A rotor disc brake lathe for simultaneously machining both left- and right-hand disc brake rotors of a vehicle wherein the rotors are mounted on opposite ends of a centrally supported horizontal drive shaft, and a pair of tool arm assemblies are mounted on both opposite end regions of a horizontal cross arm which is moved vertically on machine ways to effect selective engagement with and machining of the rotors. A spring biased vibration dampener is mounted on one of each pair of tool arms for engagement with one side of each rotor during the machining operation. A clutch mechanism to allow selective manual or motor driven vertical feed of the cross arm is provided.