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Bending tubing without a bender, just heat

30K views 26 replies 15 participants last post by  jw_ 
#1 · (Edited)
A buddy and I are working on some parts and we need to bend some tubing. We don't have a bender, don't know someone with a bender, but do have a torch and a good place to start bending. We need to bend 1"x.120 wall and 3/4"x.109 wall mild steel tubing. I figured on making something to bend the tubing around and then heating it up just enough to carefully bend it. The bend needs to be more like a slight arc that doesn't have a constant radius and not anything real tight.

Is this going to make the tubing structurally unsafe in the end? Seen it done and used on frame parts, but never done this myself.
 
#27 ·
yea, i studied metallurgy when i was in school too. the problem with heating tubing to bend it is that with a torch, you don't have very good control over heating the tube evenly. what you end up with is a piece that is soft in places. just about every commercial frame you can name is bent cold, without work hardening being a concern. this only becomes a problem when steel is bent repeatedly.

also, you don't have to have a fancy bender to cold bend dom. you can bend it over a form just fine, as long as you have everything fastened down securely.

DosTrumps said:
Cold bending work-hardens metal, in this case the steel will have a residual stress in it from cold bending. If it is hot-bent, it will not have significant residual stresses in it (from the bending process), especially if it is cooled slowly. (BTW, "slowly" for low-carbon steel like 1018 means you can shove it in a bucket of water as soon as it has air-cooled a couple minutes; really controlled slow cooling is only important in alloys or high-carbon steel).
 
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