MD
I very much do NOT agree with your suggestion for use of MIG welding. That would be the last option. steel body fabricators would only consider GAS or TIG as options. Of the two TIG would produce less heat, but leaves the weld harder than the parent metal around it, which makes it more difficult to work the new panel after welding. I am GAS welding everything in the traditional methods of bodywork. Every seam is fitted to within 1/16" as a butt. The panals are than tacked every couple of inches and hammer and dollied while red. The hamering shrinks the weld and keeps things as they were aligned. I then weld only aboit an inch at a time, continuing with the hamer welding process. A little here, a little there and things work out fine. I'm using a 000 welding tip. Pressures at the regulators are 4 pounds each, and I do not use any filler rod. The majot problem with MIG is that way too much metal is deposited, and it is not possible to flatten it out, resulting in grinding, warpage etc... Using the methods I've described I do a little pick and file work and the job's done. I accept no more than a 1/16" of body filler on top of my work. So, that's my long response to yours. Folks- I would really NOT recommend MIG as a process for this kind of work. Don't get me wrong, what I do is not easy and takes some time to learn, but it is one of two correct ways to do this sort of work. As for the idea of modern panel adhesives, they work very well where an over-lap situation occurs. For instance a patch panel for the lower section of a TR3 front fender would be ideal. I've done this in another situation. I create about a 1/2" 'step' along the edge of one piece, offset enough that the other piece will lie flush into the step. The panel adhesive is applied, and when set, the bond is amazing! None of this is possible with this project however, as everything is a butt joint.
TR3MOD