| 摘要 |
An adjustable length jacking column (22) for supporting a cutting or drilling tool between spaced apart surfaces is disclosed. A speed drive (124) serves to quickly adjust the column sections (48,50) to an intermediate position closely corresponding to the distance between the spaced apart surfaces. A selectively engageable screw drive (126) is configured to shift the column sections (48,50) from the intermediate position to a secured position, in which the column length corresponds to fixed securement between the surfaces. The screw drive (126) is drivingly connected between the column sections (48,50) to shift the column sections (48,50) relative to one another when engaged, and is drivingly disconnected from at least one of the column sections (48,50) when disengaged so as to avoid interfering with relative shifting of the column sections (48,50) by the speed drive (124). |
