Tim Watts wrote:

/Copper welding/

Would that work with pipes cut with a rotating pipe cutter? The ends
would be perfectly square, but slightly belled in.

Yes

Sounds slightly like brazing (I never got on with that, but it was iron
to iron). Now that you mention it, I've seen airconditioning units (big
15kW ones) where they "brazed" the pipes. Wonder if that was the same
thing, or whether they really meant "brazed".

If well done, you wouldn't notice the joins: (proper) brazing is brass,
so a gold colour. This stuff's easy, needs no flux, and it's
copper-coloured.

--
Rusty