The Stovebolt Site Forums The Shop Area Paint and Body Shop issue with mig welding sheet metal

I'm curious to see if I can find out what I did wrong on my weld job. My doors, 1953 half ton, were horribly rusted, so I bought inner and outer lower skins. I asked questions here, and watched lots of videos first. I installed the inners first, welded all of the way across the inside, plus across the ends. They turned out fine. My problem is with the outer skins. I clamped them at the ends, and installed a few leveling, gap setting clamps across the seam, so I had a gap all of the way across. I went slow on the welding, took lots of breaks, and moved around on the seam while welding, trying to only weld in the coolest area. I was generally happy with the look of the weld, and had good penetration. BUT, when I finished, I have a raised up, (ill call it puckered) area right at the seam of the weld. I'm sure that I did something wrong, but I have no idea what. Just trying to learn here, so it doesn't happen next time.

I use a flange tool (makes a countersunk lap seam on one piece) and Harris Stay-Brite solder and flux. It works quickly and the solder melts around 400~450 degrees so you don't have that warping and puckering. On things like doors, you can get everything like you want it, drill/rivet the panels, solder and then grind down the rivets and fill. That solder is as strong as you need and when you're done you shouldn't have much to grind/fill. There are several flange tools and some don't even cost $50. Harbor Freight has one for about $35 or so. Be sure to neutralize the flux with soda mixed in water or it will oxidize over time. If I have to do anything else, I'll use a brazing torch, but brazing must be done at a much higher temperature and a brazed joint won't be as strong as the Stay-Brite joint if you've done it correctly.

https://www.harrisproductsgroup.com/en/Products/Alloys/Soldering/Lead-Free-Solders/stay-brite.aspx

Read here...………… https://www.stovebolt.com/ubbthread...-tricks-for-sheet-metal.html#Post1023791


It doesn't sound like you did any planishing to stretch the weld. Any weld will shrink as it cools, from sheet metal to 1" thick plate. Your results are from skipping a step.

If "not planishing" was the reason, maybe could not get behind the weld with a dolly? Possibly could weld the outside repair first to be able to access back. I was also going to say that too tight of a gap/no gap can cause, but you say you used the blade style clamps which do leave a good gap.

We are not sure exactly what you have ended up with. May be fixable, may not. We would need several good, well lit, pics to see what you see. You may be describing warp and you may not. After we see pics, it may be possible to grind off weld and re slit and re do. If warped, you are screwed. I think you probably tried to go slow and tried to skip.

It seems like the remedy will be to grind off the backside welds, saving the piece to be reused. Then planish with reach-in dolly backer and see if "pucker" goes away. Depending on posting pics first.

Some say get as tight a gap as possible, some say leave a gap. The clamps you used generate about a .040 gap. This point is debatable. Some of the "tips" seen on the internet can conflict with each other.

Remember: Metal EXPANDS when heated. If gap is tight, it may "pucker". Metal SHRINKS when it cools. It may not, probably will not, flatten out the pucker. Even planishing may not. When the two "tectonic plates" collide, the mountains rise up at the joint or worse. So this is where the battle of the butt gap opinions begin. We are, of course, talking thin sheet metal. The correct gap is between zero and 1T.

Also, as Robert linked, it mentions NOT welding both ends of a panel first or NOT doing a perimeter first. This may trap the piece and not alow it to move. He seems to indicate to start at one side and move across. Did you do that? I see you clamped both ends first?

Many times I am unable to planish and have not had any bad things happen.
I see inner and outer door "bottoms". No skins. Can you post the vendor and part numbers for reference? Don't see an inner skin. I see there is an access cover inside bottom of door.
The inner turned out fine because it had some non flat features (ridges, raised/lowered ribs, dimples, changes in direction, etc). These will help eliminate warp. The outside is flat and smooth and long. Those welds are the most dangerous.

There was only a very small portion of the weld that could be accessed from the back for planishing. This would be through the inspection cover on the inside, down below. The inner skin isn't really what I'd call a skin, and your right, it has some breaks and angles in it that likely kept it from warping or stretching. I think that I bought the inner & outer from LMC, but will have to double check that. The reason I did the inner first is because of a youtube video that I watched in which the guy said that you always do the inside first. That sort of made sense to me because the outer has to fold over the inner flange and thus has to be positioned just so. Perhaps I should have done it in the opposite order though. The fitment might be a little more critical, but at least you could get to both sides of the weld. I do remember that I started my weld in the middle, and then worked back and forth from opposite ends toward the midde in order to try to keep it cool. I can't send pictures right now, because the weld area is covered over with body filler right now in an effort to fill in the low areas on each side of the weld and smooth the whole thing out. I don't yet know if that idea is going to work out or not. If it doesn't work out, I'll remove the bondo and then can take pictures. I'll stay on this, and will know in a few days. If worse comes to worse, I do have another pair of doors and their probably a little better than the ones that I used. I started with these because this is new to me and I figured if worse came to worse and I ruined them, then at least I would have ruined the worst pair. That might be foolish thinking, but that's what I thought. Thanks for the excellent reply. I'll check back in as work moves forward.

