| 摘要 |
An underreamer (10) is formed for mounting into a drill string with a downstream drill bit, and comprises two concentric sleeve-shaped parts (12, 14) axially displaceable relative to one another, with a bore extending therethrough and radially movable cutting means (28), which are influenced by a mechanical activating device, which is arranged to make use of said relative movement to push out the cutting means (28) radially into an active position from a retracted inactive position, the activating device making use of opposite relative movement in order to allow the cutting means (28) to be brought back into their retracted inactive position. |
