I am learning how to weld. I have a wire-feed arc welder (fcaw), 125 amp max. I am working with 1/8" plain steel.

My general technique isn't great but I'm working on it. My focus now is I am trying to figure out how to weld right angle corners while taking into account how the metal flexes as it cools. I haven't yet wrapped my head around how the metal moves.

As an experiment, I made two 90 degree corners. On one corner I did the inside first, on the other, I did the outside first. On both I went in opposite directions on the inside vs. the outside. After doing the inside/outside I immediately did the other side without waiting too long.

First I clamped the metal at 90 degrees and verified:

enter image description here

Next I tacked both sides in the center and confirmed again:

enter image description here

Then I did the welds and let both pieces air cool for a while until they were about ambient temperature (yeah, the spatter and the broken wire... working on it):

enter image description here

Then I cleaned it up with a brush wheel and checked the angles again. Both bent inwards:

enter image description here

The inside-first one warped significantly more, but neither of them turned out at 90 degrees. I expected the outside-first one to bend outwards but it didn't (one thing I should have done in this experiment is measured the angles after doing one side to see if the second side pulled it in the other direction).

One of the things this applies to is, I tried to weld four pieces into a square yesterday, and it came out more diamond shaped because I did the two opposite corners first and they warped inwards.

So my question is: What's the technique here? How can I weld precise 90 degree corners while taking into account how the metal moves? Can I prevent the movement somehow, perhaps do the welds in a different order? Some other trick? Am I welding too hot, maybe (there's a lot of spatter and some visible dig on the edges, but I don't know if this is a sign of a problem)?

  • 2
    @isherwood Oh... yeah... I wasn't really sure. Three attempts at a metal working site never pulled through on Area 51. Can we pretend that I'm fixing something in the house or like, building a fence or something?
    – Jason C
    Nov 17, 2016 at 17:31
  • 1
    I usually bevel the edge and tack everything. It may help to tack all 8 points of the corners then the metal can still be adjusted. After tacking in place run a short center bead on all 4 corners. after that if everything is still square you could finish out the welds alternating corners so it doesn't get two hot. Corner tacks and a center weld will be quite strong. If you bevel the outside corner you should be able to turn down the amperage and have less heat distortion and the problem with digging at the corner shown in the last photo before the before and after photos.
    – Ed Beal
    Nov 17, 2016 at 20:05
  • 1
    @isherwood I think we agreed some time ago, that welding questions were on topic. As long as they ask about the use and maintenance of a welder, or welding techniques, there's no problem.
    – Tester101
    Nov 18, 2016 at 11:20
  • @JasonC This question seems on topic to me. You're asking a specific question about how to weld, what you're welding doesn't seem important.
    – Tester101
    Nov 18, 2016 at 11:22

1 Answer 1


Most work I've seen like this where it needs to be precise employs 2 techniques.

The first of which is a welding Jig, complete with braces, clamps and the like to forcefully hold everything in position. Most of the time this uses a large, heavy welding tables with holes and slots to bolt the braces and jig too. C-Clamps and whatnot are helpful as well.

Additionally, it's not uncommon even after a well produced weld, to check for true and use a torch and tools to relieve the stress, while tweaking the alignment.

TL:DR - Keep it from warping in the first place, but if/when it warps, heat to adjust and de-stress as needed.

Also, it does look like you're welding a bit hot in places. Practice, practice, practice. There's nothing wrong with grinding out your weld, and starting over, or using a REALLY big wrench/hammer/pliers to straighten it out.

  • I've invested in a couple of proper welding corner clamps. There's some awesome welding tables with clamping systems out there but they're so expensive. Wish I could justify it. I think the clamps will help a lot. Thanks.
    – Jason C
    Nov 18, 2016 at 5:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.