| 摘要 |
A drill bit 10 has a gauge region 18 which may be changed in use between a cylindrical profile for straight drilling, and a tapered, conical gauge profile for curved drilling. The gauge region 18 is intermediate a cutting face 12 and a connection 16 and comprises at least one hinged finger 20 or hinged gauge discs 30 comprising movable segments 32 which are actuated between a first position, in which the gauge region is bounded by an imaginary tubular or cylindrical surface of constant cross-section co-axial to the axis of rotation, and a second, tapered position in which a portion of the member is located radially inwards and bound by an imaginary three dimensional conical sectional surface. |
