Originally Posted by MARTINSR
By the looks of the first photo you didn't skip around at all, that is the problem and why you got warpage. Those welds shouldn't be next to one another like that, they need to be spread out, one at the front, one at the rear, let it cool, one in the middle then one at the rear, let them cool, one at the front then one 3/4 way, then let it cool one a foot back then one between the 3/4 and the rear, skipping all over and letting them cool completely.
Now, you want to grind the welds down to thin them out. You can't do any hammer and dolly on those welds. Be careful and use a nice sharp disc or you will create more heat and possibly more problems.
Shrinking those spots can be tough being you can't get behind with a dolly very easy while you hammer on the outside. Good old heating and cooling with air or water may be the way to go. Do this right at the weld that caused the high spot. A small dime sized spot heated up then cool is all you want. Now without a torch or a stud gun or something to heat, it's going to be tough. This may be a good time to look into a shrinking disc. That is a prefect spot for this tool, you run it over the metal and cool it, it's basically a "Heat block" and you only heat the high spots. http://www.ghiaspecialties.com/
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Yes, what I did was start at the front, then middle, then end, let them cool, then go place the next weld after the original first one. I thought I had read this method somewhere which is why I started doing it. Because--once again much like with my ORIGINAL filler sanding techniques in my other thread--I used to do my welds exactly as you described here, that is by splitting the difference. I never thought in a million years the way I had been doing it would cause what it did.
I figured the reason I got the warpage I did was because my metal didn't have enough of of a gap between the two panels at those spots (they were close).
Now, you're talking about shrinking the metal. I thought this entire time I should be stretching it because I shrunk it by welding it. If I'm understanding you correctly you're only talking about shrinking the peaks of the metal. Should this take care of the ripple as it extends farther down the quarter as well, or am I just SOL there?
I have a stud gun (which I use for shrinking), and I also have a 4.5" shrinking disc (which doesn't work well for me at all, but I think it's due to my angle grinder shaft having a slight wobble from an imbalanced wire wheel at one time). When I use the shrinking disc I'll notice that only one half of the disc is ever showing evidence from contact with the metal, probably due to the wobbly in my angle grinder, which means I'm not getting effective heat build up with the disc.