Downhole milling device

摘要

A device for performing milling operations in an underground borehole comprises a toppling head (2) which is pivotably secured to a stator housing (1) and which is equipped with one or more rotatable mills (3, 4) which are in use pivoted together with the toppling head (2) into an extended position from the stator housing (1) to mill a window in a surrounding casing (23), or to underream the wellbore whilst the stator housing is rotated in the wellbore.