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how to weld it perpendicular?


May 22, 2006
This is a question about welding distortion. Say I have a length of 1/2" square bar two feet long and I want to weld it solidly to a piece of flat bar lying on a horizontal table so that my bar winds up perpendicular to the flat. If I just take a welding magnet and stand it straight up and then tack it on the side away from the magnet. The weld will pull the square bar out of vertical. Now if I remove the magnet and tack the other side, it won't pull all the way back if any.

An old guy once told me to don't stand it straight up. Tilt it 2 degrees away from the first weld. Then don't tack it, weld the other side. The weld should pull the stick just about straight up. And with one side fully welded, it won't move when you weld the other side. After that, it won't move when you weld the other 2 sides because it's now solidly welded on 2 sides.

Only thing is, he told me that in the early '70s and I have little faith that I remember the procedure right.

So what do you think?

I do it all the the time, just not with any accurate dimension. Mark 1 eyeball only. but, yes.
I used to tell my crew at my last job that only 2 things are GUARANTEED to happen to every single weld...1- it's gonna get hot. 2- it's gonna warp, so plan ahead!
Tack both ends then tack sides. “Hot setting” second line tacks is cool trick. Instead of having weld pull material you beat it - not peen- while it is red heat to push material out. It is back and forth with using weld to try and pull back into square, or pull with setting.
Plug welding is also another underused option. It pulls parts tight together- so perpendicular is warp state.
leaning a part and using the weld to pull it straight has been done for ages but theres no hard rule that says 2* will always work as theres many different variables. try 2* and if it over pulls lean it more. doesnt pull enough then lean it less. simple trial and error.
it will also pull on the perpendicular side to the weld depending which direction of travel you weld. youll have to take that into account as well.
when welding you need a plan A ,B and C
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One more factor to consider is the flat bar after welding, it won’t be flat anymore so what is perpendicular?
Not really enough info in your post, is the square bar 2” long or 2’ long? Is the flat bar 1/4 x 4 or 3/4” x 6”?
In some situations you can restrain the material to keep it in position, in other cases it can’t be restrained so you have to live with the distortion or correct it after welding.
Good luck.
I rock the part just enough to open a slight gap on one corner. I tack where the gap is. Then I lean the part the other way just past square and tack an adjacent corner. Then I lean the part just past square in the remaining direction and tack it. Check square and hammer if necessary, then get the last tack and you are good to weld and are square in all dimensions. You'll get a feel for what gap you need (maybe 0.02-0.04 if your cuts are square) and how much to angle it past square (away from the direction the tacks will pull). I don't have to worry about further distortion because in everything I make the other end is connected to structure (I'm never welding perfectly square spikes) so no extra care is required beyond alternating sides when welding.

My boss and I were prefabbing stilts for a cabin in a snowy area one weekend, and he was tacking as I was going along placing and squaring tubes. It took us maybe 10 seconds per column to get it all tacked perfectly square and in the right spot, and we were being very careful to get those columns as perfect as possible.

Consider when welding that you likely have one direction that is going to be more critical in terms of angle than others. Do the welds perpendicular to the critical dimension first.
One more factor to consider is the flat bar after welding, it won’t be flat anymore so what is perpendicular?
Not really enough info in your post, is the square bar 2” long or 2’ long? Is the flat bar 1/4 x 4 or 3/4” x 6”?

The vagueness kind of goes with a thought experiment. Sorry about that.
How ambidextrous are you? Got 2 MIG machines? Tack the 2 opposite sides at the same time, gun in each hand. I did that a few weeks ago. For sure it is not so easy to watch 2 puddles. The part geometry was such that I could see a puddle with each eye, brain did not process the images as well as I hoped.
Most of what I do gets clamped to one of the massive welding tables I have. Pay attention up square or rectangle mechanical tubing. Clamp it up square and never tack a butt end to a radiused edge. Tack where butt end meets flat surface and complete those welds first. It takes more wire/bigger puddle to weld radius corner to butt edge. More shrinkage.
The best thing you can do in your situation (flat bar with a tube leg in center) Is to not weld across the flat bar. So you only weld the sides in the direction of the flat bar. The fillet welds that would go across the flat will pull and be way more noticeable than the side welds will.
If you want to tilt the tube so it will pull into square then a test weld is in order, hold the part sq with a magnet etc and weld it & let it pull, note the angle of how much it pulls. Then tilt your tubes that amount and you should be really close.
I used to put a piece of shim stock between the two, tack weld two corners, remove the shim, tack other two corners, then weld all the way around. I found that this kept the cross piece from warping quite as much and the gap kept the two square.