Patent ID: 8113301

Claim:
An apparatus for earth boring, comprising: a tubular body having one end for securing to a drill string and another end for securing to a drill bit; a passage extending through the body along a longitudinal axis of the body; a plurality of arms pivotally mounted to the body and movable between a retracted position and an extended position, each of the arms having a face containing a plurality of cutting elements mounted thereon; an actuator mandrel carried in the passage, the actuator mandrel being axially movable from an upstream position to a downstream position in response to drilling fluid being pumped down the drill string, the actuator mandrel being cooperatively engaged with the arms for moving the arms to the extended position when the actuator mandrel moves to the downstream position; a plurality of body ports extending through a sidewall of the body, each body port being adjacent the face of one of the arms when the arms are in the extended position; and a plurality of mandrel ports extending through a sidewall of the mandrel, each of the mandrel ports being axially offset from one of the body ports while the mandrel is in the upstream position and aligned with one of the body ports while the mandrel is in the downstream position for discharging a portion of the drilling fluid across the face of one of the arms; a liner located within and axially movable with the mandrel, the liner being formed of a more wear resistant material than the mandrel; and wherein the mandrel ports extend through the liner.