| 摘要 |
A borehole drill construction comprising a cylindrical casing (l0), a chuck (ll) mounted on one end of the casing by means of a screw-thread and a cutter head (l2) carried by the chuck. The chuck has at least one axially projecting dog (ll<b>) thereon which is received in a corresponding recess (l2<b>) in the cutter head to provide a means to transmit torque from the casing to the cutter head via the chuck. The cutter head (l2) is retained on the bit by at least one plug (l3) projecting into a slot in the cutter head, which is permitted limited axial movement thereby. |
