Beginning to close off the rear of the sill area now. The B-post has been altered to make for a nice fit, and has been offered up using self-tappers to hold it in place.
As supplied there is too much flange where the outer wing attaches, and the overall shape is too curved. With the good loan door hung, and lining up with the outer sill, the temporarily mounted b-post could be marked off of the door and altered. It's now all drilled ready for plug welding to the repaired rear inner wing.
Next stage was to make the new front of the outer rear wing, the original having been removed as it was rotton, and access was needed for the kidney bowl, inner wing and sill repairs. This was beaten from 20SWG sheet, which is one gauge (more or less) thicker than original:
This was then scribed into the outer wing, cut carefully, and tacked into place:
This is a butt join, and it needs to be a good enough fit that you can't see light through it. The TIG is then used for tacking: the metal is heated either side of the join, which expands it enough to press the two sides of the joint hard together. The TIG arc is then swung to the centre of the join, and two parts melted together: no filler wire is used at all.
This continues all of the way down the panel, until the whole lot is tacked together. Then the joint is hammer and dollied to make sure everything is nice and aligned. Finally the TIG arc is fired at the top of the join, and slowly dropped all of the way down, in one continuous seam: again no filler wire:
The final stage is to 'tap-up': where the now very pliable joint (unlike a MIG-welded one) can be planished smooth with a hammer and dolly. This is where any ripples are flippered out, and the general shape beaten to follow the curve of the wing, plus it's a chance to do some fettling to the door gap (hammer and dolly again) to get it as close as poss. The great thing about a TIG welded butt joint is that you usually don't have to do much / any grinding, unlike with MIG welds.
After that is done the B-post can be finally welded in, and the base of the outer wing welded to the outer sill.
BTW, Sometimes people use a lap joint for this wing repair. In the coachbuilding industry, this is considered pretty much unacceptable as it can trap moisture / rust, and more to the point, leaves a hard line through the wing. When any filler or high-build primer is applied and flatted off, this hard line flexes less than the rest of the panel. As a result, the join sometimes shows up in the paint as a very slight dip, where more filler / primer has been removed as a result of the localised stiffness. Not always the case, but worth keeping in mind if this repair is needed.