Image Number 3 for United States Patent #6799646.
As a serial element of a drill string, the drill string is adjustably bent by rotating one end of the sub relative to the other end. The opposite ends rotate about a tilted center line such that in one rotational position the sub is straight. One half turn of one end relative to the other bends the sub to the maximum angle. Between straight and maximum bend, any angle can be achieved by control of the amount of the relative rotation between the opposite ends of the sub.