| 摘要 |
A process for drilling a hole with the use of a rotary and hammering tool 1, 2, in which process a guard tube 3 is drawn into the hole during drilling by means of pulling members, like lugs 4, belonging to the cutter assembly 2, 5. The drawing of the guard tube 3 is concluded at a desired depth by rotating the cutter assembly in the opposite direction so as to release the lug 5 from the cutter assembly drawing the guard tube 3, after which the drilling is resumed and the hole diameter remains unaltered. <IMAGE>
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