Patent ID: 7140456
Filing Date: 2006-11-28
Classification: E21B,Y10T

Abstract:
1. A cutting auger comprising: a first cutting device mounted on a first drive core for rotation about a longitudinal axis of the first drive core; the first cutting device comprising a first helical flight coaxially surrounding the first drive core with a first cutting arrangement at an axial end of the first cutting device such that, when the first cutting device is rotated, the first cutting arrangement and the first helical flight rotate at a common first rate of rotation; the first cutting arrangement having an outermost cutting point of its cutting action at a location which generates a cutting diameter of the first cutting device which is equal in diameter to an outer diameter of the first helical flight such that, when rotated, the first cutting element cuts a hole equal in diameter to an outer diameter of the first helical flight and the first helical flight carries the cut material away from the first cutting arrangement; a second cutting device mounted on a second drive core for rotation about a longitudinal axis of the second drive core; the second cutting device comprising a second helical flight coaxially surrounding the second drive core with a second cutting arrangement at an axial end of the second cutting device such that, when the second cutting device is rotated, the second cutting arrangement and the second helical flight rotate at a common second rate of rotation; the second cutting arrangement having an outermost cutting point of its cutting action at a location which generates a cutting diameter of the second cutting device which is equal in diameter to an outer diameter of the second helical flight such that, when rotated, the second cutting element cuts a hole equal in diameter to an outer diameter of the second helical flight and the second helical flight carries the cut material away from the second cutting arrangement; the second cutting device being coaxial with the first cutting device and arranged with the second cutting arrangement thereof axially in advance of the first cutting arrangement; the first and second helical flights being arranged with the helical turns of the first helical flight in opposed angular direction to the helical turns of the second helical flight; and a drive assembly arranged to rotate the first cutting device in opposed direction to that of the second cutting device; the outermost cutting point of the second cutting arrangement defining the cutting diameter of the second cutting device which is smaller than the cutting diameter generated by the first cutting arrangement such that an outer annular portion of the first cutting arrangement of the first cutting device effects a cutting action to generate a hole greater in diameter than the second cutting arrangement; the drive assembly being arranged to drive the first cutting device at a first speed and to drive the second cutting device at a second speed with the first and second speeds arranged such that torque generated by the cutting action of the first cutting device in one direction substantially balances torque generated by the cutting action of the second cutting device in the opposite direction.