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Getting butt welded sheet metal joints smooth

27K views 187 replies 18 participants last post by  farna 
#1 ·
Guys, I often view this forum when I need help with my fab projects. I decided to finally join. I have a problem that I have been unable to master. This has been going on for years. I can not get butt welded sheet metal panels smooth. I either have low, pits (shrinkage) around the welds as shown in the pics, or I grind too much away, get pin holes in the metal and then burn thru a lot when fixing the holes- showing how thin I've made the parent metal.

The part in these pics is a mini wheel tub that I am expanding further. I cut an aftermarket tub and added a slice to the inner rear section where I thought it became to tight for the tire.

I originally had the tub welded up and welds ground down. I used a flap disk to grind them flush with the parent metal and then used the edge of a 3" cut off wheel on a small die grinder to make the panel look smooth. Finally I finished with a quick go over with and 80 grit 2" sand disc to blend it all together. Then I hit the welded seams with a planishing hammer. There were tons of pin holes in and round the welds. I filled those, ground them flush with the parent metal, and the product at this point is what you see in the pictures.

Again, I have never been able to master this. How do you people get these patches to fit perfectly flush so you can't even see the weld seam? Is this the result of me using too much heat or having too big of gaps between my butt welded pieces.

This tub and projects from the past have always been under my car or hidden. I want to stretch my car's fenders and make wheel flared though, so I will need to know how to make perfect butt welded seams on an exterior body panel. I'm extremely frustrated.

I am not new to welding sheet metal and especially am not new to welding in general. I'm using a lincoln sp-255 220v wire welder with 75/25 and using .030 wire. .023 doesn't work worth a crap in this welder no matter what I do. I realize .023 is best for this type of stuff but I can not get it to function. I do have a miller syncrowave 200 TIG welder and did some of this welding with that (cutting perfect shaped patches to elliminate gap and be able to TIG from there is a whole nother subject and skill I need 2 master 2!!!)), but I had up to 5/16" gap in some places on this tube, so most of it was MIG'ed with the Lincoln. Please help!!!

j





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#5 ·
Thanks a lot for the suggestion. It couldn't come at a better time. My gas is out and I am going to get some this morning.

I would have a very, very hard time justifying getting another welder. If anything I think I will tell myself I need to pony up, start cutting patch panels with MUCH tighter, better gaps, and using my TIG welder. Why is it that these large welders can't do the thin gauges? Voltage and wire feeding settings are finite, actual numbers. These are not arbitrary setttings. In my mind these number should yield the same results when placed on any different machine platform. That doesn't seem to be the case though. Does anyone have any information on this?

I have been watching a few youtube videos on the subject of this thread. I believe the pictures I have posted here are a result of me welding too much in 1 area at a time which is yielding in the extreme shrinkage of the metal near the weld. Am I correct?

On my upcoming patches and panels I will weld much smaller tacks and hop all around the seams to reduce distortion. In the mean time, what is my best course of action to fix this piece without using bondo?

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#6 · (Edited)
You'd be better off with a 70/30 mix than using Co2 without a doubt.
If you do a lot of sheetmetal welding go with .020 wire and tips.
show some pics of the weld before you start grinding and we can be more help. my best guess is your trying to weld too cold. and yes, you cant just run a bead with sheetmetal, its tacked, spaced and tacked again. while your getting the hang of it try using a course hand file to cut down the weld. a good weld tack wont need but a few strokes with a hand file to be flush with the surface.
 
#7 · (Edited)
no gap fitup

gaps cause problems as the weld shrinks, and the back side of the metal has to be clean. I have some scraps of copper pipe I hammer and form for a back up . harbor freight also sells back up coppers. A friend teaches the panel fab street rod classes. here;s a link to an exercise he has his studenst do to practice a no gap fitup and minimum filler weld

lazze sells accurate alignment tabs you can use with cleco's to hold the panels so you can scribe, then weld Rod doc also has some good info on zero gap and no filler. It takes a lot of pracatice. My lincoln Square wave 255 tig has a pulser that can help preventing burn thru.
http://www.metalmeet.com/forum/showthread.php?t=6292&highlight=mindover
 
#10 ·
Thanks for the great videos timothale. Lazze has a lot of great vids. I haven't watched the 1 u posted.

What is the metal meet link u posted in ur 1st post? I can't open it because I'm not a member. I registered but now have to wait for a moderator to approve. What a cumbersome pain the ***** process. That's an old forum practice that metal meets should change if they wanna get more members, but I digress.

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#11 ·
zero gap tacks

to tack the zero gap panels, extend a sharp tungsten about 1/4 inch then slide the point across the panel with the cup on the panel until you feel the seam with your tungsten , then rock the torch sideways keeping the cup in contact with the panel and a small gap , then just a quick stomp on the pedal. I bought my tig used and it came with a water cooled torch with the thumb amperage control, good for some things but I had to get a new foot pedal for doing some things like these tacks.
 
#12 ·
Alright. I'll try that too.

