Looking to see if anyone has tried to twist 2" thinwall square tubing. I have a project where I need to put a twist into about a three foot lengths of 2" square tube.
I'm thinking that if I insert a loose fitting round pipe inside the square tube and would then pack the tube with sand and weld caps on each end that this would stop the tubing from buckling. I have a large old pipe threader which I'm going to try and do this cold also since it is rather large of an area to try and heat up uniformly at once.
Any thoughts or other ideas and practical experience would be appreciated.
You'll need a LOT of torque!
I haven't twisted tube, just flat or massive square. The trick to use some tube to keep the thing straight is right. In your case, I'd put just some round inside of your square tube. No sand, no caps. If you weld on caps, you need much more force and the twist won't be even. You could also slip some round tube over your square tube if you haven't something that fits inside. Doesn't make a difference.
I would try it with just the pipe inside the square tubing first. If it works it will be a lot less work. And I think it will work.
And mebbe heat it up w/ a rosebud O/A tip. Sposedly yer not sposed to use rosebuds on B tanks, but if you have a flash suppressor in line, doing it on a full tank should be OK. I've done it. Or preheat some other way.
It will twist nicely if you keep it under tension. Doing that is a bit tricky. Find some 2-1/2" x .250" wall square tube, cut some 1/2" slices, weld these over the 2" tube. make a 3' long fixture out of 2 pieces of heavy wall 2" pipe (or similar strength) along with some end caps. You will need to shim the end caps to start the twisting with the tube held snugly. Putting enough torque on it is your problem!
I've done it with smaller thinwall steel by putting a bolt through holes in either end and mounting one set firmly to my work table, then taking the burner out of my forge and giving it a couple of passes with that, but it has a tendency to spiral at the same time. I think that if I were able to put it under tension as suggested above that that might not happen. You could probably wind up doing just as well by fitting a round pipe down the middle and putting the bolt through just beyond it. If it begins to scrape too much, heat the whole thing up and stretch it out a little, let it cool some and try again. Can't promise all that much for strength, but it would probably do for decorative work, which, since you haven't mentioned concerns about the seams weakening, I guess is what you're up to. Just dont heat
it too much, and turn slowly. GCC