REAMER

摘要

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 al 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.