| 摘要 |
PROBLEM TO BE SOLVED: To provide an excavation device of a structure capable of reliably holding the state of the enlarged diameter of enlarging/contracting bits. SOLUTION: A fixed-diameter preceding bit 7 which precedes the enlarging/ contracting bit 6 and enlarging/contracting bit 6 enlarged and contracted in the radial direction by rotating about the axis which intersects the axis of excavation is provided with a bit assembly 3 pivoted at a main shaft 5, used for impact-type excavation to exert a striking force and excavate by an impact- type excavator and a down-the-hole hammer, and provided with both a rear shaft 8 of which the movement is interlocked with movements in the direction and reverse direction of excavation and a sandwiching mechanism provided at a section opposite to the rear shaft 8 and the enlarging/contracting bits 6 to enlarge and contract the enlarging/contracting bits 6 by sandwiching and releasing the enlarging/contracting bits 6 by the movements of the rear shaft 8.
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