US Patent 7467671 Drill bit with protection member

A method is provided for removing a body of selected material from the interior of a casing extending into a borehole formed in an earth formation. The method comprises lowering a drill bit for further drilling of the borehole, into the casing, the drill bit having a longitudinal axis of rotation during operation, the drill bit comprising rock cutting means, at least one protection member for protecting the inner surface of the casing from contact with the rock cutting means, each protection member being adapted to remove said selected material from the interior of the casing and being radially movable towards the inner surface of the casing, and control means for applying a radially outward force of controlled magnitude to the protection member. The drill bit is rotated in the casing, and the control means is operated so as to apply said radially outward force of controlled magnitude to the protection member.