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Oil canning - Shrinking disc, Torch or…?

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  • Oil canning - Shrinking disc, Torch or…?

    I’ve got two small spots on a quarter panel (extensive mig welding on the panel) that seem to need shrinking. I’ve been teaching myself body work (idiot for an instructor ) as I go along and I’ve read about using O/A torch or shrinking disc but I have neither.

    Does anyone know if putting a heavy mig bead/tack (say 1/8-1/4 inch) in the center of the oil-canning areas, and grinding that down would have any discernable shrinking effect on the surrounding steel? Don’t mig welds in general usually “shrink” sheet metal areas (instead of expanding)?

    Seems like the liquid weld puddle in the center might pull some of the stress out of the surrounding area. Just an off-the-wall idea – thanks for any feedback.
    Last edited by gusb; 07-30-2010, 02:53 PM.

  • #2
    I work in a car assembly plant as a dingman and have used a torch to shrink metal and I also own a disc but have never used it. We also have a shrinker which puts a localized heat into the area of contact. It works good but I rarley use it. I have never tried what your suggesting (seams similar to the shrinker) however I would think that it can be done effectively but I would just use a short tack burst with as high a heat as possible with out burning through. You may have to do a few of these and stratigically place them. You can more easily control the outcome.

    Another method you could try is cold shrinking using a 'slap file/spoon' or just a course body file with a dolly block. Hold the dolly block behind the area you want to shrink with light pressure, strick the surface with the slap file letting the dolly bounce back. If you hold the dolly with too much pressure you may end up stretching the metal instead.

    I would get a scrap peice of metal and practice your ideas and the method I suggested just to get a feel and see how things work out before you try it on the quarter panel. I hope this helps and good luck.

    Comment


    • #3
      You might try a cheaper alternative, haven't tried this myself. How about a propane plumber's torch? Lots cheaper than getting an Oxy/Fuel torch or a shrinking disc.

      Comment


      • #4
        Originally posted by gusb View Post
        I’ve got two small spots on a quarter panel (extensive mig welding on the panel) that seem to need shrinking. I’ve been teaching myself body work (idiot for an instructor ) as I go along and I’ve read about using O/A torch or shrinking disc but I have neither.

        Does anyone know if putting a heavy mig bead/tack (say 1/8-1/4 inch) in the center of the oil-canning areas, and grinding that down would have any discernable shrinking effect on the surrounding steel? Don’t mig welds in general usually “shrink” sheet metal areas (instead of expanding)?

        Seems like the liquid weld puddle in the center might pull some of the stress out of the surrounding area. Just an off-the-wall idea – thanks for any feedback.
        If you are teaching your self body work I would suggest you visit the site www.autobodystore.com .There are a lot of professionals on that site who will lead you in the right direction.BTW you dont need a lot of heat to shrink metal you typically heat a small dime size area at a time and rapidly cool it with a wet rag to tighten up floppy oil canned metal.If you can see steam coming out of the rag you are shrinking metal even a heat gun will work if thats all you have.I personally wouldnt use a mig bead to try and shrink metal you will just make a mess and thin your metal out when you grind the bead. Mike

        Comment


        • #5
          Forgot to add make sure you actually have an oil can which is metal that is loose and moves around when you press on it which is different than a warped panel due to welding overheating,in that case shrinking it may worsen the warping.Mike

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          • #6
            HI GUSB do you have access from the backside ?? Heat shrinking with a torch would be the way to go.Shrinking disc works well also but it helps if you have access so you can hammer and dolly before quenching with a cool rag.....Even with hammer dolly access heat and a cool water soaked rag will take alot of the warpage out......hammer and dolly make the process alot easier as you can flatten the panel after heating and quench with a cold rag to lock in(SHRINK) the area to keep it straight......takes soome practice but if you watch the metal you'll see it move and react to the heat and cool......Jim

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            • #7
              Sounds similar to the way I was taught to shrink small dents. Works best on dents about the size of a quarter. O/A is too hot. I use a propane or mapp plumber's torch. The metal does not have to be too hot; If water will sizzle on it, it's hot enough. Once the dent is heated, place a piece of dry ice on top and the dent usually pops out pretty nicely. Takes a little practice, If you have any scrap pieces use them first. Don't touch the dry ice with bare hands! I learned this technique from an old body man that used it to pop hail dents. This kind of repair can " oil can " if not finished out properly. It is just a bit lengthy to describe every detail in one post. There are a lot of good body work books out there that cover these repairs in greater detail.

              Comment


              • #8
                Thanks for all the feedback.

                See the video link below - I think this is "oil-canning" in one sample area?

                I can reach both sides...

                One thing that I've read in a few places (Frank Sargent's Metal Bumping, etc.) - one needs the O/A torch to get enough heat confined to a small enough area - to perform the hammer/dolly shrink correctly. I guess the idea being that propane, etc. gets too large an area hot - without getting the "dime-size" hammer strike area hot enough.

                I've done a few simple tests with a propane. In one case I heated the area a few times and cooled with the wet rag. I also tried heating the area and allowing to cool room temperature. These attempts the heat did create expansion and deform the panel but in each case the cooling brought everything right back to where it was with no change in the oil canning.

                What has changed the oil-canning is a bit of hammer/dolly work in outer areas. The lower horizontal line that shows below the area (see video) got a little work and that seemed to improve the area above - maybe some larger scale warpage creating the area in question, etc.

                So I'll try to go easy and may end up with a small torch set-up. Just don't really like the idea of O/A tanks in the garage.

                I guess the general consensus is the "shrinking" hammers with the pattern just mess up the panel and don't work?

                http://www.youtube.com/watch?v=87WH6t96YjQ

                Comment


                • #9
                  The video shows a pretty good example of " oil canning ". Generally I will pop the dent using the heat and quench method. Then I will work the outer ring of the dent with a hammer directed on a dolly behind. I prefer a smooth faced body hammer, but use a slight sliding motion with a lot of small taps as opposed to big hits. This has worked for me to keep the dent from oil canning after popping it. The serrated face hammers have their applications, but I don't like them for this. There is probably better and more modern ways to do this right, but I learned from old timers a few decades ago.

                  Comment


                  • #10
                    I guess the general consensus is the "shrinking" hammers with the pattern just mess up the panel and don't work?


                    The shrinking hammers work good if you are trying to cold shrink a panelI have a couple I use quite often and you can move alot of metal around with them with a little practice....The reason for O/A torch is exactly like you said brings the metal to temp fast rather than waiting for a cooler flame to do it...Heat small area work the metal and quench......Jim

                    Comment


                    • #11
                      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.

                      Comment


                      • #12
                        [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

                        Comment


                        • #13
                          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.

                          Comment


                          • #14
                            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?
                            Attached Files
                            Last edited by gusb; 08-21-2010, 05:58 PM.

                            Comment


                            • #15
                              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.

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