Rock drilling equipment
In a reverse circulation down-the-hole hammer assembly a having a axially extending central tube ( 30 ) for recovery of drilling debris, the central tube ( 30 ) has a downwardly facing abutment ( 32 ) and an upwardly facing upper end and is located axially in the hammer assembly by having the part thereof between the downwardly facing abutment and the upper end located between axially spaced complementary abutments, one of which fixed and the other of which is provided by a resiliently longitudinally displaceable member ( 42 ) within a casing part providing an upper end of the hammer assembly and which is removably retained in an adjoining part of the hammer assembly. The longitudinally displaceable member engages the upper end of the central tube and thus clamps the central tube in place.
1. A drill bit for a reverse circulation rock drill, the drill bit having a head with a working face and a shank of reduced diameter as compared with the working face, the drill bit having one or more intake holes in the working face leading to a passage extending up the drill bit shank, the drill bit head having, at a location spaced from the working operative face, a circumferential band or collar providing a cylindrical external surface coaxial with the drill bit, the diameter of said circumferential band or collar being substantially equal to the effective diameter of the working face of the drill bit and not less than the diameter of any other part of the drill bit, the drill bit having a circumferential groove around its exterior, below said circumferential band or collar and having passages for exhaust air discharging into said groove, whereby such air can pass around the front of the drill bit and across said face to exit through said intake holes.
2. A drill bit according to claim 1 wherein the drill bit, below said circumferential groove has an exterior surface in the form of a cylinder interrupted by grooves extending longitudinally to the working face of the drill bit, for the passage of exhaust air to said working face from said circumferential groove.
3. A drill bit according to claim 1 wherein above said circumferential band or collar, the drill bit has a further circumferential groove, directly below a circumferential rib which is of reduced external diameter as compared with said circumferential band or collar and which is provided for engagement by a bit catcher sleeve.
4. A drill bit according to claim 2 wherein above said circumferential band or collard, the drill bit has a further circumferential groove, directly below a circumferential rib which is of reduced external diameter as compared with said circumferential band or collar and which is provided for engagement by a bit catcher sleeve.