In article ,
Chris Bacon writes:
Andrew Gabriel wrote:

Anneal the pipe only where
you want it to bend, pack it full of dry sand (molten lead is another
option, but a bit more messy;-).

Erm, molten lead? How is that going to work?

Copper tube was filled with it and capped off at both ends
during bending. The non-compressibility of the lead prevented
the tube collapsing during bending -- same effect as for dry
sand. I think molten lead was used (as opposed to water, say)
so the tube could be continually annealed during bending which
would be impossible with any liquid which boiled below
copper's annealing temperature. (I've got an old book on
copper tubing which describes this, but it's currently
stored in a box in different house, so this is from memory.)

--
Andrew Gabriel