Fully rotating rotary actuator of a multi-purpose machine in which an axle supports the frame of a felling head by a bearing mount, there being a rotary mechanism driven by a rotary motor between the axle and the frame, and in which the connection of the axle includes rotatable joints, the axle includes conduits for electrical cables and a processing fluid line, and in which an additive fluid line tube is arranged in the conduit in the axle and connected to its lower end is a rotatable connector, which is connected to a second tube fastened in the frame for the application of the additive fluid.