Core bit
 A core bit includes a tube (2) having an opening end surface (21) in the axial direction and a plurality of tips (3) fixed to the opening end surface (21) of the tube (2). Each of the tips (3) includes an abrasive grain layer (31) that contains diamond abrasive grains and a binder for bonding the diamond abrasive grains to each other. The diamond abrasive grains contain not more than 0.03 weight % of inclusions. The inclusions contain iron and nickel as main components. The binder contains at least 0.1 weight % and not more than 2.0 weight % of graphite. The core bit has a short perforation time, i.e., a high cutting speed, excellent sharpness, excellent durability, and a long life. The core bit is suitable for boring a concrete structure. 
Osaka Diamond Industrial Co.
B
B28D
inventional
Shuichirou Tamotsu Eiji
Koroku Nakano Adachi