Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

I've had some luck sawing a groove across the width of a scrap of 2x4 about twice or thrice as deep as the tubing is in diameter, and just barely wider, so that even with a few wabbles in it, the tubing can be forced easily into the groove. Find a thin strip of wood or other material that is not too hard which will fit into the groove essentially trapping the tubing. Rotate the tubing back and forth a little at a time while lightly tapping on the thin strip. Actual bends in the tubing can be nearly straightened by hand when they are up against the edge of the 2x4, then fed into the slot and treated with more rotating and tapping until you have fed the entire length of the tubing through the groove. At this point it should be pretty straight, but if not quite straight enough for your taste, then run through the whole process again, which should go much quicker the second time.

If your copper tubing seems unusually stiff when you first start, you should pull it out and anneal the entire length of the tubing, but after doing that, make all of your tapping and bending be very gentle, as your tubing will be very soft after being annealed.