| 摘要 |
<p>A variable geometry cluster drill for rockboring comprising a central support (11) having a longitudinal axis about which the drill is capable of rotating to bore a hole. The drill also comprises a plurality of elongate hammers (14) located about the central support (11), each hammer (14) having a drill bit (16) at one end. At least one hammer (14) is pivotally mounted to the central support (11) so that the drill bit (16) thereof is capable of radial movement away from or towards the central support (11) between an operative position and an inoperative position, the diameter of the rotation path of the drill bit (16) in the operative position being greater than in the inoperative position. The cental support (11) also including means (17, 18, 19, 20) for controlling the radial movement of the drill bit (16) between the operative and inoperative positions.</p> |
