EnigmaT120, as you requested here is what I had to say about welding in patch panels. This information is offensive to some people because it conveys the clear message that bondo is for plastering, not for auto body restoration.
"Dave, welding the extremely thin sheet metal that is used in body panels is something that should be practiced on scraps before any actual body panels are welded. I have done a lot of it on my '36 pickup with oxy-acetylene equipment in the 70's because I did not have tig then.
Welding body metal causes tremendous warping and controlling that warping is the challenge. It cannot be totally eliminated, just minimized. Warping that remains when the welding is complete is removed by metal straightening and shrinking.
The welding steps are as follows:
1.Trim the pieces to be welded to a perfect fit for butt welding.
2. Place wet towels on both sides of the area to be welded to keep the panels cool outside of the weld area.
3. Make MANY very small tack welds along the seam at about 1 inch intervals. After each tack weld, cool the area with the towels.
4.Even with this many tack welds the actual weld will warp and will have to be done in short sections of a couple of inches. After welding each short section cool the weld and the whole panel.
5. When the weld is complete it will be worked with a hammer and dolly to remove the waves and irregularaties.
6. Then the whole panel will probably require work with hammers and correctly shaped dollies to restore the correct contour.
7. There will probably be some expansion of the panel that can only be removed by metal shrinking. That is a tricky procedure that I can only explain by actually demonstrating it or by making a series of sketches. I have no computer skills so I can only send the sketches on regular email after I get my wife to scan them.
What I have described above is, like so many skills, simple once you know how. But, like learning tig welding, a lot of practice is required and the first attempts are a real mess."