In response to deadbodyman, I forgot To mention in my 1st reply to u that my welder doesn't work well with small wire. Idk why. Using .023 is not an option. There r a couple posts talking about this where I posed some questions concerning the topic. If u have any suggestions on that let me know.

Someone also mentioned welding too cold. I do NOT believe that to be the issue at all. The pictures may appear to be showing a large build up of material seen when welding cold, but the ground welds are flush with the parent metal. The unground areas around them are the pits and shrinkage in trying to fix. Yes they are extreme. That's why I'm here.


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#22 ·
Save your money drill screws are better in every way. and also easier to use and faster. theres no clearance troubles if you need to close a door or deck lid to check the gaps. I ran out and bought my first set after seeing Days of Thunder. I just had to have them and couldn't be talked out of it. Are you using a tig or mig? I suggest getting used to mig and getting the hang of welding and what a good weld looks like before wasting time and money with a tig You have to start at the beginning. Any welding coarse worth a dang will start you off with oxy/act then electric then mig and you wont even get to touch a tig until the second year.
You say your mig wont work well with 020 wire, look at the drive wheel and it should have two groves you have to turn it around so your using the groove marked 020. some of the better welders a few drive wheels including rubber ones for aluminum wire, yes, you can weld aluminum with a mig. What kind of mig are you using? I'd forget about trying to tig and stick with the mig until you get good at welding. anyone can get good at mig welding in a few months some a few weeks its the easiest way to get good welds. look into EZ gring wire, its softer and the welds are softer.
 
#14 ·
rod doc info

rod doc lists the various size tungstens and amperages he uses for various gages of sheetmetal. but every welder works a little different. another possibility of welding problems is old dirty or surface rust on your wire. I worked for a metal fab shop on the coast in california and the salt air mist blowing in every afternoon could cause problems. The shop had the ability to custom mix the gas from huge bulk tanks. and I remember one time they even had a small bit of hydrogen mixed in. I have no idea what it was suppose to do but they welded different parts with different alloy content.
 
#16 ·
What kind of Voltage and feed r u guys running for 18ga steel?

Guys, I appreciate all the information this far. Keep it coming. This is all great knowledge to have so as to avoid the situation I'm in on future welds. In the mean time I used my TIG welder for damage control. I set it to 60 amps and hut the welds. I drug them out further to make them lay in the shrunken spots. I think the lizard skin under body paint I plan to use will hide the welds now.


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#17 ·
I go by the door settings on my machine. the process is tack tack tack and then hammer hammer hammer. Repeat until the part is welded. then file the seam. If you have holes either you are too hot or you are lingering in a spot too long..

Sam
 
#19 ·
Cut the problem areas off and weld in a new piece.

If you want to repair a thin spot, take your TIG and hold it there for a brief moment and the micro metal will flow away until it gets to thicker metal.

Get that TIG machine out and practice. It's the best if you want nice invisible welds.

The third pic shows an area of poor tacking where one sheet is higher than the other. Each tack has been ground down with a zip disc to reveal this. It is then knocked up from the back with a hammer on dolly before welding with filler rod.

Rod Doc likes to fuse his material but I prefer adding filler so that it penetrates right thru leaving little gribnets on the back.
















 

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#20 ·
mig feed rollers ?

You said you were having trouble using smaller wire. If your feed rollers are worn you might need new rollers for the wire size and a new tip and mabe even a new liner.
There are a few new welders out there that can do pulse mig they would be ideal for us part time hobby welders but the prices are still too high for me. I have seen You tubes of guys using silicon bronze in their wire feed for body panels. I know oxy acety brazing must be sanded clean to avoid later paint problems.
 
#23 ·
You tubes of guys using silicon bronze in their wire feed for body panels. I know oxy acety brazing must be sanded clean to avoid later paint problems.
Watch out for you tube guys.
Those silicon bronze welds will crack for sure.
Only use this material if you want something to fill with.
It's very brittle and can't be worked with a dolly.

I haven't heard about the oxy/ace welding issue before.
Are you talking about the golden brazing rod? That should also not be used on body panels. A regular steel TIG rod can be used which is actually the best of all 3 methods. It's the least brittle.

(I didn't include arc welding as a method)


Pics below are of silicon bronze added after the pieces were already welded. I wanted some filler for a small corner radius.





 

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#24 ·
oxy acety braze body panels

When I worked at Ford they used gas welding on certain spots on the 65 and later mustangs, on the Quarter panel door opening where the fold for the character line and at the tail end of the quarter under the tail casting, the gas was a mix and they used a large tip and the blue flame cone was about an inch long, they had to keep up with the assembly line speed. Later down the line they used a wire wheel or a rag buffer that was dipped in glue then in abrasive, Usually the welds were smooth and they just needed to remove the glass flux. I still have about 10 pounds of the flux coated rod the guy that was working on the shut down team gave me when the factory closed . Anybody that still had their old ID card got into the big garage sale. I don't know the alloy but it is an easy flowing rod and is a golden color, and leaves a lot of glass flux on the weld. .
 
