metalwork help-

OK Helpers, I have a problem and I need a fix besides cut off the roof and start over. In chopping the top on my 50 I cut relief slots in my roof so when I reshaped it it would have the right curve and not oil-can. Now that I'm welding them up they are pulling the curve out of the roof and leaving me with flat spots. I'm using a mig (use what ya got,right) and just dropping dots, not beads like normal. The metal is staying pretty cool, I can touch it with a bare hand after 15-20 seconds. It just seems to be shrinking the roof tighter and tighter. So my question is how to fix it? Would heating the weld with a rosebud and working it with a hammer and dolly work or turn it into a wavy mess? Just use a big hammer and hope for the best? bury it in mud cause its hopeless? Thanks for any thoughts-

 

Every time you pull the stinger you are shrinking the metal.The blue area around the weld(haz)is were the metal shrunk.You need to re-stretch it as you go.

On the areas you have already welded,stretch the haz and it will come back around.

I have wrote about this several times,I think I showed how to do it in the Let's see some sheet metal shaping thread.

It does not matter if you stitch weld,or try and keep it cool you are shrinking the metal while welding.One way or another the weld will need to be re-stretched.

 

haz... heat affected zone?

this thread is useless without pics. no telling what you have going on.

I cut relief slots in my roof so when I reshaped it it would have the right curve and not oil-can.

not sure what that means.

there are many ways to chop a car. we have no way of knowing what you are doing.

I saw a 48 chevy once where the guy cut the roof in 2" strips like 4 feet long. I have no idea what he was thinking. for some problems there is no good fix

 

haz... heat affected zone?

Yes


And you are right pictures would help.

There are people that weld and cool the weld with a wet rag thinking that will help control the shrinking,it won't.

As soon as you sting it,you have put heat into the panel and the metal shrinks.

 

These guys are giving you good info. Every time you weld, when the weld has cooled the metal will have shrunk a bit. The cumulative shrinkage of the welds is pulling out the crown, or flattening the profile. The discolored area around the weld (heat affected zone) has to be hammered and stretched back into shape.
You can lessen the effect by using a series of spot or short welds, but you cannot eliminate the shrinkage. Get out the hammer and dolly- It'll make all the difference in the world. Good luck!

 

One other thing before you start hammering & dollie grind the proud part of the weld (high lump) down flush with the surrounding metal inside & out when ever possible. Do the grinding slowly you do not want to put a bunch more heat into it. You will be able to raise the shrink easer & smoother then Danny.

 

You'd need to grind the back side of the weld too - hopefully you are getting a bead protruding down too, otherwise you might want to make sure you are getting your weld hot enough to actually weld - not just sit on top.

The Mig weld bead is really hard and doesn't like being hammered. You can still adequately address the shrink by stretching the metal on either side.

Just another reason why you probably won't go back to MIG for sheetmetal once you've used TIG or gas - but that's a whole other debate, and like you said, you use what you got.

 

Thanks Guys, at least that gives me a good starting point. This is going to be one of those long nights you hate being a car guy- at least its warm here.

 

if you stretch one side of the steel, the other will follow. . . unless you mean either side of the weld, and not top/bottom of the steel

nothing wrong with a MIG weld. and yea you can get them to stretch back. the welds wont take a LOT of beating, but will take enough to allow you to hammer the welds

 

Hey gtostu,

Try this: Tack, hammer, tack, hammer etc. Whenever you're welding and the metal is getting outa shape, STOP! If you straighten the panel as you go, you control the shape throughout the whole process. Yeah, this may take ya alittle whyle to weld up your chop, but is much faster than chasing damage you created with too much heat, in a localized area that could have been avoided!

A rosebud torchtip is a great tool for plate, pipe & frame work, but has no place in sheetmetal repair.

Swankey Devils C.C.
" Meanwhyle, back aboard The Tainted Pork"

 

I agree wholeheartedly.

I think a lot of guys get discouraged because when they're welding things up, they get a little distortion, and instead of stopping and fixing it, they forge ahead and end up trapping that distortion with their subsequent welds.

If the panel moves, stop and move it back. If you weld it while it's in the wrong place, you'll fight it and fight it, and never get it entirely straight.

Also, if you stretch every weld right when you make it, you always know which weld caused the problem. Takes a lot of the guesswork and irritation out of the process.

There are old timers that say you can tack every half in and then just weld the whole panel up in one shot, but unless you've got the same number of years under your belt as they do, you're more than likely going to end up with a warped up mess and no idea how to get it back into shape.

 

Rosebud to heat, absolutely not! Weld about an inch or inch and a half ( weld should penetrate, not just lay on surface) then hammer and dolly (heat if neccessary). This pic is an example of the process and shows the amount of heat distribution needed.

 

That is why the "better" sheet metal guys use a curved formed panel to fill in where the stock metal doesn't have the correct contours....you have MUCH less welding than welding up a bunch of slits!
So...if you really need to learn how to do hammerwelding, correcting shrunken weld seams, you're getting in pretty deep into sheet metal forming. My suggestion, since you sincerely seem to want to do it right, is to do a quick search on "tuck shrinking", since I don't think you have an English wheel, and practice! In a relatively short time, if you try hard, you'll get the hang of it.
Than go back and make new compound curve panels to replace the "frankensteined" parts of the roof, and have a minimun of weld seams, hammering, and filler work!

 

Hey gtostu,

When you geta chance shoot us some photos of your project. Don't feel like Neil Armstrong, everyone of us has at one time or another been weldin on a roof or quarter or some other low crowned panel only to ask ourselves WTF did I do , here?

Proficiency comes from experience, sometimes bad experience!

Swankey Devils C.C.
" Spending a nation into generational debt is not an act of compassion"

 

Good Advise here.

The shrink comes from the weld its self

The HAZ is stressed not shrunk

Hammer the welds as you go & most or all of the shrink can be reversed.

Go slow

Practice

Fit up as close to perfect as you can get

And watch your results