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How to Know When to Fill or Patch a Gap When TIG Welding

A new TIG welder asks, "How do I know when my fitup is so bad I need to cut a patch rather than fill a gap when TIG welding?"

When you're welding a butt joint, you want your fitup to be really tight, a nice clean, even joint. Kevin shows some 1/8" cold rolled steel with a 1/16" gap. "You can get away with this," he says.

But when your gap is 1/8" or bigger, now you're pushing your luck. You can still fill it - Kevin says he's done it enough times - but now you have to think about whether it's structural or cosmetic.

Are you just trying to patch up a corner that has no weight on it? Or are you working on an I-beam that holds up half a building? These are things you are going to make your decision on.

That 16th of inch gap - which you can see as he shows a 1/16" filler rod - you can fill, no problem. You can use a 1/16" filler rod, although Kevin would probably use 3/32" rod just to make sure he has enough metal to fill the gap and touch either side of the base metal so he gets a good joint.

But when you have an 1/8" gap - which he shows with 1/8" filler rod - now you're going to have problems. You can end up with a weak joint, especially if you didn't do the welding with a backer behind it.

Kevin shows a piece of 1/4" copper plate that he uses as a backer to make sure he doesn't just weld right to his workbench when filling a gap. But if you're welding something up in the air and have a monster gap to fill, either cut a new piece of metal, or cut a patch and put it in.

And get it fit right so you can get a good joint. That's the only way you're going to be sure.

Just think: you're the one who is going to be standing under it. It's your life on the line if your weld fails.

Before you go, you might want to see him stick around and try to get an Oscar ....

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