EXCAVATING TOOL

摘要

PROBLEM TO BE SOLVED: To prevent a shaft from being damaged or broken by a load such as an impact force or a turning force acting during excavation to an excavating tool equipped with an expansion and shrinkage type bit. SOLUTION: A diameter-increasing bit 5 positioned in a diameter-increasing state is installed by making contact it to a wall surface of a recessed portion 4 in a placeable manner inside the recessed portion 4 in a shrunk diameter state formed at the outer periphery of a tip portion 1A of a shank device 1 rotated around a shaft line O and is made rotatable around a center shaft X deviated from the shaft line O; the tip surface 5H of the diameter-increasing bit 5 and the end surface 1D of the shank device 1 are made almost flush each other and chips 2 are planted; a sloped portion 8 is formed which directs toward the rear end side as it directs toward the outer peripheral side at the tip portion of the diameter-increasing bit 5 in a state of the enlarged diameter; and the position R where the sloped portion 8 begins to tilt is positioned at the inner side of the outer diameter D of the tip portion 1A of the shank device 1. COPYRIGHT: (C)2004,JPO&NCIPI