Oil canning - Shrinking disc, Torch or…?

[davinci2010]

Depends on how you were taught. I've never had good luck at preventing oil canning with the heat and quench method. That's what the hammer and dolly work afterward is for. The guy that taught me really did not put too much heat in the panel. I even saw him park a car in the Texas summer sun and use dry ice to pop the dents with no torches involved. He always worked the metal with a hammer and dolly after the dent was popped out to prevent the oil can effect. I followed his lead and it has worked pretty good so far. I do use a torch for a gentle fast heat prior to quenching. Also depends on the dent itself. You just have to read the situation and use the right method for it.

[uhohjim]

[QUOTE=davinci2010;243812]Depends on how you were taught. I've never had good luck at preventing oil canning with the heat and quench method. That's what the hammer and dolly work afterward is for. The guy that taught me really did not put too much heat in the panel. I even saw him park a car in the Texas summer sun and use dry ice to pop the dents with no torches involved. He always worked the metal with a hammer and dolly after the dent was popped out to prevent the oil can effect. I followed his lead and it has worked pretty good so far. I do use a torch for a gentle fast heat prior to quenching. Also depends on the dent itself. You just have to read the situation and use the right method for it.[/Q

Exactly right Davinci.I had an old guy originally from Europe who taught me alot of thing including the way I described my shrinking method.......guess it's all in what works for you.......and the end result.I've never tried the dry ice method but's something I may try in the future.....Jim

[davinci2010]

I probably don't have to say it but, don't touch the dry ice with bare skin! I never put a thermometer on the car after it was parked in the sun, but it was pretty hot. You could not touch it for long. This only seemed to work on hail dents that were pretty shallow and about the size of a quarter or less. Anything with a crease in the inverted crown of the dent required more hammer and dolly work instead of the heat and quench. This guy taught me a lot about working metal and I thank him for it.

[gusb]

Scientific test

#1 in attached pict is the original "oil can" area shown in the previous video. I put 7 MIG tacks down and everything went almost flat - but that adjustment pushed/created a new (smaller) oil can in area #2.

I then put 4 tacks in #2 area and the whole panel went more or less flat, with no more oil canning. This happened without any additional dolly/hammer work in the mix yet! The panel seems somewhat more stiff, but straight and flat. So I either just got lucky or this might be a decent way to shrink (when not having a good torch anyway) sheet metal. Seems a bit backward to create more grinding work but with all the welding on these quarter panels, a few more tacks to grind are no big deal for me. Also hit the area on the rear (not shown in photo) with a few tacks and it came flat too. So far I'm happy.

I just let the steel cool itself, no wet rag, etc. I don't get the wet rag/air quick cool thing everyone seems to do. I've always heard MIG welds are too hard for good hammer/dolly work - with gas/TIG welds being more "workable"? I don't know much about steel but it seems to me that quenching these areas when they're hot just makes everything harder, more brittle and less likely to move around with hammer/dolly? And these tacks seem to be doing a lot of shrinking even with a slow cool-down?

[davinci2010]

It looks like it worked out pretty well for you. As for mig welds being hard to hammer work, it depends on the filler. They make a easy grind filler wire for auto body work that is not only eaiser to grind off, but seems a little eaiser to hammer work afterwards as well. I have made " hammer welds " with Er70s6 and have not had too many problems. It also depends a lot on your base metal. Auto body metallurgy has changed a lot in the last 50 yrs. There's some techniques I use on the old stuff that I would not even think of on the new high strength stuff. Auto body is an art in itself.