| 摘要 |
PROBLEM TO BE SOLVED: To accurately drill a hole arranged continuously with a preceding hole at a predetermined center-to-center distance in a predetermined bearing in a drilling device having a guide rod 5 supported on a rod holder 6 fitted to the portion of a drill rod 4 projecting forward of a centralizer 3 on a guide cell 1 and drilling the hole arranged continuously with the preceding hole with the guide rod inserted into the drilled preceding hole H1. SOLUTION: The guide rod 5 is longitudinally slidably inserted into the rod holder 6 at the small diameter part 52 thereof extending from the large diameter part 51 at the front end rearward. A stopper part 53 restraining the sliding of the guide rod 5 forward of the rod holder 6 at the stroke end position where the front end of the guide rod 5 is positioned forward of the front end of the drill rod 4 is installed on the guide rod 5. A guide part 31 for centering the guide rod 5 at a specified position in association with a stopper part 53 is installed on a centralizer 3. COPYRIGHT: (C)2008,JPO&INPIT
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