| 摘要 |
PROBLEM TO BE SOLVED: To rotationally arrange many roller bits in a small area, facilitate the replacement of the consumed or worn roller bit, and realize a large digging diameter without necessitating a special bit when digging the natural ground composed of rock-bed layers at a small diameter. SOLUTION: A boring machine is constituted such that a cutter head A digging the natural ground is provided at a tip, and two cone bits 23 having a plurality of tapered faces 23a to 23d continuous with a first spoke 22 passing the center of the cutter head A and forming one end like a pointed end are arranged by bringing parts like pointed end close to each other and are rotatably attached to a saddle 30b provided in a detachable bracket 30. Two conical bits 25 having a plurality of tapered faces 25a to 25d continuous with a second spoke 24 crossing the first spoke 22 orthogonally and formed like truncated cones are arranged, and either of them is arranged so that an end part corresponds to a target digging diameter.
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