| 摘要 |
Drill unit provided with a hydraulic or pneumatic hammer device 1 for drilling a hole or tunnel in the earth, in which unit the hammer device 1 is placed in the tip of the drill unit so as to produce hammer blows for one or more cutters 4, 6, 7 belonging to the cutter assembly, and the hammer device 1 contains a movable piston 2 which produces hammer blows. The centremost cutter 4 incorporates a joint face 12, which is known per se, for joining together ring cutters 6 of different sizes so as to increase the drill diameter in the cutter assembly, since at least the first ring cutter 6 which increases drill diameter can be withdrawn from the hole with the cutter 4, and at least the outermost 7 of the plurality of ring cutters which increase drill diameter can be left in the hole. <IMAGE>
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