills for drilling and undercutting holes and in particular to an expansible drill. Such a drill (10) comprises a rotatable tubular drill body (11) having bore cutting means (14) at one end thereof, at least one undercutting arm (17) located within a slot (16) in the drill body attached by hinge means such that at least a part of the arm is pivotal radially outwards, guide means (12) for moving the arm radially outwards, said guide means comprising a shaft which is located within the drill body and constrained to rotate therewith, the drill further comprising locking means (30,40,41) for selectively preventing or allowing the shaft to move axially relative to the drill body as force is applied to an end of the shaft. |
