Making a screw with a regular thread is a mechanical challenge. Until the 18th century, the turner manually gouged out a helical groove by gradually exerting pressure on the chisel. François Senot, preoccupied by the quality of the thread, improved solutions devised by Vaucanson and master clockmakers. The cutting tool carriage is mounted on a worm drive, the perfection of whose thread ensures the tool’s regular advance and constant pressure. A gear train with interchangeable gears synchronises the rotation of the piece to be cut and the worm drive. The thread pitch can easily be modified by changing the gear ratios. All kinds of screw threads could thus be perfectly executed. The advent of large metal lathes in the 19th century enabled the precise turning of the large metallic components essential for industrial machine tools.