Abstract: A rotary cutting tool, which may be a reamer for enlarging an underground borehole or a mill to remove tubing by cutting into the inside wall of the tubing, has a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly includes a supporting structure bearing a sequence of cutters which extends axially along the tool with leading surfaces facing in a direction of rotation of the tool. The cutters of each sequence are positioned at a plurality of circumferential positions such that no more than three cutters of the sequence are aligned on any line parallel to the longitudinal axis of the tool. In an overlapping arrangement, a plurality of cutters in the sequence may have a leading face circumferentially behind the leading face but ahead of the trailing end of at least one other cutter.

Abstract: A reaming tool for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly includes a supporting structure bearing a sequence of cutters which have hard surfaces exposed and facing in a direction of rotation of the tool. The outer surface of the support structure on each cutter assembly includes zones which each face towards an end of the assembly and is configured such that as it extends circumferentially relative to the tool axis in the direction opposite to rotation of the tool, it also extends away from an end of the assembly.

Abstract: A reamer for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, and each cutter assembly comprises a supporting structure and a plurality of hard faced cutters (211-216) embedded therein with a hard face of each cutter exposed and facing in a direction of rotation of the tool. Each cutter assembly includes at least one outward-facing gauge surface (220), at a radial distance from the tool axis which aligns the gauge surface with the radially outer extremity (218) of at least one cutter. This gauge surface (220) extends (221) in the direction of rotation circumferentially ahead of the extremity of the exposed face of the aligned at least one cutter. It may meet the side of the assembly at a curved (222) or bevelled (342) edge and may also extend back from the exposed face of the cutter.

Abstract: A reamer for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool. Each cutter assembly comprises a supporting structure and a plurality of hard faced cutters secured therein with a hard surface of each cutter exposed and facing in a direction of rotation of the tool and extending radially outwards from the tool axis to a radially outward extremity. These cutters are arranged in a sequence extending axially along the tool. In contrast with convention a1 cutter assemblies, the supporting structure comprises at least one radially outward-facing surface which is positioned to follow behind the leading face of at least one cutter as the tool rotates and which is aligned with the radially outer extremity of the cutter at the same radial distance from the tool axis. Thus the surface area available to contact the borehole wall and stabilize the positioning and motion of the rotating reamer is enhanced.

Abstract: A reaming tool for enlarging an underground borehole comprises a plurality of cutter assemblies (251, 252, 253) distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly comprises support structure bearing a sequence of cutters (211-214) with leading surfaces facing in a direction of rotation of the tool and the sequence of cutters extends axially along the tool from an axial end (202) of the tool with the cutters positioned at radial distances from the tool axis which progressively increase as the sequence extends away from the axial end of the tool. The cutter assemblies include guiding structure (261-264) which is positioned circumferentially ahead of the leading faces of cutters of the sequence on the assembly.

Abstract: A reaming tool for enlarging an underground borehole has a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool. First, second and possibly more cutter assemblies each have an axially extending length comprising supporting structure bearing a sequence of cutters which have hard surfaces facing in a direction of rotation of the tool and are distributed axially along the length. A plurality of the cutters on the second cutter assembly are at axial positions relative to the tool which are intermediate between axial positions of the cutters on the first cutter assembly. Cutters on further assemblies may also be at intermediate axial positions. Cutters in the overall plurality of sequences are positioned at radial distances from the tool axis which increase as axial distance from an end of the tool increases.

Abstract: An expandable reamer for a borehole has a plurality of support elements (202) distributed around a central axis of the tool with cutters (234, 236) and stabilising pads (250) on the support elements, arranged such that at least one of the support elements comprises at least one region comprising cutters and at least one support element comprises a stabilising pad having a front surface positioned to face the wall of the borehole. The reamer includes drive mechanism for expanding the support elements (202) radially outwardly from the central axis. The support elements differ in the presence or axial positions of stabilising pads (250) thereon such that at least one support element differs from at least one other support element in the presence or axial position of at least one stabilising pad. This arrangement allows the stabilising pads to be positioned at or close to full gauge, thereby reducing vibration.

Abstract: A rotary cutting tool having a tool body insertable into a drill string with a plurality of projecting or extendable cutter assemblies at positions distributed azimuthally around the longitudinal axis of the tool body. Each cutter assembly includes a support structure bearing a plurality of cutters with exposed hard cutting surfaces facing in a direction of rotation of the tool. The support structure may have a surface positioned to contact a conduit wall and may be made as a body of particulate material infiltrated with a metal binder, where the particulate material may include material such as tungsten carbide having a Knoop hardness of at least 1000. The support structure may have a functionally graded composition with hard material to contact the wall and steel in a region which will be machined during manufacture.

Abstract: A downhole cutting tool which may be a reamer or a mill has a rotary tool body with at least one block which carries hard-faced cutters and projects or is extensible from the tool body. A radially outward facing part of the cutter block defines a channel for fluid flow which extends generally axially along the cutter block. The channel is configured such that at least the rotationally trailing edge of the channel extends along the block in one or more directions which are inclined relative to the tool axis. This reduces or avoids the amount of channel edge parallel to the tool axis and thereby mitigates whirling and/or or vibration.

