A machine tool comprises first and second support arms, and a rigid structure which couples the first support arm to the second support arm. A first rotary drive is operable to rotate the first support arm and the rigid structure relative to each other about a first rotational reference axis, and a second rotary drive is operable to rotate the second support arm and the rigid structure relative to each other about a second rotational reference axis, wherein the first and second rotational reference axes are parallel and spaced apart by a fixed distance. A control arrangement is configured to control the first and second rotary drives such that a workpiece mount carried by the second support arm follows a predetermined path relative to a tool mount carried by the first support arm in a plane perpendicular to the rotational reference axes.