#25 · (Edited)
Don't get me wrong, theres no doubt tig welding is by far prettier and looks best of all methods and is what we should strive for BUT lets be real here what good is all that pretty when its under bondo and primer? Not only that but walk into ANY bodyshop and try to find a tig welder, it aint gonna happen, tigs are too slow and the learning curve too steep for most But you will find one or two or more migs at any given bodyshop. Trust me even a mig will be hard enough to learn without any welding experience or someone to show you how, and what good welds are supposed to look like. When it comes to weld beads, prettier isn't always better you need to know about penetration the root and proper surface and joint prep, you have to know what to look for if you want it right. Just because anyone can hook up a ground and pull the trigger on a mig and join two pieces of metal on the first try don't mean your ready to tear into a wrecked or rusted car and start replacing frame rails or sheetmetal but it is (by far) the easiest way to learn welding. Trust me when I say this if anyone is having trouble mig welding theres no way you'll be able to tig with success so have some fun playing with the tig then put it up on a shelf and get good at mig welding before you take it down again.
Arc welding is not an option when it comes to cars only thicker stuff but is a valuable part of the learning process at welding courses.
Although I've never been able to gas weld (steel rod) it is a good way to do sheetmetal on OLD cars but NEVER on newer cars with high carbon steel or high strength steel. I hope this helps you to know some of the "why's" about our welding answers and why they vary. Stick to mig welding for now, master it, and forget about the tig.
Think of it like this, if you cant lay down primer without getting runs everywhere and dry spots everywhere else, getting a nice paint gun wont help much, you need to learn gun control and the basics of how a gun works so when there is a problem you can take it apart and fix the problem. also you shouldn't think you can do better at painting until you've learned priming.
 
#26 ·
Wow. Very impressed with all the answers I'm getting here and how quickly they're coming. Different from a lot of other forums. I hope you guys chime in on all my future posts!!!

Anyway, forget the clecos and just use sheet metal screws? I need to cancel that order ASAP if that's what you're all recommending.

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#27 ·
That's what I recommend and use, self drilling metal screws, 1/4" head. 5.00 for a 100 at Lowes but you can get better quality and cheaper if you search around the internet. But you wont know how much better they are unless you've used the Clecos. I think I paid 100.00 for my first set of 20 or 30 with the plyers. Heck I probably DROP 20 screws every time I open a box.
Now go watch Days of Thunder and you see a car they are building with Clecos and its about the coolest thing you'll ever see, looks like a porkypine.
 
#31 ·
Mike, I'll have to disagree. Hobby guys are not in the auto body business.

My answers above are for the original post and the title of this thread.
Get the TIG out and start practicing so you can get smooth butt welded joints.

BTW, the most important part of using the TIG has nothing whatsoever to do with welding.
You will be forced to make your patch panels properly without gaps.
Even with MIG, you are toast if you have huge gaps.

Taking time with fitting panels nicely, no matter the welding type, will be time saved 10 fold.

Most guys rush this and end up paying for it in time wasted trying to get all those cracks and gaps filled. Then they need to work out the oil canning, etc....:drunk:
 
#32 ·
Most guys rush this and end up paying for it in time wasted trying to get all those cracks and gaps filled. Then they need to work out the oil canning, etc....:drunk:


Yup. I'm in the "most guys" and that's why I'm here. I've done patches before where I really thought I was meticulous and took my time, but the results were little better than what was shown here. I guess it's something I really, really, really need to practice. The patch fitment with zero gap seems unobtainable for me at the moment.




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#35 ·
I was self taught TIG welding at lunch time at work.
It's actually quite easy.

The reason I finish my welds as I do is because on stainless you cannot leave any divots.

The OP states he already has a TIG. A little shove may get him to dust it off and check it out.

If anyone ever has a question about it, I'm all ears and willing to offer the little bit of theory I know.

And of course, you're correct, fit, fit FIT!!!!!!!
Get them fitting nice and the welds will be better.
 
#44 ·
I went to tec school just to learn tig but had to basicly waste the first year doing oxy /act cutting and then arc followed by mig all of which I had been doing for the past 35 years theres things like keeping you tungsten sharp that are ez to learn but take forever to figure out without someone to show you. I cant imagine anyone who has never welded picking up a tig and welding without guidance. I know I couldn't have done it without my welding experience on other types of welding. heck I still cant gas weld with steel rod to save my life and I tried and tried I just cant do it. I had a body shop in Fla. that was in the back of a muffler shop and that's about all they did was gas weld he could weld the top side of a muffler pipe that he couldn't even see just as well as the bottom, I couldn't even gas weld a flat piece of steel on a table. some people have it, some don't. luckily there is no gas welding on cars and welding itself is just a small part of body and paint work.
The most valuable lesson I learned at welding school is I love to weld.....for about 10 min.. after that I pretty much hate it, it took 2 years of school to learn that. I'll never be a welder.
The problem I have with Tig is I cant weld a panel without warping it slightly so instead of warping panel after panel until I get good enough I just stick with the mig and can weld a patch dead center of a hood or roof with absolute Zero warpage and usually just a skim coat of finishing putty and primer finishes it up for paint.
Sorry for all the long posts but its been cold and raining for two days and I don't have anything better to do.:sweat:
 
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