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View Full Version : Flame straightening, how to?



Fiero Addiction
03-24-2008, 05:57 PM
I just finished welding up a cutting table made of 4" x 2", 14 ga rectanglular steel tubing, approximately 60" square, with the 4" side of the tubing vertical. I managed to keep it straight and square while welding it. Then I welded sheetmetal on the bottom to form a tank to hold water. The tubing is now bowed up, I haven't put a straightedge on it yet, but it looks like it could be as much as 1/4" in 60". I know it can be straightened by heating the top with a torch, but can someone tell me the exact process?

Jon

Geof
03-24-2008, 06:16 PM
I have done flame straightening on shafts but never successfully on tubes.

The procedure is that you quickly heat a small area on the outside of the bend, and then quench it rapidly with water to cause localized shrinkage pulling the bend back.

An alternat method you can try, which I have used even though it is a bit hokey, is to simply run weld beads on the ooposite side of the tube to the ones holding the sheetmetal on. The idea is to balance the weld shrinkage on each side.

Fiero Addiction
03-25-2008, 02:51 PM
Is there a specific pattern I should use when heating? Circles, lines, vees?

Also, do I just have one shot at it, or can I do it as many times as needed?

Jon

Geof
03-25-2008, 03:15 PM
For straightening shafts I just used a small circle. The idea is to heat a small area quickly, then cool it very quickly.

Thinking about it a bit possibly on a tube a narrow line across would work better than just a small circle.

You should experiment on a length of tube to see just how much effect you can get.

Fiero Addiction
03-26-2008, 06:45 PM
Well I gave it a shot. I did a couple pieces of 1/4" plate first, heated them on the back side in the same line as the weld that bent them, then dunked them in water. They straightened right out. For the tubing I heated lines about 2" at a time lengthwise on the side opposite the welds. It worked really well. It took 6 to 8 times spaced out over the length of each 60" tube.

Thanks for the help.

Geof
03-26-2008, 06:58 PM
.... It worked really well....

This kind of thing is very satisfying. I know it sounds corny, but this is one reason I spend time on CNCzone. I think sometimes I can be of help to someone.