The tool spindle has a sleeve bearing with the gas medium admitted centrally (7) between shank tool (1) and drive rotor (3). Orifice plates (5) at each end of the bearing restrict the flow of gas exhausting parallel and radially to the shank tool (1) and the drive rotor (3). Use of the orifice plates raises pressure in the radial bearing region without an increase in the flow of gas thus increasing the rigidity of the bearing support. The orifice plates (5) are made of copper for good conduction of heat away from the hottest parts.
