I will never butt weld sheet metal again

After reading several posts here about how butt welding patch panels is better than lap welding I decided to try it on my latest project. What a PIA and waste of time. I've been doing body work for many years and have always lap welded panels. I know, the argument is lap welds are a place for rust to start. Well, after blowing throw my seams numerous times I have a hundred little barbs of welding wire sticking through the inside of the panel that I can't get to. This is going to form a good potential for rust, just as much if not more than lap welds. I have vehicles on the road for the last 20 years that are holding up very well.

Unless you have all the time in the world, or get paid by the hour, butt welding is the biggest waste of time, IMO. I will never do it again. In the time it's taken me to install 4-5 pieces I could have had all of my patches lap welded in and moved on to the body work.

Just a heads up for guys who are starting their first builds. Lap welding panels is a lot easier, faster and less frustrating.

Let the flaming begin.

 

Overlapping is the absolute wrong way to do it and butt welding is the only quality way to do it. if you overlap then you are wasting your time because you are doing nothing but inviting rust back into you panels for the future. Take the time to learn to butt weld an do it right or stop doing metal work. Theres no in between. It's a skill, you can learn it. No quality body men or fabrication shops that I've seen will overlap panels, it's just a cheap shortcut for under-skilled fabricators.

Consider yourself flamed.

 

I have done both,,the only time I will lap weld if everything has been sandblasted and is clean sheet metal,,of course it's always best to have clean sheet metal whether you lap or butt weld. HRP

 

Well I would say if you have vehicles on the road for over 20 years and still holding up that there is not a thing wrong with doing lap welding. I can understand what you said to about all the barbs of wire sticking through to the other side when you tried to butt weld. Different strokes for different folks I say......

 

I'm not a body man and am not taking sides about which is best. But I wonder how many seams are lapped and spot welded from the factory.

 

I have never lap welded a panel except when I had to do it in tech school to pass a test. I won't do it on my own or any customers cars ever. Technically a good weld seam should always be sand blasted both before and after being welded from BOTH sides but it usually doesn't happen that way in the real world.

 

There wouldn't be enough money on this planet to pay me TO lap weld a repair panel! How in hell are you going to stretch or shink that kinda mess to suit what ever shape it needs to be in? Butt welding is simple as hell whether your doing it MIG, TIG, or my current favorite gas hammer welding. I could care less about rust, it's just the craftsmanly way to do things!

 

All of them

 

I lap weld floors and and stuff like factory would do unless im patching in a section and that will get butt welded. Any type of body skin that shows and will be hammer welded. A butt weld is the only way to go......

 

Its funny you bring this up, I am in the process of butt welding a bunch of patches on my 55 olds. So far I have warped the shit out of a couple, but getting better as I learn to take my time more. It takes a huge amount of time to keep it flat (most guys including myself dont have the patience) but those who do can reap the benefits of minimal body work to do afterwards. You can easily spend a whole day welding 1 small patch taking your time enough not to warp the holy hell of out the panel.

I do not believe lapping the panels is "the wrong way" or "lesser quality", granted it is DONE PROPERLY and steps are taken to seal the backside and prevent moisture getting it. I can understand completely your frustration, I will probably look into lapping my patches in from now on.

Sent from my DROID device using the TJJ mobile app

 

Wonder why factory seams tend to rust out?

I personally was taught the mentality that when doing fabrication, bodywork, painting, or pretty much anything on a car that if your end results weren't better than factory then you are doing a shit job unless you are doing factory accurate restoration, which is cool to look at but very pointless in my opinion.

 

Why would 'all those barbs' pose a rust issue? They have no way to trap moisture.

 

I gas weld and that eliminates the barbs.

 

Well,I guess I'm just a cheap short-cutting under-skilled fabricating hack according to such a great craftsman as your self! HRP

 

I want to agree with the OP. I did some butt weld patches on my project and its a lot of time-consuming work.

As far as lapping; just knowing there's an extra thickness of metal on top would kill me though, I love to sand as much filler off as possible.

Perhaps if I used one of those panel flanger tools I'd be into it. Something to ponder.

 

That's OK - really it is.
they invented flangers and lap welds for guys that can't butt weld- not because its better. You are obviously not alone in this.

