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  1. #1
    Join Date
    Feb 2009
    Location
    Bay Area
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    29

    Default Oil canning - Shrinking disc, Torch orů?

    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 at 02:53 PM.

  2. #2
    Join Date
    Sep 2009
    Posts
    9

    Default

    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.

  3. #3
    Join Date
    Dec 2008
    Location
    Arizona
    Posts
    812

    Default

    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.
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  4. #4
    Join Date
    Jul 2007
    Posts
    241

    Default

    Quote Originally Posted by gusb View Post
    Iĺve got two small spots on a quarter panel (extensive mig welding on the panel) that seem to need shrinking. Iĺve been teaching myself body work (idiot for an instructor ) as I go along and Iĺve 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? Donĺt mig welds in general usually ôshrinkö 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 ľ 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

  5. #5
    Join Date
    Jul 2007
    Posts
    241

    Default

    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

  6. #6
    Join Date
    Dec 2007
    Location
    Crete Illinois
    Posts
    186

    Default

    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. #7
    Join Date
    Feb 2010
    Location
    Houston, Tx.
    Posts
    378

    Default

    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.
    Sometimes there's no second chances.

  8. #8
    Join Date
    Feb 2009
    Location
    Bay Area
    Posts
    29

    Default

    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

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