Roller cutter drilling bit for bore holes achieving high cutting efficiency

摘要

A roller-cutter drilling bit (1) for bore holes, has a main carrier (2) with connector (3) for the drill string and at least two cutters (4, 4') at the other end. These have convex surfaces (5, 5'). An axis of symmetry (S) of the bit aligns with the central axis of the borehole. Cutters rotate relative to, and on the carrier, about their own axes (K1, K2). These axes describe a conical surface in rotating about the main axis (S). The included angle phi and the cutter surfaces are selected to ensure self-acting rotation of the cutters relative to the carrier, during drilling. The significant novel feature is that one rotary cutter only, intersects the axis of symmetry (S) of the bit. The other cutter(s) (4') is undercut (7); so dimensioned and arranged to rotate freely with its neighbour(s).