Abstract: A method and apparatus that comprises releasably securing a milling tool to a deflecting tool using a securing mechanism. The securing mechanism comprises a member that is adapted to be broken by milling action of the milling tool. In addition, in some arrangements, a protective mechanism protects abrasive inserts on a pilot mill of the milling tool.

Abstract: A method and apparatus for predictable downhole milling of a casing window having predetermined location, orientation, dimension and contour geometry. An elongate substantially rigid milling shaft has at least one casing window milling element in fixed relation therewith and has a pilot mill in articulated and rotary driven connection with the milling shaft. The milling shaft is in articulated and rotary driven connection with a rotary drive mechanism. The articulated connection of the pilot mill and milling shaft may incorporate an articulation control system to permit the pilot mill to be maintained substantially coaxial with the milling shaft so that its trajectory at a predetermined stage of window milling can be controlled by the milling shaft when positive guiding by a deflecting tool can no longer be ensured.