Dust evacuation for a hollow drill.

摘要

A drilling tool (22) rotated by a driving source is of cylindrical shape provided with a chamber (23) inside and intended to drill a ring-shaped hole (42) in a surface to be drilled. A pumping means (34) is arranged to suck air from the lower end of the drilling tool into the chamber (23) through the ring-shaped hole (42) which is being drilled and to discharged air outside the chamber (23). The drilling tool (22) has a blade which is so shaped as to provide outer und inner clearances in the ring-shaped hole (42) to suck air as a high speed air flow into the chamber (23) through the ring-shaped hole (42). The chamber (23) of the drilling tool has a large cross-sectional area relative to that of the outer and inner clearances in the ring-shaped hole (42) so as to quickly slow down the air sucked in the chamber (23).