Quick change drill bit for use in tunnel or salt mine has flat shoulder with centering chamfer and has threaded off-center peg engaging threaded side of blind bore in drilling rod

摘要

The rotary drill bit has the usual type of cutting head (1) with a flat rear face forming a shoulder (3). It has a central raised area with a circular chamfered edge (4). It engages a matching flat area (7) with a chamfered edge (6) on the end of a drill rod (5). An off-center threaded peg (2) on the drill bit is forced against the side of a larger-diameter blind bore centrally positioned in the end of the drill rod locking the drill bit in position.