Now for those interested in doing it correctly there's some skill involved. Proper panel forming is paramount. Cutting and prepping the joint but only after knowing where to locate it, you see a dolly needs to be able to be placed there. Then there's the welding process - itself lots of practice required.

If this was your first ever sheet metal butt weld I'd try more practice first. Then I'd discover all the cutting tricks and tips. Because if its setup and done right Stevie Wonder and Ray Charles can cut a perfectly matched line on panel and patch.

 

Can't you 'glass the seam of a lap weld, thus preventing rust??

 

The problem I'm having is not warpage. All the panels seem to be pretty straight. I am taking the time to space my spot welds and letting them cool. Just like when I lap weld I start at about 2" apart and then go about putting welds in between the spot welds until I have a solid weld. I wire brush the welds then check for spaces. I think I have a solid weld until I grind the weld and I can see very small holes between some of the welds. I then try to fill those small holes and thats when I start blowing through, creating bigger holes which I then have to weld shut which just grow as I weld. I do finally close them up but it's really frustrating. I put a light behind the panel if I can before grinding and I am able to see if I have any gaps. If I see any I spot weld them shut. I doing a dog leg on the car and can't get a light behind to check for gaps because it's a closed area. I do see the minute holes as I'm grinding.

 

I but weld almost everything except where a lap on a factory seam is. To do a panel properly the fit is very important. Then tack and hammer the tacks to stretch them out as you go. When the tacks are an inch apart weld the seam fully. Mig welding creates hard spots that don't hammer and dolly well. I tig the open areas and mig the spot welds. Jim

 

Use smaller wire so you can get the heat down enough not to blow thru panel.

 

You said it, not me.

 

It will crack in the end. Fiberglass expands 8x more than sheet metal. 1/8 of an inch of bondo max or you didn't do it right.

 

Sounds like you had too big of a gap or the heat too high. When I butt weld all you can see on the inside is the weld that has penetrated through, can't even see the what was left of the seam.

 

Well for one thing a slight overlap on a car that is not exposed to salt and bad weather most of it's life will last a very long time. It's basicly a fair weather car so don't worry about it unless you building a show piece. I like to butt weld my stuff where it counts. It takes longer to do the fitting but the end result is you don't have that ugly seam bulging and have to smash down because it's higher than everything else. If your going to overlap, just overlap it by a hair say 1/16 or so. No need to have a anymore hanging down inside. If you can't get at the seam on the inside later to clean it, just oil it after the car is painted.

 

No SMART ASS,I just repeated your assessment of peoples work you don't agree with! ,I amazes me you come off as the end all be all professional hot shot but never post any this great work you do!

We know you are good at selling stuff in the classifieds but lets see some of your work! HRP

 

You need to make sure your panel gap is correct. If you are not TIG or Oxy welding then you MUST leave a gap(approximately the thickness of the wire you are using). If you don't have a gap when MIG welding, you WILL run into shit when it comes time to weld and will end up with warpage that will not want to shrink out. If you are having problems with blowthru or the sight of the barbs bothers you, get a section of copper tubing, hammer it flat and place it behind the seam. Weld won't stick to it. Also when filling in between your gaps, push the weld into the seam, don't pull it. Learn how to use your machine and it will do what you tell it to do. It's all in the technique...

 

well said

 

I used to have that frustration of blowing through the metal. Then I watched an experienced fabricator do it with MIG and noticed he held the torch as close to horizontal as he could and still get a decent tack. He said to use the thinnest wire you could get by with like .023 and turn the heat down. .035 is too thick and requires more heat to make the weld thus adding to the burn through and leaving more to grind off. So take the half hour to change your wire and if necessary your hose liner. My butt welds on 18-20 ga. have improved remarkably from those couple of bits of knowledge. I use a Lincoln 215 but it will turn down to a low enough heat and feed rate to make me look better than I really am.

 

Lapped panels are thicker at the lap then butted pannels so they expand and contract at different rates. You almost always will see the seam after paint, or at least a dip or wobble or something. Can seem smooth when its cold out, but when its hot out it will show, or the other way around.

 

...agreed with holding the gun at an extreme angle. The amount of build up is greatly reduced and the penetration is superior