Patent ID: 8721333

Claim:
An air-driven rotary cutting tool comprising: a grip part adapted to be held by an operator; a head part provided at a distal end of said grip part; and a rotor provided in a hollow portion formed in said head part with a bearing in between said rotor and said head part, said rotor being rotatable around a rotary axis thereof: said rotor comprising a first turbine blade portion provided with a plurality of first turbine vanes surrounding said rotary axis and a second turbine blade portion integrally formed with said first turbine blade portion and having a plurality of second turbine vanes surrounding said rotary axis; said head part including in said hollow portion an air supply port for emitting air into said first turbine blade portion of said rotor from an air supply passage provided at said grip part, a guide portion for guiding air from said first turbine blade portion into said second turbine blade portion, and an exhaust port for exhausting air from said second turbine blade portion to an exhaust passage provided at said grip part; and air emitted from said air supply port blowing into a first air channel provided between said first turbine vanes and activating said first turbine blade portion from a substantially perpendicular direction relative to said rotary axis of said rotor to rotate said rotor around an axial center of said rotary axis and being exhausted from said first air channel of said first turbine blade portion along an axial direction of said rotary axis, the air further being guided by a second air channel provided at said guide portion into a third air channel provided between said second turbine vanes of said second turbine blade portion, the air thus guided into said third air channel of said second turbine blade portion activating said second turbine blade portion in a direction substantially perpendicular to said rotary axis to further promote rotation of said rotor, and then the air being exhausted from said third air channel and into said exhaust port; wherein each of said plurality of first turbine vanes has such a concave shape on a side thereof seen in a direction into said rotary axis as to be concaved from an upstream side into a downstream side in a rotational direction of said rotor, while each of said second turbine vanes has such a concave shape on a side thereof as to fall be concaved into an opposite direction from said first turbine vanes.