Abstract: A braking system for a powered rotary tool of the type in which a shaft is rotated about an axis by a motor includes a first brake element mounted for rotation with the shaft; a second brake element which is restrained from rotation; a biasing member normally urging the first brake element in an axial direction into braking contact with the second brake element and a brake release subsystem, the brake release subsystem to release the braking contact between the first and second brake elements upon start-up of the motor. On start-up of the motor, the shaft is free to rotate through a small angle of rotation before initiating rotation of the first brake element. The release subsystem includes at lease one pair of co-operating ramp surfaces, one of the ramp surfaces being arranged for rotation with the shaft and the other of the ramp surfaces being arranged for rotation with the first brake element. The braking system of the present invention is particularly suitable for use on a rotary-blade lawn mower.