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S-Curve in Square tubing.

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Hey all,
Here is a dilema that will be coming up for me this spring. I have a customer that has a sunken patio that is seperated from the yard by a low retaining wall that has a gentle s-curve to it. They want to further separate the patio from the yard and create and outdoor "room" by putting up a "screen" at the top of the wall. The design they want includes one inch box tubing for the frame. How do I create an s-curve in box tubing without collapsing or crinkling or crimping the walls of the tubing.

My Idea: My initial idea is to notch/slit the box tube through three sides at 1-2 inch intervals. This would leave one side wholly intact. Then I would bend the tube on a wooden frame, clamp it down, weld in the slits/notches and grind smooth. I am not sure whether it would be better to have the solid side on the inside or the outside of the curve, but my initial thought is to have the solid wall on the inside to avoid having to make large and awkward shaped notches.

Anybody ever done this? Any thoughts or observations that I have missed? I would try it out, but to get a good idea of the final curve of the product I need a fairly long piece, and I hate wasting a good chunk of steel when I can do some planning and info gathering first.

-Aaron @ the SCF

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Sq tube is rather easy to bend in the small sizes. All it takes is a simple section of a die as shown with a center rib to start the inside part of the bend pushing in, and some kind of restriction to keep it from bulging.

bottom drawing shows what it will look like after bending, Look at any of the commercially available things, outdor play equip atcera and you will see what I mean.


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at are shop we make a templet out of cardboard then we have a pyrimad roller that we sent the lenth thought and when its close we use an arbor press to fine tune the curve, with the s we make a mark in the center and send the lenth though half way then flip it and send it thought that other way. cutting and welding is a lot of grinding/ polishing.

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What size tube are you talking about?
What sort of radius/radii?
You say that it will be a long piece of tube...
...that leads me to believe that this will have a large radius.
If that's the case then a rolling mill, taking more than a single pass would likely do the trick...
I have a cheap, Chinese version, but it wouldn't be difficult to make one either.
You could likely, though I haven't tried it yet...fill with dry sand, weld caps on end (but don't seal, or leave/drill a hole to prevent pressurization) heat in forge or with large torch and bend to shape. You likely don't need thick wall for this job...that's good.

Let us know your process and the results, will you?


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I have had success bending 1" square tubing for the bottoms of corral panels by using a flat bar wider than the tubing shaped to the curve as my jig. I also found that heating the bar farther than the curve reduced kinking. It did dimple in on the inside of the curve though, if I remember correctly.

As for packed sand, I've never used it but would be cautious of a possible explosion or cracking if the sand expands. If somebody has used it, feel free to correct me though, I'm just expressing concerns over safety.

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I guess notching it would work Ive done lots of bends like that with wood.Its
called kerf bending-
Maybe cut with a hot saw through 3 sides and try this:

Make a cut with your saw and clamp it by the cut
Mark off a line equal to the raidus -from the kerf and rise the free end of the workpiece from the bench top until the kerf is closed. Measure the gap between ( the end of the line you drawn "equal to the length of raidus" and the bench)
This will give you the space between kerfs for a smooth bend

Ive never tried it with steel works with wood
might give it a try

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The Curves are very long and gentle and have a very wide radius. My primary concern with using a roller is that because the tube is hollow it would cause some amount of buckling in the tubing which would make for some interesting alignment problems when I attached the "mesh" of the panel to the frame.

Overall the top and bottoms of the frame will probably take a full 20' length of tubing. The mesh of the screen is going to be diagonally crossed 3/8 round. As I mentioned above, my fear was that a roller would cause buckling which in turn would create another angle to worry about when attaching the round stock.
Because of the length I want to do as little heating as possible (moving around a twenty foot length of steel with a heated section in my shop might become interesting at best ,as my shop is THAT large).

Has anyone had any experience rolling anything around 1" square tubing?

What I am seeing now is a ring roller (which has been on my to do list for a while) incorporating some sort of die system like Irnsrgn suggested to keep the top and bottom flat. Seems like I could turn out a die like that simply enough on the little lathe. (If i have to sacrifice and have one dimpled side so be it). Hm... Rolling a twenty foot length in my shop might also become interesting...

Please keep any ideas comming. This is helping immensely
Thanks all,
-Aaron @ the SCF

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Jeremy K,
Thanks for the info. Those are nice looking rollers. I am probably looking at something consisting of some plate, a couple pieces of axle, some kind of pressure screw or hydraulic jack assembly, a big chunk of channel iron, and maybe a few sprockets and chains (depending on how I decide to drive it). Same idea, just a little...okay a lot... more primitive and it'll probably take me a few more passes to get the curve. Thanks.
-Aaron @ the SCF

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