What precision device did Leonardo da Vinci design to cut screw threads accurately?

Leonardo da Vinci designed a thread-cutting machine to produce screw threads with greater precision.

Screw threads were valuable in Renaissance engineering because they could join parts, convert rotation into linear motion, and create adjustable mechanisms. Leonardo’s workshop drawings explore machines that guide a cutting tool along a rotating workpiece, coordinating the tool’s movement with the rotation needed to form a regular thread.

The design reflects an important shift from manually made components toward repeatable mechanical production. Accurate threads are difficult to cut by hand because the pitch must remain consistent along the entire length. A guided machine could improve uniformity and make interchangeable parts more practical.

Leonardo’s concept should not be confused with the modern industrial screw-cutting lathe, which developed through later improvements in lead screws, gearing, and machine-tool construction. Nor is every Renaissance drawing of a rotating workpiece a thread-cutting machine. The specific feature is coordinated movement that lets a tool generate a regular helical groove.