Re: metric threads:


Phillip Rankin
 

I am going to assume you have either a 9" workshop model A (commonly called a 9a) lathe or a 10k model A. When shipped from the factory these lathes came with three change gears. You should have a 20 tooth, a 40 tooth, and a 56 tooth. You should also have a large 80 tooth idler gear between the stud gear and the gear on the gear box. To cut the range of imperial threads (threads per inch) listed on the tag that should be attached to the gear box, the 56 tooth gear should be on the gear box. Then40 tooth gear is stored with thevery56 tooth gear when not in use. The 20 tooth gear should be on the stud above the idler gear for all the thread possibilities on the gear box tag except the very top row (4, 5, 5-1/2, 5-3/4, 6, 7). To cut the threads on the top row the 20 tooth gear is replaced by the 40 tooth gear. That cover the imperial threads these lathes we're designed to cut.

Cutting metric threads on a imperial lathe can be a bit tricky, but there are several ways to do it so before we go any further I have to ask, is there a specific metric thread pitch that you would like to cut? A certain range of threads? Or a full range of metrics? How accurate do you want to be? There is only one way to cut dead on metric threads with these lathes, and judging by the prices for the gear sets to do it on eBay, it is quite expensive. I'll try to help you set up, but I really need to know how much or how little you want to do. Your answer will determine which path we will take from here.

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