To facilitate work during mounting a core bit 10 to a concrete drill 1 or removing therefrom, and enhance efficiency of a whole drilling work.
A mechanism is characterized by forming a circular guard part 15 to the outside periphery surface of the mounting part 13 of the core bit 10; forming a cylindrical member 16 receiving the mounting part 13 to a chuck part 6; forming an engaging means 17 comprising a plurality of irregular parts 18 and 19 formed at even intervals in a circuit direction reciprocally engaging between the side face of the guard part 15 of the core bit 10 and the edge face of the cylindrical member 16; and further providing with a retaining means 20 which retains the core bit 10 at a mounting position by engaging with the guard part 15 of the core bit 10 and a lock member 22 which locks and unlocks the retaining means 20 in a condition that the core bit 10 is retained at the mounting position to the chuck part 6.
YAMASHITA MICHIO
MURAKAMI NAOHIDE