Abstract: Tubing in a borehole is removed using a rotary milling tool comprising a plurality of elements projecting from or extensible from the body of the tool. The elements are distributed azimuthally around the tool body. The elements comprise cutters to remove material from the tubing and outward facing guide surfaces for sliding contact with an inner surface of the tubing. As the tool is rotated and advanced, forward cutters contact the inner surface removing material from the tubing and exposing a renewed interior tubing surface with a diameter swept out by the cutter. The outward facing guide surfaces extend the same distance from the tool body as the forward cutters producing a sliding contact with the newly created inward facing surface. Further cutters, disposed behind the outward facing guide surfaces, with respect to motion of the tool through the tubing, remove the remaining portion of the tubing.

Abstract: A reaming tool for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly includes a supporting structure bearing a sequence of cutters which have hard surfaces exposed and facing in a direction of rotation of the tool. The outer surface of the support structure on each cutter assembly includes zones which each face towards an end of the assembly and is configured such that as it extends circumferentially relative to the tool axis in the direction opposite to rotation of the tool, it also extends away from an end of the assembly.

Abstract: A reamer for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, and each cutter assembly comprises a supporting structure and a plurality of hard faced cutters (211-216) embedded therein with a hard face of each cutter exposed and facing in a direction of rotation of the tool. Each cutter assembly includes at least one outward-facing gauge surface (220), at a radial distance from the tool axis which aligns the gauge surface with the radially outer extremity (218) of at least one cutter. This gauge surface (220) extends (221) in the direction of rotation circumferentially ahead of the extremity of the exposed face of the aligned at least one cutter. It may meet the side of the assembly at a curved (222) or bevelled (342) edge and may also extend back from the exposed face of the cutter.

Abstract: A reaming tool for enlarging an underground borehole has a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool. First, second and possibly more cutter assemblies each have an axially extending length comprising supporting structure bearing a sequence of cutters which have hard surfaces facing in a direction of rotation of the tool and are distributed axially along the length. A plurality of the cutters on the second cutter assembly are at axial positions relative to the tool which are intermediate between axial positions of the cutters on the first cutter assembly. Cutters on further assemblies may also be at intermediate axial positions. Cutters in the overall plurality of sequences are positioned at radial distances from the tool axis which increase as axial distance from an end of the tool increases.

Abstract: A reamer for enlarging an underground borehole comprises a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool. Each cutter assembly comprises a supporting structure and a plurality of hard faced cutters secured therein with a hard surface of each cutter exposed and facing in a direction of rotation of the tool and extending radially outwards from the tool axis to a radially outward extremity. These cutters are arranged in a sequence extending axially along the tool. In contrast with convention a1 cutter assemblies, the supporting structure comprises at least one radially outward-facing surface which is positioned to follow behind the leading face of at least one cutter as the tool rotates and which is aligned with the radially outer extremity of the cutter at the same radial distance from the tool axis. Thus the surface area available to contact the borehole wall and stabilise the positioning and motion of the rotating reamer is enhanced.

Abstract: A rotary cutting tool, which may be a reamer for enlarging an underground borehole or a mill to remove tubing by cutting into the inside wall of the tubing, has a plurality of cutter assemblies distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly includes a supporting structure bearing a sequence of cutters which extends axially along the tool with leading surfaces facing in a direction of rotation of the tool. The cutters of each sequence are positioned at a plurality of circumferential positions such that no more than three cutters of the sequence are aligned on any line parallel to the longitudinal axis of the tool. In an overlapping arrangement, a plurality of cutters in the sequence may have a leading face circumferentially behind the leading face but ahead of the trailing end of at least one other cutter.

Abstract: A reaming tool for enlarging an underground borehole comprises a plurality of cutter assemblies (251, 252, 253) distributed azimuthally around a longitudinal axis of the tool, wherein each cutter assembly comprises support structure bearing a sequence of cutters (211-214) with leading surfaces facing in a direction of rotation of the tool and the sequence of cutters extends axially along the tool from an axial end (202) of the tool with the cutters positioned at radial distances from the tool axis which progressively increase as the sequence extends away from the axial end of the tool. The cutter assemblies include guiding structure (261-264) which is positioned circumferentially ahead of the leading faces of cutters of the sequence on the assembly.

Abstract: An expandable reamer for a borehole has a plurality of support elements (202) distributed around a central axis of the tool with cutters (234, 236) and stabilising pads (250) on the support elements, arranged such that at least one of the support elements comprises at least one region comprising cutters and at least one support element comprises a stabilising pad having a front surface positioned to face the wall of the borehole. The reamer includes drive mechanism for expanding the support elements (202) radially outwardly from the central axis. The support elements differ in the presence or axial positions of stabilising pads (250) thereon such that at least one support element differs from at least one other support element in the presence or axial position of at least one stabilising pad. This arrangement allows the stabilising pads to be positioned at or close to full gauge, thereby reducing vibration.