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Hi guys ... just looking for some confirmation. The issue is plug welding 50 year old sheet metal to new panels. From what I've learned online, the best method is to drill the holes in the new metal, assuming same thickness. For mismatched thickness situations, drill the holes in the thicker metal. Correct? Thanks
 

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Hi guys ... just looking for some confirmation. The issue is plug welding 50 year old sheet metal to new panels. From what I've learned online, the best method is to drill the holes in the new metal, assuming same thickness. For mismatched thickness situations, drill the holes in the thicker metal. Correct? Thanks
I do it the other way, drill the holes in the thinner gauge, weld to the thicker gauge, you're less likely to burn through the thicker metal. Just my 2 cents.
 

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Brian Martin,Freelance adviser
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Absolutely, you want to drill or punch the hole in the thinner metal so the thicker metal is at the bottom of your plug weld. If you search the forum for "Basics of Basics" I have posted a lot of articles on body work. This is one on how to remove those spot welds when pulling the pieces off. "Basics of Basics" Spot welds, removing welded...

There are other random threads like this one, nice video on a plug weld. Plug weld Video

Here is a good one with some info on Plug welds. Plug welds

A basic welding post, print it out and read it a few times. "Basic of Basics" Welding - How do I repair...

Brian
 
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Rod...from a Chrysler?
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Plug welds depend on application, no? If I had a thin panel and had to weld a thicker one to it and no access to the thinner one, the holes would be in the thicker piece.
If you're worried about thickness and blow thru, back it up with copper or aluminum.
 

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This is what I do with repair panels welded not at the stitch welds.

I drill holes 1/2 to 2" back on both the old and new panels. I place the old and new panels flush. Then I use a backing piece(often cut from the old material) to weld the two panels to at the holes. Then I stitch weld the two flush panels. You need to make sure you let the metal cool and move around so you do not warp the metal.
The final result is a flush panel that can be smoothed out easily and is much harder to burn through. If done correct the repair will not be noticable and no filler will be needed.

You are adding more material and you will have a backing plate that might be seen(usually not as its on the inside). But you do not have a step. This takes longer as you need to cut out the backing piece which might be curved or have a roll.

If your making the repair at the old spot welds then yes you (almost) always melt into the thick and walk the puddle over/into the thin. This may have your dimes going right to left instead of left to right depending on whats thicker/your welding direction.

I always keep a fender, rocker, or something else around of diffrent thicknesses in my scrap pile. Gauge it then burn through on some scrap adjusting settings and feel before moving on to the stuff you spent cash on.
 

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Hi guys ... just looking for some confirmation. The issue is plug welding 50 year old sheet metal to new panels. From what I've learned online, the best method is to drill the holes in the new metal, assuming same thickness. For mismatched thickness situations, drill the holes in the thicker metal. Correct? Thanks
Correct. What this does is to keep the heat of the heavier material otherwise the thin metal would potentially burn back into a much bigger hole than needed in turn creating a mess to clean up.
 

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I generally butt weld patch panels And slick both sides. And only do rosette weld at pinch weld spots. The aftermarket panels are usually thicker than the origional for one reason or other. Start the weld on the thicker, and work toward the thinner. With a good mig, set properly, it happens very quickly, no time to lollygag around. just pop pop pop and it's tacked in three spots. then continue making pops about 2 inches or more apart, then come back and pop some more, untill you have a continuous weld. Grind flush, and prime.
 
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