Since this is a thread on patch panel advice, I’ll add some constructive criticism/pointers that will hopefully explain what’s going on. So don’t feel I’m picking on your work, as you’ve done very well for a first attempt. Better than my first attempt, I would add. But some thoughts and observations that may help out on the next patch, or for the next person.
You look to have a low just under the top horizontal weld, or at the top of the patch. There are a couple schools of thought in panel fitment, the tight butt joint that you show, and the slight gap. Pro’s and con’s of each:
Tight butt joint:
For welding, MIG dot welds shrink more than any continuous weld as you are getting a circumferential shrink around each one. When you weld, there is a slight swelling as the immediate area heats up and you may see some deformity as the metal tries to push outward from the weld. Then, as it cools, the metal will shrink up tighter than it was previously. This is why it’s important to planish after each and every weld dot while it’s isolated, it both applies stretch to the slight shrink that occurs and allows you to bump any deformity back to a “flat” panel. Having tight butt joints minimizes the chance of the two panels pulling together and losing the crown of the panel. ie: it’s easier to planish and add the slight stretch needed for the shrinking that’s occurred, and to bump the panel flat again from any deformity, than if we had to planish and make up for crown loss from panel pull. My inclination of what you have there is that the patch pushed slightly downward as the weld heat caused it to stretch outward, and the planishing/bumping failed to bring the panel flat again while those weld dots were still isolated. This means that the next weld as it expands will have a tendency to continue the trend of pushing the panel downward, as once it has started and without correction, it now becomes the path of least resistance. Hence the long area of depression next to the weld. This also suggests that the upper weld seam was done last, as the other welds would have locked the panel from moving. This slight bit of distortion you may see in a tight butt joint is the downside of this method, but it does a better job a maintaining the crown of the panel, advantageous for someone that prefers less filler in the repair.
Gapped butt joints
I think the standard gap I have heard used is one wire diameter thickness or less, with the thought that your weld dot will still be able to touch metal on both sides and not turn the inside of the panel into a porcupine. But invariably, as much as we try perfection is a lofty goal and you’ll see some wide joints (especially if the opposite weld has already pulled the panels together) that we do have occasion that weld wire protrudes through before making electrical contact to initiate the weld process. So having this slight gap does give the metal a cushion for expansion that you may see less weld distortion, but it will also allow the two panels to pull together more that you lose the crown in the panel, especially in a low crown area. This would now require much more planishing to restore the crown of the panel than had we used a tight butt joint. So where you had a nice tight butt joint all around to start (especially for an “island” patch), all of the metal surrounding your patch is respectively flat. Had you used a gap surrounding an island patch, you would have much more pulling of the surrounding metal that you would have seen puckers surrounding your patch. So good job there.
So invariably it appears this low was caused by this being the last side welded/tacked and that the planishing that was done failed to bring that one area back to flat when individual weld dots were being planished. And
@JimKueneman, for a guy that claims to not be a metalworker, is spot on in his assessment. Seldom does a rust hole (if that’s what this was) occur well above the bottom of a panel and not affect what lies beneath. This would have been an opportune moment to cut the left vertical seam all the way downward, and the upper horizontal seam all the way across, to make a patch of the entire bottom corner. This eliminates two weld seams, and with it two areas of shrinking, planishing, and finishing. Bend your flanges around and now you only had two welds instead of four. And can rest easy that you’ve inspected that bottom corner for any rust issues. For door to fender/quarter gaps, the other downside to a weld so close to the edge of a door skin is that any shrinking may pull the edge inward where your door gaps just widened. Here’s a fender repair that shows that exact defect: (post #93 if it doesn’t link correctly)
Yep, its a '67 long fleet with a 300 horse 350ci small block, up here in sunny lancashire. Lots around here, I borrowed some workshop space from some friends to do that work, it shared space with the following: Genuine 68 427SS Impala Nova being built for the track 9 second 1/4 Camaro...
www.garagejournal.com
So something to keep in mind that a test fit may be in order to make sure door gaps are consistent before you get too far along in the paint process.
Overall, job well done for your first time. That low area, providing you have free access to the back side, can be bumped outward using a dulled chisel, a chisel ended body hammer, or any number of tools that would bump it outward. Lay your panel upside down on a shot bag (or other means of support) and lightly tap the depression outward from the back side. Less is more in this case, light taps to sneak up on the finish line. For as small as the area is, I would prefer using a hammer lightly tapped into a dulled chisel or similar over swinging a chiseled hammer and missing.
