[Robznob11]

Originally Posted by chevy72blu

I have never welded sheet metal (plenty of thicker stock) but I plan to start learning in the near future. Can someone explain what oil canning is? Its obviously from too much heat, but what happens? The metal crinkles or something?

Thanks

Well it a combination of heat expansion and then metal shrinkage! When you put a patch in there is a gap between the oe metal and the patch. As you stich it in no mater how slow the metal gets hot and a puddle fills a small portion of the gap. As it cools it shrinks and pulles the open gap together. On flat pannels expecially if your doing a 4 sided patch as the gaps try to pull together it sinks in like a dent. The oe metal aslo wants to go to its original shape so with a slight push from the inside it will pop out and back in easly. Kinda like having a wobbly knee with no support. If you try to leave it like that and fill it the filler will eventually seperate because the metal behind it has no support. Thats why if your going to do a patch like that you need very tight gaps alot of time and you need to hammer the welds along the way. Also you dont want any 90 corners. If you round them it lessens the hot spot where two sides meet. I have also had better luck doing one side at a time as opposed to working the full patch. This way you only get pulling in one direction at a time. Any way you look at it your going to have hammer and dolly time. And unless you are a way awsome metal worker your gonna have filler. Hentce that is why i now way the pros and cons of fixing or patching. Remember the oe dent can be shrunk back just as easy as working a patch. Now rust is a different story! I hope this helps someone
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