| 摘要 |
PROBLEM TO BE SOLVED: To excavate a borehole with a cross section matching the purpose of use. SOLUTION: This polygonal hole excavating device excavates a borehole by rotating a cutter device mounted on its end. The cutter device comprises a rotating bit main body 36 and a planetary cutter 42 provided on the bit main body 36 to revolve on its own axis while rotating about the rotation center O of the bit main body 36. A borehole with a polygonal cross section is excavated by shaping the contour of the planetary cutter 42 corresponding to the ratio of the number of revolutions of the planetary cutter 42 to the number of its revolutions. |
