Abstract: A milling tool (3-5; 51-53) in combination with a stabilizer therefor has a milling tool with a body (51) with a plurality of radially extending and circumferential blades (3) diposed about the body. The lower portion of the body (51) has a portion (57) upon which is located a stabilizer (70), the stabilizer comprising a sleeve (71) about which are disposed a plurality of helically disposed fins (75). The sleeve (71) has an internal screw thread (73) for mating with an external screw thread (55) on the body (51).By providing a single milling tool on site and a plurality of separate pilot stabilizers so stabilizer sleeves can be quickly and easily secured to the milling tool thereby eliminating the necessity of cutting the fins to the required radial height when on site.

Abstract: A cutter for a downhole milling or cutting tool and a tool incorporating the blade has a longitudinal axis about which the tool is rotatable. The tool may have a plurality of circumferentially disposed blades which are either fixed or radially movable to perform a cutting operation. Each of the cutters has a blade having a cutting surface which is formed by a plurality of cutting elements. Each of the cutting elements has a cutting edge and a plurality of protruding ridges each of which are longitudinally spaced from one another and interspaced from one another by a recess portion so that in use swarf moves upwardly from a first cutting edge along the recess portion and is broken off when approaching the next, uppermost, ridge. By providing such relatively closely spaced ridges generally C-shaped swarf cuttings are produced and "birdnesting" is substantially reduced or eliminated. The cutting elements each have a cutting surface which presents a negative radial rake angle.

Abstract: A bottom hole assembly is described having a bit driven by a downhole motor and stabilizers located above the motor on the drill string. A subassembly is also provided for controlling the bit trajectory that is operational on demand at the rig site. The subassembly comprises an underreamer located directly above the bit. The underreamer is hydraulically actuated to retract and extend the cutters.