Model of screw-cutting machine from design of Leonardo da Vinci with four additional cogs

This model has been made in accordance with Leonardo da Vinci's design on MS B, folio 70 V, which was written in 1488 and 1489. Supported by bearings mounted on a table are two lead-screws which are geared to a crank which also turns the blank on which the thread is to be cut. The blank passes through a hole in the cutter housing on each side of which are nuts which thread the lead-screws. The cutter, which is wedged in its housing, traverses at a rate determined by the gear ratio. Change-wheels are provided so that screws of different pitch may be cut, and to accommodate wheels of different size the bearing blocks may be moved laterally.

The screw, which results, is of opposite hand to the lead-screws, but Leonardo incorrectly depicted all three screws with left-hand threads. Evidently Leonardo did not draw an existing machine and this suggests that the machine was an original conception quickly noted down with an error in detail.