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  • Twisting square tubing

    Any one have any success (deliberatly ) twisting square tubing with uniform results, such as you see with some square wrought iron railings?

    Ken

  • #2
    Ken, twisted quite a lot of rod in my blacksmithing exploits, but I had never tried square tubing. I'm assuming you're talking pretty large cross section, else it is easier just to use the rod. I've done 1/2" or so, but for tubing, I'd assume you're looking at 1" or larger.

    Gonna take some elbow grease, leverage, and heat!

    Cheers,

    BW
    ---------------------------------------------------

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    • #3
      Iv seen a twister before... http://www.metalcraftmachinery.com/M...ster/index.htm these guys sell one. Also got some nice pics of underclothed women playing the game twister for my effort in finding that pic in google search, so all is good.
      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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      • #4
        Bob,
        Largest would be 1 1/4" in 12 Gauge.

        Rats, don't like the heat idea, too difficult to get uniform results I would think.

        Just a nice smooth uniform twist, would not have to be even a complete turn, just something to give some aesthetic form.

        I have access to an old and large lathe that I was thinking on using with a plug and 4 jaw chuck with some form of tail end support for the square tube. Years ago I saw an old gentleman use one for twisting solid square bar stock. In back gear you can fall asleep waiting for a full revolution.

        Would be nice if it was an easy setup for a test run.


        Ken

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        • #5
          Originally posted by Black_Moons
          Iv seen a twister before... http://www.metalcraftmachinery.com/M...ster/index.htm these guys sell one. Also got some nice pics of underclothed women playing the game twister for my effort in finding that pic in google search, so all is good.
          BM,
          That appears to be for solid bar .

          Thanks
          Ken

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          • #6
            Evan?

            Evan has a terrific very strong, long and rigid power-driven twisting machine that he used for square section steel bar.

            I don't know if he used it for square tube.

            My guess is that he will read this thread/post and reply.

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            • #7
              Originally posted by oldtiffie
              Evan has a terrific very strong, long and rigid power-driven twisting machine that he used for square section steel bar.

              I don't know if he used it for square tube.

              My guess is that he will read this thread/post and reply.
              Well, it's been an hour

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              • #8
                I have done it- with my twisting machine, which is mondo.
                Its a Hebo, made in Germany, 3 or 4 hp motor geared down to about 10rpm, incredible torque, and it has an electric brake so you can stop on a degree. Any degree.
                http://www.usahebo.com/
                The trick is that there is a tiny moment, when the square tube twists, but before it collapses. This is why you need the CNC control my machine has, and the control down to one degree increments.

                Otherwise, it just collapses in on itself if you go too far, and its pretty much impossible to Un-collapse.

                I have done even bigger stuff hot- I have an arbor in my yard whose posts are 3" square, 1/8" wall- we heated up about a foot with a rosebud, then used a big homemade wrench, with one end in a vise that is bolted to the floor.

                The short answer is- if it was easy, everybody would be doing it.
                The machine, twisting a small square solid bar.



                Twisted solid 1" square-


                And a piece of 2" round tubing, twisted, showing the collapse- square does this pretty easily.

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                • #9
                  Twisting square bar.

                  An old guy that made ornamental iron type burglar bars and decorations here had a Rigid pipe threader mounted on a rail and he twisted 1/2" bar. Doubt that would work on tubing. I broke the gears in my Rigid pipe threader the cost of repair was aprox $400. Also saw a hand powered version where the "hand wheel was the wheel off of an old farm implement. It was not in operation but appeared to use the same technique the old man did in that one end was fixed and the other end slid through a square die. The old man had a counter to count the number of revolutions turned.
                  Byron Boucher
                  Burnet, TX

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                  • #10
                    Ries,

                    Actually looking at your picture, some controlled collapse can look pretty good.

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                    • #11
                      Is there a tendency for the tubing to collapse at each end right next to where the twister grips it?

                      Roger
                      Any products mentioned in my posts have been endorsed by their manufacturer.

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                      • #12
                        It's nearly impossible to twist hollow tube sucessfully. The reason is how the twisting is regulated. When a piece of bar is twisted it strain hardens with essentially zero strain at the neutral axis and maximum strain at the outer fiber. The distribution of strain is kept even by the material itself in a solid bar. As any particular portion experiences slightly more strain than the rest it becomes slightly harder to twist so the strain is taken up by the weaker areas. This automatically distributes the strain equally throughout the length of the section.

                        With a hollow section the section winds up and some parts may become closer to the neutral axis than the rest. As a result those parts are easier to wind as the torque available depends on the twisting radius. This leads to a runaway condition that causes that section to absorb all the strain and collapse. Better results can be had by twisting angle iron which will wind up evenly until it forms a hollow square tube. This was something entirely unexpected that I found when playing with my twister. While my twister isn't CNC it is powered and I have very good control of the power via a belt type slip clutch.

                        This is angle iron twisted until it closes ( the piece standing up).

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                        • #13
                          Originally posted by Evan
                          Better results can be had by twisting angle iron which will wind up evenly until it forms a hollow square tube. This was something entirely unexpected that I found when playing with my twister.

                          This is angle iron twisted until it closes ( the piece standing up).
                          That is very interesting and unexpected !

                          EDIT:
                          Evan, is there a way to calculate the shrink rate?

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                          • #14
                            If you mean shrinkage in length, it isn't allowed to. The starting length and the finished length are the same.
                            Free software for calculating bolt circles and similar: Click Here

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                            • #15
                              I would tend to think you'd have to keep a lot of tension on it while twisting. I don't know how much that would help prevent random collapsing of the tube, but I'd think the tension would have to be high.

                              A quick thought that came to mind is to surround the square tubing with a close fitting round tube while doing the twisting. Still, I don't think that would prevent random collapsing of the square tube, though it would probably help.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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