Help! I've warped my roof skin

[Shox Dr]

I think the biggest mistake the OP did was to leave a gap. The peice should have fitted perfectly.

 

[minimutly]

I only weld two adjacent sides, deal with any shrinkage, then weld the other two. This halves the issue, but never gets rid of it.

 

[Onoff]

Ok I will give it a go, fingers crossed! Onof thats insane!!

See here:

Mk 1 3000GT CAPRI Restoration - Andys Auto Body

Our lastest epic project is this rare facelift Mk1 3000GT, built in the halewood plant in 1973 and fitted with the otional rallye pack, vinyl roof and cloth/vinyl seats. It arrived partially stripped with the vinyl removed and first impressions are that it has had a very dubious repaint and is...

www.andysautobody.co.uk

 

[dave h 2]

Oh dear.... I don't understand what I've done wrong? I didn't get it hot or weld for too long or put pressure on anywhere, the patch is the same thickness as the roof, I'm confused

Welding a flat plate on a compound curved roof doesn't help. Just using a grit blaster will mess up a roof.
I tack without moving the torch and bob about, one each on the sides so it takes forever to do a patch but it stays very cool.
Grind both sides flat, keep the heat out of it with a water spray (Detox sprayers are good)
Use a light hammer and tap lightly and often (steel is slow to move and it's all in the wrist action )

 

[minimutly]

Welding a flat plate on a compound curved roof doesn't help. Just using a grit blaster will mess up a roof.
I tack without moving the torch and bob about, one each on the sides so it takes forever to do a patch but it stays very cool.
Grind both sides flat, keep the heat out of it with a water spray (Detox sprayers are good)
Use a light hammer and tap lightly and often (steel is slow to move and it's all in the wrist action )

Battling tops....

 

[Torqu-E-Cycles]

I ground the welds down nice and flat whilst keeping it cool, tried to stretch it but my left hand with broken fingers wasn't up to it so cut it out slightly larger and the roof came back into perfect shape again!

Now, dare I try it again or do I make a plate a few mm larger and put it in underneath.... the roof will need a skim regardless so I think for the sake of my fingers and sanity I'll do that!

 

[qwakers]

panel bonding a piece in underneath is the safest option, for sure.

 

[Onoff]

Sunroof?

 

[Torqu-E-Cycles]

Panel bonding, is that a welding term or a type of glue haha?

 

[Torqu-E-Cycles]

I don't want a sunroof sadly!

 

[qwakers]

its glue.

https://www.3m.co.uk/3M/en_GB/p/d/b40066467/

 

[Onoff]

What about MIG brazing it?

 

[Torqu-E-Cycles]

Ooh I haven't heard of mig brazing before? I'll have a Google! Will look at panel bond too as I've also got another project on the go, a mini speedster, the roof needs cutting and widening and there's no chance I'm going to try welding that! It's going to have a removable back so won't be structural at all.

 

[Shedendman]

Judging from the photos,were you actually on the roof yourself while doing it,miles away from the patch itself looks sunk/stressed,plus(as far as i can see) your patch is flat,no where on any car roof is it flat.
Cut out the patch,and try and shape the roof how it should be,keep off it while welding the new patch in,not easy i know esp if its dead centre like,tac and cool,tac and cool,look at it like a clock,tac at 12,then 4,then 8,then 1,5,9,so on so on.
Dont knock panel bonding(agreed@qwakers ),in fact with the small patch/repair you have it would have been my 1st choice,filled over job done

 

[Burdekin]

The amount it distorted the first time I doubt you will keep it anywhere near flat however you weld it if you can’t plannish the weld. Big panels with minimal structure and shape are a challenge. Ideally you would Tig or oxy weld it in a little at a time and plannish as you go along.

 

[Torqu-E-Cycles]

3m panel bond is really expensive! Is there a cheaper alternative? I know 3m products are the bees knees but if there's something tried and tested for cheaper, as I will need a fair amount of it.

 

[octo0072000]

tiger seal or sikaflex are both PU glue

 

[Torqu-E-Cycles]

Not a solid bond though is it... can't have flex if filler is going on top of it

 

[sasquar]

as others have said, its the 'pull' from the welds shrinking that have caused the issue rather than the heat input itself. The way I tend to deal with it (i have some experience) is to make a plate that fits with a small gap all the way round (these days i would actually tig it with no gap, but as this is in the 'mig' section we'll go down this route...) then tack the corners. (You may want to grind these slightly at this point, you may not, depends on how everything is set up.) Then i would hammer and dolly each tack weld, checking the roof line at all times, youre looking (again, i appereciate other have mentioned this already) at just stretching out the tacks so that the plate is back in its 'neutral' position. Once this is done, and your happy that the roof is where it should be, i would do another set of tacks, halfway between the corners, and repeat. and repeat. and repeat.

Once youve got a good few tacks around it, chances are pretty good that it will start to stay where you want it, so each round of hammer and dolly work will be quicker than the last.....

Mig is a bugger to hammer and dolly at the best of times, so make sure to remove any excess weld, before you start each time, so that youre not trying to move more metal than you need to.....

Mig brazing is another option, same process, less heat input, less shrinkage and easier to hammer and dolly, but still a bit of a tease.

For now, i would cut just around the outside of your current weld, and that will almost certainly pop back into position.

 

[Morrisman]

Sunroof?

It will be if he cuts the patch out every time the weld shrinks.