hope it helps. As it seems you are UK based, you also might inquire about a local model engineering club. Most of what I saw in the video was fairly generic stuff and may appeal to various hobbies centre around machining other than horology (and many model engineers also build clocks). The UK is the centre for model engineering, you might find that including that fraternity greatly increases the target market size
It seems an odd choice, but it may not do harm.
imo there is no reason to use a multiweight oil, but maybe there are good reasons I missed. I also don't see a reason to use a synthetic oil, won't hurt, but they are more money. Regular oils don't break down until 270F - there's some serious issues if that's a factor with a lathe . It seems a topic full of hyperbole and little expertise; there's one horology oil report claiming synthetic oils don't contain hydrocarbons! What nonsense..
Multiweight oil are designed for internal combustion engines where there's a big temperature swing. The low initial viscosity helps get oil pressure built up quickly and makes cold cranking easier. But the engine quickly gets up 220F or so and the oil operates at its high viscosity (oil viscosity is determined at a set temp, i.e. an oil of X viscosity means its X at 40C, it will have a very different viscosity at 110C).
Your lathe just doesn't go through the same temp swings, say -40 to +220 n the dead of winter so I don't see how a multigrade makes any sense....except maybe because is readily available?
In general with machines, motor oil is really frowned on because of the additives and detergents. They're are needed do deal with combustion, but not wanted in a gearbox/bearing bath. Watchmakers lathes are a total loss system so these objections I don't think matter much, but its worth mentioning in the context of machine tools and oils.
With a 0W20 run a low temps, you're really only going to see the "0". The zero isn't really zero, its just small, maybe the equivalent to ISO 3 or maybe 4. ( 0 Viscosity is superfluidity, liquid helium laboratory stuff).
So what really matters? That its a clean mineral oil (i.e. hydraulic oil) and of the right viscosity (singular)
So that's the real concern I had, Is ISO 3 or 4 enough? I'd have guessed no, but maybe. Most of these lathes don't come with a viscosity recommendation. Clock oils often recommended are afaik much higher than 3-4 but (snake?) oil marketing, while full of lofty claims, rarely even states the viscosity! . I suppose it can be overthought, these lathes seem to easily last 100 years with whatever is put into them,. So long as the oil is thick enough to keep the parts separate at speed, its thick enough. Still, i think synthetic and multigrade oils in a plan bearing are, well, just not required.
1970A 200ft Diver just in - missing crown and elapsed time ring. First steps in the restore. Note the Timex caseback tool. The movments began to run on windup but this will still go with a full cleaning and oiling. More to come -