Up the Crack or Down?

[CaddmannQ]

I have a 1/8” pressed steel shape that has a 1” long crack at an edge. I have drilled a hole at the end of the crack. Now I am going to weld it up.

Should I weld towards the hole, or towards the edge?

This is mild steel and I am going to use the TIG welder.

[Ironman]

I would control warpage by backstitching

[CaddmannQ]

Thank you Ironman.

I won’t try to weld it in a single pass, but I guess I asked the wrong question.

Would you put the first puddle near the edge, or at the hole, or perhaps somewhere in-between?

Since I did not know the best place to start this weld I was going to start in the middle of the crack and jump back-and-forth.

I have total access to weld this from both sides flat on the table.

[astronut]

I would start the weld at the edge while the piece has not absorbed much heat yet. Less tendacy to melt the edge than if tried it last after absorbing a bunch of heat and wanting to melt the edges away.

[digr]

I don't think it really matters.

[CaddmannQ]

It needs a little bit of straightening, and I will wait to do that until after the welding, but I doubt it will have too much warp.

Of course everything depends on my skills as a welder. All things considered, this first little bit of welding should be a breeze compared to what comes later.

But really, I was just curious if there was a general rule about welding up cracks where you have to drill a hole.

[Matt Shade]

For flat work on the table I don't think it matters a whole lot. Do whatever is easiest to work at in a comfortable position.

Other variables are more important like the thickness of the material and the position you are welding in etc.

With access to both sides and fairly thin metal if you were in the vertical position it would be ok to weld downhill.

With thicker metal or only having access to one side I would definitely run uphill if I couldn't lay it down flat.

If it is a large gap and the shape of the part is a tight tolerance I would tack a bridge of some sort across the crack if possible before welding it, or at least clamp the hell out of it because the shrinking weld can pull the crack closed and warp your part. Sometimes I will start at the open edge of the crack with some very cold tacks and just stack them until the gap is bridged, then go to the toe of the crack and weld back and burn through the tacks.

[CaddmannQ]

Well I ended up having to weld several other things first, so this crack business got delayed. With a little luck I will get it welded tomorrow.

I’ve been getting more practice with the TIG welder and I am a lot more confident about how well this will come out.

[CaddmannQ]

Just in case any of you are wondering what I finally decided to do,

I finally welded that crack today.

I clamped it down on the anvil to keep it straight, put a good tack weld at the edge, and worked back to the hole.

There was no problem with warpage. It came out straighter than before, which is what I had intended all along.

But I laid it on a little cold, so I back-gouged the weld (with a tiny Dremel Moto tool) and welded it from the back side as well.

Then I ground it out flush, filed it down neatly, hung it up in the air, and banged on it like a bell.

Sounded beautiful. No more cracks.

I clamped it down and hung my weight on it, and the whole rail flexed, but it did not crack. I was real happy about that.

[CaddmannQ]

Originally Posted by Matt Shade

. . . Sometimes I will start at the open edge of the crack with some very cold tacks and just stack them until the gap is bridged, then go to the toe of the crack and weld back and burn through the tacks.

Except that I welded from both sides this is what I ended up doing. I wasn’t trying to tack it quite as cold as I did, but it worked out great in the end.