What type of machine did Leonardo da Vinci design to make screws automatically?

Leonardo da Vinci designed a thread-cutting machine to make screws automatically.

A thread-cutting machine forms the helical ridge, or thread, on a screw or inside a nut. Leonardo’s mechanical drawings included arrangements of gears, guides, and cutting tools intended to coordinate rotation with the movement of the workpiece. That coordination was essential because the cutting tool had to advance at a controlled rate for the thread to remain even.

Before industrial machine tools, screws were often made by hand, making consistent size and spacing difficult. Leonardo’s design reflects his interest in repeatable manufacturing and in replacing skilled manual alignment with mechanical control.

The machine should not be confused with a modern lathe in every detail. Renaissance drawings often show proposed mechanisms rather than complete, tested production equipment, and Leonardo’s surviving sketches do not establish that his machine entered regular use. Nevertheless, the design belongs to the history of screw-cutting and anticipates the broader development of precision machine tools.