François(?) Senot of France produced a screwcutting lathe (tour à tailler) in 1795. It is on display in the Musée des arts et métiers in Paris.
It is the earliest known surviving example of a large all-metal screwcutting lathe using change gears (un système d'engrenages interchangeables). The change wheels allowed a range of pitches to be cut from one leadscrew.
Musée des arts et métiers description of lathe here.
The lathe bed has two long wrought iron rails, each being assembled from three rectangular bars. The carriage slides on the top surface of the top bar. Four '[' shaped brackets at the corners of the carriage provide lateral guidance, and also prevent the carriage from being lifted off the guide rails (photo 10). The intermediate section of the side rails locates the headstock and tailstock transversely, while the upper surface of the lower bar serves to support the 'feet' of the headstock and tailstock (see photo 8).