You are doing good work. Your thoughts and methods are right on. EVERYBODY has had those kind of problems and many other problems with thin metal. It is a welding area that is like no other. It is a learned art form. It takes awhile to develop your own methods that work for you. Suggestions and "tips" are guidelines only.
Example: Experienced welders and some well known books say no gap. I-CAR says must have a gap.

If I should have to start over, does planishing mig welds require a special hammer or dolly. I already have body hammers, ball pein hammers, brass hammers, etc. in many sizes. Are any of those satisfactory? I have a small number of common dollys too, but just cheap stuff. Like I said this sheet metal welding is new to me. Please forgive my dumb question.

Mike,
Door welding sucks. There is absolutely nothing supporting a vast expanse of nearly flat, thin sheet metal.
One thing which may add to your type of problem is the length of time spend creating each of the tiny little welds. A common error is have the power set too low, which requires one to keep the button pushed longer, making more heat. The little weld needs to be a quick buzz and you are done.
Have an air hose handy to blow air on the surrounding metal (not the weld) to stop the heat from migrating to the rest of the panel. Lightly tapping the surrounding metal (not the weld) will also stabilize the structure of the metal on a microscopic level. The molecules are in a state of flux when heated. The tapping helps stabilize this flux.

Interesting butt weld idea.

Wow, looking back on it, and knowing what I know now, that Eastwood tool would probably have eliminated my problem. I wonder though how well it would work on the old 16 gauge door metal. It's kinda thick stuff compared to what they use today. I've bought many things from Eastwood over the years, but I never noticed that tool. If I am forced to start over from scratch, I'll be trying one of those.

The skin would have been 19 ga. Other structures will be 16 ga, maybe floors, bed sides.......
Better check the web for reviews of that tool and the welding of a butt weld that way. I just posted it as "interesting".

I'll do a little research on the tool. Youre right though about it being interesting. Before I started my door welding, I checked the original and the new metals with a sheet metal gauge. Both checked 16 ga.

Every home builder thinks they need to metal-finish every panel. The fact is that even the top builders and restorers in the country use plenty of filler on their patch panels. I read a Street Rodder magazine article once the estimated that there were probably fewer than two dozen cars in the country that were totally metal finished.

Conclusion: knock the high spots down with a hammer, throw some bondo over it and don't sweat it.

Take those Eastwood "training" videos with a grain of salt. In many cases it's less about showing a proper way to do something and more about selling some gimmick tool. Looks like this is designed to make a valley of sorts so you still have a weld holding either side together. I feel this is going to have the same pitfalls as the flanged (lapped) repair that results in ghost lines showing in your final paint...





If you can practice with some scraps and get the welder setup to produce a full penetration weld, you don't need the gimmick tool..

I appreciate the replies from you guys and I will follow your advice. Getting back to work on these doors sometime today. Thanks

I like this article too, long to watch but worth it.

That was my thought after watching that. "Make your weld a touch hotter!"

"Intersting" indeed. I am "interested" in why no one informed this salesman that his "stress crack" was not a stress crack but was nothing more than lack of weld penetration. The high crown of the weld is the dead giveaway.

Well let me say this about that. He does not call it a stress crack. He is making a point that I made about butt weld gaps. Whether he intended to or not.
His point is that coats of filler, primer or paint will get cracked by this "unwelded" crack. The weld has been ground away.

So when I spoke of the battle of the gap as: some say zero, some say 1T or larger, this illustrates why a gap is necessary. The weld needs to "fill" a gap instead of piling on top. Penetration. If you leave a gap, when you grind, it will not leave a crack. In my experience, it's better to fill the gap and "penetrate" each edge than to try and "melt" the edges together in thin sheet metal. That's what TIG does. You don't even need a filler material in some cases with TIG.

Not to mention that a tight gap can cause deformation. Like I said, there are experts on both sides. Both have good results. The DIY builders can find their preferred way. There is not just one way.

Penetration in this sheet metal case really points out the fact that you are trying to get the filler material to join the base material. There is a fine line, in thin material, between good penetration and burn thru and distortion. That's why you have to zap-dot weld as Robert says. Contrary to the poster saying his case is 16 ga (.060 thick) material, many cases are 18 ga. (.048 thick). That is 20% less thick. 19 ga is hard to find, most suppliers sell even number gauge.

Thick plate is easier to do. No zap welding, lay into it with all you got. Burn thru is not an issue, heating the base enough is, undercutting is, penetration enough to meld thick metal to think metal is.

The aforementioned tool:
If someone credible reviews the tool, I might agree it's a break thru. That will take time. I would like to see the back side of that trench weld. It does have some merit. It is copying the chamfered edge used on thick plate. It will, however, be a different weld than a zap dot, I think?

NOW! The fishy part. They only show what type of weld they did for 6 seconds. The welds look like a spot weld of sorts or tacks, BUT the height shown is not tall enough to level grind as shown in the video. SO......what did they do? What kind of weld was it? Big spots? A bead? A stringer and weave? Don't know. That was not left out by accident. It's the oil part of snake oil....or in this case "Fishy Oil". That's going to have way more fill and way more heat than any other "butt weld" method.

Following this thread - it would be a valuable experience if some of us stovebolter’s were able to meet at someones place, and had an impromptu sheet metal welding get together?

It really is an art and science - with some good knowledge sharing and practice the skill can be passed on.

I give a lot of credit to those who are not afraid to jump in and learn.