I checked my past projects to see what I had done in welding panels together at a 90. This was about all I had. Note how tightly the joints are trimmed. With working on the bottom of your quarter, especially if welding up-side down, you'll want the joint as tight as you can get to reduce the possibility of blowing holes......
Noticed this damage while cleaning up the rear window channel today, hoping to get a step closer to primer.
The first step I normally take is to use the pick to check the surrounding area for any hidden damage, and decide how far to take the opening. Once you find solid metal, the next consideration is the ease of dressing out the repair. It's easier to grind and sand on an outside radius than an inside one, so that is factored into the cut size. Sometimes you don't have a choice, but best to make it easier on yourself when you can!
The channel is actually made in two pieces. The spot welds in the pinch weld area are removed from the top layer to remove the damaged pieces. The vertical piece actually travels down beyond the bottom of the window in this case, so that will be installed first. A new piece is cut out and bent to fit, and final sanding/grinding to get a tight weld joint.
Notice that the outside corner where I had cut vertically actually has a slight radius to the bend. Had I merely butted a straight patch up against the old, it would have pulled in from where it should be located, resulting in the absolute need for filler. So a bend was added to the patch during fabrication, then trimmed most of it off to match what was there prior, for a no-filler patch..
The bottom piece has a radius in two directions, slopes up and in.
The outer radius was hammer formed after the shrinking and stretching was done. Then trimmed to fit and welded in place.