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  1. #1
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    Default Bending tube with a TIG torch

    I welded some 1" x 1/8" thick tube into a T today. The "top" of the T warped slightly, of course. I know one way to bend it back is to weld a bead on the back side of the joint; I believe the bead should be perpendicular to the length of the tube, is that right?

    I was also wondering if I could bend it back just by heating the back side with my TIG torch, but not to such a heat that the metal actually melted. Some web searching indicates that I'm not the first to suggest this, but I'd love to hear if others think it would work. That would save me having to grind off the weld after the fact--and, of course, give me more opportunity to use my awesome TIG setup!

  2. #2
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    grab a strait piece of left over tube and try it first. You will need to figure out how big of a spot to heat.
    And don't forget to let it cool off. The bending happens uppon cooling. Several attempts will heat the whole part so that your target spot won't cool quickly.
    Dan H.

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    Default Re: Bending tube with a TIG torch

    Well, here's what I found.

    The TIG torch, as you would expect, was more than capable of heating a 1" square section of the tube to red hot. I used about 80 amps at first, then stepped up to 100 when that didn't do it. Bottom line: simply heating the tube to red hot is insufficient to cause it warp all on its own. Next, I intentionally built up a melted spot about 1" in diameter and let it cool. No dice. Finally, I put a huge blob of 7018 onto it--probably about 1/4 to 1/3 of a rod, and I intentionally washed down onto the side a little bit in case that mattered. No dice. The piece of scrap is still perfectly straight.

    So... I dunno. Apparently, if I put down 4" of weld around a piece of tubing, that warps the piece, but if I blob down 7018 like there's no tomorrow, it laughs it off.

    I think that I may end up having to clamp the piece and then heat it, which will be terribly awkward, but I guess I'll have to find a way.

  4. #4
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    Default Re: Bending tube with a TIG torch

    Just a thought? Could you utilize a Pipe Bender like Electricians use? I mean for the initial bend. Perhaps, also for reversing the process? I'm only attempting to help. Best wishes.
    The PUPIL who does not surpass his Master, fails his Master.

  5. #5
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    Default Re: Bending tube with a TIG torch

    Quote Originally Posted by creekbend View Post
    Just a thought? Could you utilize a Pipe Bender like Electricians use? I mean for the initial bend. Perhaps, also for reversing the process? I'm only attempting to help. Best wishes.
    I don't know whether that would work. I'm just trying to correct warpage here, not actually create a bend. I'm also not sure that pipe benders can handle square tube.

  6. #6
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    Default Re: Bending tube with a TIG torch

    Here's a photo of the piece, if you're curious.

    Bending tube with a TIG torch-2013-06-07-00.49.31.jpg

  7. #7
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    What if I was to clamp the piece at the ends, with a fulcrum under the joint, then bend it back to straight and remelt the joints with the torch? Leave it clamped until it cooled.

    It was heating the top side of the tube that warped it. Heating the bottom side is one way to bend it back, but it seems like if the metal was hot on top, it would loosen up again and be susceptible to clamping. Or would putting more heat into the joint just make things worse once I removed the clamps?

  8. #8
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    Default Re: Bending tube with a TIG torch

    I would think heat is heat. Never used a Tig torch before. Always used O&A torch. Since switching to propane I've leaned I don't like propane for heat shrinking material as much as acetylene. Here are some different examples of how I would heat shrink a T-joint. If you can heat these areas red hot, and use a spray bottle of water to cool the heated zone. The material must be cool to the touch before re-heating. Remember if you can feel heat with your hand, the material is still moving!
    Attached Thumbnails Attached Thumbnails Bending tube with a TIG torch-weld-2-1st.jpg   Bending tube with a TIG torch-weld-2-2nd.jpg   Bending tube with a TIG torch-weld-2.jpg  


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  9. #9
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    Josh: you need to heat a small area quickly without heating the surounding area. That will make the heated area have no where to go but up. Then as it cools it will pull in the surounding area. Lots of heat, short time.
    Dan H.

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    Default Re: Bending tube with a TIG torch

    Quote Originally Posted by CNC Dan View Post
    Josh: you need to heat a small area quickly without heating the surounding area. That will make the heated area have no where to go but up. Then as it cools it will pull in the surounding area. Lots of heat, short time.
    So, what I was doing was using maybe 80-100 amps and washing over a large area to make it red, but now I think that may be more of an approach that would be used for making the metal malleable for bending, but not for inducing anti-warpage like I want to do. Based on what you're saying, I'm thinking, if I was going to use a TIG torch, I would want to set it to max output (160 amps in my case) and use the finger-switch to hit the metal with quick bursts of heat--perhaps moving over the corners behind the joint, like in Shield Arc's example.

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