Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

This video gives a good explanation of setting up the change gears:
https://youtu.be/LyfaYy-20mU?si=sE9luwK2JbxSbgXR

Very good presentation as is typical of these "tubalcain" videos produced by mrpete222. Though made featuring the South Bend lathe, it is still perfectly applicable to my Atlas 618 lathe, and most any other gear change lathe out there!

One perhaps somewhat crucial point that I didn't hear him mention was that although both the South Bend lathe he used and my Atlas lathe are specifically designed and set up to work in English (Imperial) measure, and thus cut threads in that system, it is quite possible to cut adequate and useable, though perhaps not quite perfect, metric threads with these machines if they are provided with two critical change gears, that being one of 44 teeth and one with 52 teeth, the ratio thus formed (44/52 or .846154) very closely approximates a function of 2.54, which is the English to Metric ratio!