| 摘要 |
PROBLEM TO BE SOLVED: To provide a boring device enabling the replacement of the cutting edge of a casing metal without pulling back a casing pipe to the ground and capable of increasing drilling efficiency by preventing the back-filling of an excavated portion. SOLUTION: A base stage tip block 34, an intermediate stage tip block 35, and a lower stage tip block 36 are connected to each other by inserting male screws 38 into vertically passed female screw through holes 39a formed in the tip blocks 34, 35, and 36 and threadedly tightening the tip blocks to the female screw holes 39b. The intermediate stage tip block 35 and the lower stage tip block 36 are formed to to be disassembled into four plane circular arc (quarter round-shaped) vertically split pieces 35a or 36a. When the tip block 36 is split into four split pieces 36a when the tip portion of the lowermost stage tip block 36 including the cutting edge tip 37 is worn to the lower end part of a cut-in line 40, the cutting edge tip 37 which is the tip part of the next stage tip block 35 is exposed. COPYRIGHT: (C)2006,JPO&NCIPI
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