Distorted pipe when welded

[danley]

Embarked on a project to build some side steps/rock sliders for my 4wd.
It was a fairly involved job but I was glad to finally finish the fabrication side of it yesterday only to find that the welding had distorted the 43mm x 3.2mm pipe on the inside rail(bowed about 4mm away from u bracket)enough to make fitting them quite a bit harder than when they were just tacked. Looking at the pics is this because the short pipes at right angle to the main rail were not directly opposed to eachother creating uneven heat? If I am able to get these close to opposite eachother should I weld half of one then half the other side to counteract the bending?Any comments would be greatly appreciated.
Thanks
Dan
I know it's already rusty, test fitted them last night and it poured rain, nothin like rain on bright steel.

 

[pedrobedro]

I wouldn't worry about it, if they are being used they are going to get bent anyway Personally I would have made the brackets and fitted them then made the sliders and tacked them to the brackets on the car. It looks like the bend on the inside rail has been caused by the weld contracting and pulling them in, how tight a fit were the spacer pieces ?

 

[KTMMICK]

The best way to sought the problem is to heat the opposite side of where you have welded until red hot and allow it to cool.

 

[danley]

Thanks for the replies fellas.
Love your work pedro
That was pretty much how i put them together, the 2 rails tacked together with the spacers (they weren't tight at all, was able to move them quite easily into position). Next bolted the u brackets to the chassis and set the rails up where i wanted them to sit then fitted legs back to chassis bracket and tacked it all together, was all sweet at this point. Then after welding all joints up they went bananas, literally.
Looking to do some for my neighbor so don't want the same thing happening, figure i try to get the opposing joints closer together to counteract the bending.
Seeing i don't have an oxy set i put a half piece of pipe around the otherside today and gave that some good heat with the settings way up, scrap turned red and hoped this would transfer into the work piece, still looks pretty bad, definately needs oxy for that kind of heat i think.
Thanks again
Dan

 

[Welderpaul]

Welding on one side only of a piece of steel section will always have a tendancy to bow it in towards the side of the welds. This is made worse by the relativly thin wall of the tube. Changing the location of the welds won't have much effect - it will still bend.
The best way to avoid it is to clamp the long tube against something solid, even with a slight prebend in the opposite direction (washers or spacer strip in the middle of the length of tube before clamping). Do the welding, then let it cool before releasing the clamps. There is a bit of an art in knowing how much to prebend by to result in a straight tube after welding.

 

[Bsmith]

Distortion by welds contracting is so annoying, would'nt help much with your project but if welding on long lengths, support them below where you are to weld so the ends hang down and weld on top.

 

[KTMMICK]

I dont have oxy either and have had this problem myself once and I got over mine by welding the tube on the other side and grinding the weld back.......painful but it worked!

 

[danley]

Thanks,
Will give that a go, it's become very frustrating trying to get it back
Dan

 

[danley]

I dont have oxy either and have had this problem myself once and I got over mine by welding the tube on the other side and grinding the weld back.......painful but it worked!

Well I gave it a go and bingo it worked!!!!!!
A bit strange though, one pulled back about half the distance, so still about 1.5mm out in the brackets(i can live with that) and the other one went past by about 2mm, I pulled it back before it cooled and now its straight.
No matter what I tried with the first one I couldn't get anymore out of it???
But like you say I've now got a fair job grinding it back, might invest in oxy gear if I ever have to do something like this again.
Thanks for your help
Dan