From Villard de Honnecourt, Notebook,
Manuscript 19093, Paris, Bibliothèque Nationale de France.
Screw and animal-driven shaft power.
Two vertical mounts converging towards the top hold the screw in place on which the spiral moves; it is connected to an auto-blocking system for lifting stone blocks. The screw is turned by an underlying carousel, which is moved by manpower or perhaps by using draft animals.
Dimensions: the difficulty in creating very long screws makes one believe that this elevator could have been approximately 5-6 meters long maximum.
Reconstruction: screws of this size were very fragile and the lifting system, as it was designed, implicates noticeable lateral stresses, which could in a short time compromise its efficacy if not even break it. The load towing system was used in antiquity for lifting large stone blocks or molded marble. Nevertheless, even if this is the only lifting system documented in the notebook of a medieval architect, the fragility of the screw system brings doubt to its actual efficacy. Another problematic element that emerges from this design concerns the maneuverability of the lever. When the load is on the ground at the foot of the machine the lever cannot be turned. This problem could be solved by letting the lever slide so it only protrudes on one side after every half rotation of the screw. When the load is lifted above the lever, rotation could proceed normally.