Re: Answer
The tool was the lathe. The part I was looking for was the lead screw. A precision screw that permitted duplication of turned parts. Leonardo got credit for the screw and even made drawings of how it might be constructed but there is no record that he actually built one. In the 1780's, the French inventor Jacques de Vaucanson (1709-82) built a lathe with a sliding tool carriage, advanced by a long screw. Then almost simultaneously in 1797, Henry Maudslay (1771-1831) in England and David Wilkinson (1771-1852) in the U.S. improved this lathe by adding a sliding tool carriage geared to the spindle. By this means, the carriage mounted with a cutting tool was able to move in synchronicity with the spindle at a constant speed and the cutting of accurate and repetitive screw threads became possible. This breakthrough heralded the age of mass production and interchangeable parts. Jefferson in 1798, told Eli Whitney about it and Whitney then used it at his weapons manufacturing plant in New Haven, CT. As happened more than once, Whitney claimed the invention and never conceded that it was someone else�s invention. Many history texts still credit Whitney with the invention of the Milling Machine which he never would have invented without Jefferson's heads up and those before him.