PURPOSE: To reduce the backlash and abrasion of a connection section and improve the life of parts by forming a coupling section between a head stem and a head sleeve into a circular cross section, and inserting pins at the position where they are overlapped to restrict idle rotation.
CONSTITUTION: A head stem 12 is screwed on an intermediate rod 6, and a head sleeve 13 is slidably and relatively unrotatably coupled with the outer periphery of the coupling section 12a of the head stem 12 with a circular cross section. Multiple forward bits 17 are fitted at the front end section of the head sleeve 13, and wing bits 21 are stored at the intermediate section. Multiple pins 32 are inserted at the position where the head stem 12 and the head sleeve 13 are overlapped to prevent the idle rotation of them. For drilling, a steel pipe 10 is fitted to the outer periphery of the intermediate rod 6 and held by a pipe holder, and a drilling section 7 is pressed to the surface of the natural ground. A hole is drilled by the forward bits 17, and the diameter is expanded by the wing bits 21. When drilling is completed, the steel pipe 10 is removed from the holder and left in the hole, and the drilling rod and the like are extracted to the outside.
KUNITAKE SEIJI
TSURUTA RYUJI
