That’s a very nice thing because not everyone can afford to have the treasures repaired.

I use this not the cheapest but you can’t put a price on health, although to late for me as just been told I have lung cancer 3rd lot. https://www.zoro.co.uk/shop/safety/reusable-respirators/maintenance-free-half-mask-ffa1p2-r-d-filters-4251%2B/p/ZT1259816X?utm_source=google&utm_campaign=pla%2B|%2BSafety&utm_term=ZT1259816X&utm_medium=pla_css_2&targetid=pla-836629170162&loc_physical_ms=1006631&dev=t&gad_source=1&gad_campaignid=6448151743&gbraid=0AAAAADgXECPDnqu608xTy3nfqW7s5R1xS&gclid=CjwKCAjw24vBBhABEiwANFG7y2ikTC4ddmbyopEYqlYo1zzDlg8kBYmd3JZWoIb7HZJfRiep-zmigBoCGOcQAvD_BwE

Thanks for the words of encouragement. It's about x3 the diameter unwound. It's about 30mm unwound and I measured the barrel internal diameter as 9.9mm. Not much about this movement was in good order, but I'm working towards that. At least the train runs now, although a bit more noisily than I'd like. For now, I'll clean the spring, arbor and barrel, give the spring a light coat of Moebius 8200 then put the it back in the barrel. If it turns out when the watch is running (which is still some way off) that I'm getting less than 90 or so degrees of amplitude or that it runs for less than a full day, I'll reconsider what to do with the mainspring then.

@Mark Sorry, I don't get what you mean by "I've split this into a new topic."?

My second suspect would be the O1 tool steel. Is it still "soft" enough after the turning operation? If the part got hot, it might be work hardened, making it more difficult to thread and easier to break.