A power tool 410 for medical procedures has a motor 414 coupled via a geared transmission to a rotary chuck 419. A first shaft 418 is attached to the chuck and is coupled to a larger driven gear 444 and a smaller driven gear 446. This first gear set engages with a second, driving gear set comprising a second shaft 442 and a larger driving gear 440 and a smaller driving gear 438. One of the shafts is moveable with respect to the other so that either: the smaller driving gear engages with the larger driven gear, delivering low speed, high torque output suitable for reaming； or the larger driving gear engages with the smaller driven gear, delivering high speed, low torque rotation suitable for drilling. A speed selector knob 420 may protrude from a housing 412 of the tool and is coupled to a fork which moves one of the gear sets axially to select the output mode.
