Patent ID: 6789632
Filing Date: 2004-09-14
Classification: E21B

Abstract:
A rock drilling apparatus including a drill string terminating in a drill chuck and a drill bit detachably fitted into the drill chuck, the drill bit having a shank received in the drill chuck, the drill chuck and the drill bit shank having complementary non circular cross-section portions allowing rotational movement about the drill axis to be imparted to the drill bit via the drill chuck whilst allowing limited longitudinal movement of the drill chuck relative to the drill bit, the drill bit shank and the chuck having complementary formations above a first location along the drill bit, for limiting downward movement of the drill bit in the drill chuck, the drill bit having a drill head at its lower end which is of greater diameter than said shank, said head having a retaining formation above said lower end and below said first location which is of greater diameter than the drill bit is at said first location, which retaining formation co-operates with complementary retaining means on said chuck so as to prevent the complete detachment of said drill bit head from the chuck in the event of a fracture of the drill bit at said first location, and wherein said retaining formation on the drill bit head and the complementary retaining formation on the chuck take the form of respective parts of a bayonet connection arrangement which is substantially unstressed in normal operation of the drill, the arrangement being such that, in normal operation, the weight of the drill string, and the weight of the drill bit during lifting of the drill string, are supported by said complementary formations above said first location which likewise receive the stresses imparted to the drill bit to cause a rotational movement of the drill bit.