You lost me. Do you do this on the ground? You smash the ends? need a better explanation.
Not on the ground. My vise is mounted on my bench, so at that level. The pictures here are on the ground, but just for picture taking purposes.
Pinch a couple inches of one end in the vice until flat. Fold about a half inch over on itself. Then clamp with a vise-grip as tight as you can possibly get them.
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Take the other end and pinch 2-3” in the vice jaws tight enough that it’s impossible to pull out. It helps if the tubing is perpendicular to the jaws to prevent slipping out.
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Holding the vise-grip end in one hand with tubing parallel to the ground but vise-grips perpendicular to the tube, smack the back of the vise-grips just above your hands with a sledge a few times hard. It’ll finish straightening out the pipe perfectly.
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I sent these pics to a buddy to explain it. It’s better to have a helper. No matter the method of straightening the tube, if you pick it up by yourself and it’s a longer piece—it’s so soft it’ll droop slightly. That shouldn’t be an issue though, because the longest straight line between radii isn’t typically long enough to notice. But, if your careful, you can pick up longer pieces without them drooping under their own weight.