Metalwork Question- Door Skins

[MitchaPaLoOza88]

My door bottoms were all rusted out so I've been rebuilding them. At the final stages of fitting the lower skin over the lower door frame. I have a process question,

 

1. Should I weld the skin as is like in the photo and then try to wrap the edges?

 

Or

 

2. Should I pre bend the edges then try to fit up and weld?

 

[TobyB]

I would brake the fold first.

it's going to take some work to make it 180,

and you'll then need to 

work the distortion out.

 

How I'd do it,

 

t

[Highnote1]

I agree. Bend and shape and Get the fit great, then tack it on...slowly to avoid warpage that will show up like crazy on that flat surface. 

[TobyB]

Oh, it's gonna warp, no way around THAT!

 

But with tacking and shrinking and hammer and dolly and annealing and patience, you can minimize/fix most of it...

 

t

 

[MitchaPaLoOza88]

Ok, thanks guys.

[Tdh]

Hey Mitchapalooza,

 

Do you mind if I ask what setup you’re using to weld the sheet metal, and whether or not you’ve done this type of work before?   If you’re new to this I’ll be glad to toss in my 2 cents.  If you’re and old hand at this I’ll shut my mouth. 

[Simeon]

When I did the corners on my doors, I used the same clamps you have to secure and set the panels at the same height. This sets the slight curve (in my case) top to bottom and side to side. I then marked the steel and set out the flange to be turned over. Cut the patches out, turned the flange over to 90 degrees. I then reclamped in position and the welded across the face (spaced out stitch welds, leaving time to cool - If I could have reached in with a dolly, I would have planished the welds as I went). When completed, I then finished the flange with a hammer and dolly. 

 

If I was doing a long seam as you are, I would actually plug weld a strip of steel under the joint which the patch panel would be lapped over and the plug welded to. Less chance of burning through, keeps the panels co-planar better with less warping (from welding and grinding the welds). 

 

This is assuming that I could get to the lap welded section from the rear to allow it to be properly sealed with seam sealant or even glass fibre resin. I would also use weld through primer as you don’t want this to turn into a rust trap. 

 

 Bad diagram 

 

[MitchaPaLoOza88]

Hey Mitchapalooza,
 
Do you mind if I ask what setup you’re using to weld the sheet metal, and whether or not you’ve done this type of work before?   If you’re new to this I’ll be glad to toss in my 2 cents.  If you’re and old hand at this I’ll shut my mouth. 

Feel free, I'm still rather green. I'll soak in any knowledge passed down. First door skin repair.

Running a Hobart 140 on C25 Argon with .024 wire

[Highnote1]

Another option like the last post above that is easier is getting a flange tool like this. This creates the flange on the door as seen above and prevents burn through. I went with this on my quarter and it was awesome. Butt weld the ends that you can’t flange and that is it. Again, you have to be able to seal from the back. I am using this tool as much as I can when I can seal both sides from moisture. Way easier ms the cutting does not have to be so perfect like butt welding. 

 

https://m.harborfreight.com/air-punch-flange-tool-1110.html?utm_referrer=direct%2Fnot provided

[TobyB]

Just 'cause I done it a buncha ways-

 

the backing plate works, but then you have a backing plate back there.  It's a trap for crap, including welding slag, etc.

It DOES give you a lot more metal to weld to, and if you're bad at burn- through, it's a lot easier to get a good bead.

If you're careful with shrinkage and work slowly at maintaining the door curvature, it adds a LOT of structure to

a panel that's super- floppy when cut, and not particularly stable when whole.

 

The flange works, too.  If BMW steel was lower- tensile, you could flange the door in, tuck the plate over, and have less of 

a crap trap.  Its HARD to flange the stock steel, so for this, your replacement is probably softer and thicker, so flange that.

Flanging will distort the edge, and again, working the repair part will be easier than working the remains of the door skin.

 

Eventually, I came back to doing butt joints, as you (Mitch) show in the original pic.  Because the doors are so thin and 'brittle'

there's almost no way (for us mere mortals- true metalworkers can) for us to prevent some warpage.  If there's a thickness

to the joint, it'll lock the waver into itself, AND then it's almost impossible to anneal, shrink, stretch, and hammer and dolly.

There's this lump of a seam you have to work around, and it's just a pain.  I learnt this on Datsun Roadster rear quarters, which are

2 halves spotted together under the trim line.  They're hell to work on, and 25 years on, that's the ONLY place corrosion has popped up.

 

But it's all trade- offs.  If you're excellent at flanging, by all means do it that way. If the strip's your way, that's the winner.

 Butt welding's easy to get wrong- and hard to fix when you do.  But it's easier to hide your mistakes!

 

what I've learned by doing it wrong,

t

 

Edited July 11, 2018 by TobyB
Whole. Not Courtney's one- time band...

[Tdh]

2 hours ago, MitchaPaLoOza88 said:

 

Feel free, I'm still rather green. I'll soak in any knowledge passed down. First door skin repair.

Running a Hobart 140 on C25 Argon with .024 wire

 

I'll agree with everything TobyB just posted and add this...

The flanging or backing method will also end up causing rust issues.  This is a door, and water will get in there (windows).  

 

Also, that flanging tool will distort the panel and you'll have to deal with that along with it just being less complex to deal with butt welding the joint (provided you fit everything up nicely and CLEAN CLEAN CLEAN the metal).  

 

I'm sure you know this, but go slow and don't overheat the panel.  Move around a lot and take your time.  If you're at all nervous about this, practice on a couple of pieces of scrap.  Weld them up, then practice flattening them out.  I do most of my hammer and dolly work on the weld itself before dressing it down when I'm flattening things out.  Also, don't freak out if its not perfect.  Building primer is your fiend.  

 

 

[Tdh]

52 minutes ago, TobyB said:

 

 

what I've learned by doing it wrong,

t

 

Man, 

ain't that the truth...Seems to be the only way I learn anything. 

[TobyB]

Quote

  I do most of my hammer and dolly work on the weld itself before dressing it down when I'm flattening things out. 

  Oh, yes, this, for sure.   And don't be afraid to rough- grind the welds a bit, as you go, just to see how you're doing.

 

t

 

[Simeon]

This one is as about as hard a butt weld as you will ever see. Definitely agree with all the points about a lap weld being a rust trap but then a wide wide skim of filler to get the wave out of a panel like that is potentially problematic too (depending upon how it is done). 

 

I figure that if you put some care into prep and the products used to seal it, the joint will be at least as good, if not better than some of the other welded flanges on the car that have been there 40 years. All these things are compromises, these days you could use a flange / backing plate with body panel adhesive to achieve the same goal (some may say better - mainly the makers of adhesive). Once it is all buttoned up and painted over, what’s under there is between you and your maker until it comes bubbling up in 4 or 40 years. 

[MitchaPaLoOza88]

Ya this is gonna be a fun one. I pre-bent up all the edges on the large Pexto Brake at work today, gonna try and start it tonight if I can. I wish I did a better job with remembering to take pictures, but this door was a rusty fun one for sure. I will have to post some finished progress photos after.

 

I am gonna go with the butt welding the joint. I can fit a dolly and hammer on pretty much the whole seam, and personally I like doing butt welds. The Hobart may not be the best welder in the world but I've gotten pretty comfortable behind it and I don't find myself blowing through on good clean metal.

 

Backing the weld would make the job faster but I am more afraid of future rust. Also I feel like plug welds work the best when you are able to get a good clamp on the overlapping metals. I can see how I can clamp up the first half but when I would be welding the two final pieces together I would need some pretty long necked clamps to hold it together (or maybe like clecos)