Standard Seitz jewels are sized in 0.01mm hole increments up to 0.20mm, from there they go in 0.02mm increments. In industry makers would order jewels from specialist makers, to whatever size they wanted. In general the outer diameters would correspond to normal 0.10mm increments but the hole sizes could be anything- one common size I see is a 0.25mm hole, which isn't in the Seitz offering. What are your actual pivot sizes? Thankfully, at 0.20mm and up an extra 0.01mm of wiggle room usually doesn't affect performance. Do any of the suppliers have a 22/120 and 32/160?
Brilliant, many many thanks for your reply and help I will now have an afternoon tinkering with my lathes to see how it works.I have a Lorch lathe with lots of accessories and I have just bought myself a brand new Proxxon lathe as I'm retired and have lots of time (no pun meant) to tinker with old watches.Take care,keep safe and many thanks ,Regards,Seth.
That screwplate appears to be metric. So the sizes listed are the thread size, 20 is 2mm, 13 would be 1.3mm. So you would want to start with 1.3mm as your diameter. But- it might (probably) not cut the thread so much as cut and form the thread by displacing metal. I say that because it looks a little dubious in quality. So try a little smaller and see if you get a good thread form. You can turn a taper from say 1.15 to 1.3, and then thread that, and see where along the taper you get a full thread. Make a note of it for the next time you need to thread that size.
The old Martin screwplates had a screwy (haha) numbering system. There were two main designations from Martin, L and B; both seem to have the same thread diameters regarding their numbering, the difference is the pitch of the thread. Martin G plates were for left hand threads. Funnily enough, the "backward" numbering system for watch stems and crowns corresponds to the Martin sizing, I guess it was taken up at a time when Martin screwplates were the primary threading tool for watchmakers. 99% of the time I use industrially made metric taps and dies for threading, but sometimes for an old piece I will use a Martin plate. The threads are a little more rounded on their crests. I find that for a given size I need to turn a little undersize, as mentioned above. With new "real" metric stuff I turn to the nominal diameter.
Watch was working fine until I tried the Chronograph function. Everything works fine but the chronograph. It won’t reset back to 12. Just lingers around wherever it wants to go back to. Logic tells me it’s grease or broken/damaged spring or both. Found a bit if a rusty portion on the top pusher. Gonna have to try and take this boy apart.. any help will be greatly appreciated.
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