What machine did Leonardo da Vinci design to manufacture screws automatically?

Leonardo da Vinci designed a screw-cutting machine to produce screws with greater regularity.

Screws require a consistent helical thread, and hand production makes identical parts difficult. Leonardo’s engineering drawings show mechanisms intended to guide a cutting tool along a rotating workpiece, helping create a repeatable thread. This was part of his wider interest in machine tools and the standardization of manufactured components.

The machine should not be confused with a general-purpose lathe. A lathe rotates a workpiece for many operations, while a screw-cutting machine is specifically arranged to generate a controlled helical thread. Leonardo’s design anticipated later developments in precision engineering.

As with many Leonardo inventions, the surviving evidence is primarily documentary. His notebooks contain proposals and mechanisms, but they do not prove that every design was built and used in a workshop. The historical importance is the clear mechanical solution to a demanding manufacturing problem.