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Old 01-09-2009, 12:12 PM   #1
kidsandJeep
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Default Shrinking Distorted Sheet Metal

Hello,

Could someone please help me understand how to shrink out oil canning/distortion in a body panel? I am practicing and now know (well I knew heat was bad before just not how much) that heat is the real enemy when installing a patch panel, my question is how to I fix oil canning? I have experimented with just welding in smaller patches in the oil canning areas and this works. I have also tried shrinking with a torch and water but this didn't work so well. My current patch technique invloves butt welding in a piece of 18g with short tack welds (Lincoln 180C w/ factory settings) and hitting the tacks with compressed air as I work. My earlier patches had the oil canning/distortion from too much neat and I am fixing these now. Any tips/advice would be appreciated.

Thanks,

--Scott
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Old 01-09-2009, 12:25 PM   #2
Randy Ferguson
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Default Re: Shrinking Distorted Sheet Metal

Hi Scott,

Read my blog. If you have more questions after reading it, I will more than happy to answer them.

http://fergusoncoachbuilding.blogspot.com/

Randy Ferguson
www.fergusoncoachbuilding.com
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Old 01-09-2009, 12:37 PM   #3
kidsandJeep
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Default Re: Shrinking Distorted Sheet Metal

Thanks Randy, Great tutorial, wish I had seen that months ago. I'll give your techniques a try. I have only been using a tack-tack method not running 1 inch beads because of fear of over heating. I like the cutting disk idea also, I have been useing a 36 grit flap disk, just hitting the proud bead, again keeping the heat down. Are you using an Eastwood Shrinking Disk? I have seen it in the catalog maybe I need to invest, the idea is it pull the metal like a slapper to shink out the distortion, right?

--Scott
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Old 01-09-2009, 12:38 PM   #4
kidsandJeep
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Default Re: Shrinking Distorted Sheet Metal

Beautiful work by the way!
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Old 01-09-2009, 01:01 PM   #5
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Default Re: Shrinking Distorted Sheet Metal

Randy,

Great tutorial. And VERY nice work.
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Old 01-09-2009, 02:41 PM   #6
nismomans13
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Default Re: Shrinking Distorted Sheet Metal

that is VERY nice work. Most of my welding is on heavy material, i still struggle with the thin sheet metal.
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Old 01-09-2009, 11:19 PM   #7
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Default Re: Shrinking Distorted Sheet Metal

Kidsand jeep - First thing you need to know - the metal after welding needs to be stretched, not shrinked (shrunk?) due to the weld heat pulling the two metal pieces together.
I agree Randy does some nice work, but he's working on a relatively THICK gauge of metal, that used on earlier vehicles, which I would argue are MUCH easier to weld on with that much overlap (read: HEAT). If you try that with a mid 70's and up vehicle, I'd imagine many people burning through the original piece being repaired!
For thinner metal used in 70's and up vehicles, I prefer to use the same method, but not to overlap the welds. There's really no need to. Just make sure you move the weld zone around, so as not to add more heat than necessary, until the panel is fully welded.
In the case of thinner sheet metal used in "newer" cars, most would prefer to have a slight gap between panels being welded, as it reduces the distortion that you have to work after welding. Eastwood makes some good butt-weld clamps(below), but I normally just use a thin screwdriver to set the gap, then clamp the two pieces togther with a strip of copper in behind. The copper sucks up a lot of the heat, thereby reducing the HAZ even more. It also keeps the weld beautifully flat on the other side which saves a lot of finishing time on the underside of a panel - if it will show!





As for using a shrinking disc, this is fairly advanced stuff, few are available (Sunchaser or self-made) and I have found - after many years of this - they aren't that effective in a welded zone, due to the hardened nature of the weld itself (mig specifically). You're advice to hammer on dolly is what's needed here, especially for a beginner/intermediate metalman!

As for "shrinking" with a torch and wet rag (quenching), this is used when the metal has been stretched due to collision, or if you ended up strecthing some spots when hammering on dolly a little too far. A great way to "watch" the high and low spots is to shoot a light coat of flat black paint (or any color) over the repair and then lightly go over it with a sanding board. You'll immediatly see the spots you need to pick up, knock down or move around.
Good luck and post some pics!!
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Old 01-10-2009, 12:12 AM   #8
Randy Ferguson
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Default Re: Shrinking Distorted Sheet Metal

The shrinking disc I use is from Wray Schelin. He's a master sheet metal shaper and makes very high quality tools. I think there's a link to his ebay auction on my website. If not, just search shrinking disc on ebay and it should pop up. He also sells an instructional video for using the disc. It's very simple with just a little practice.

e-tek, I've worked on countless "newer" vehicles and use the same technique as with the 19ga (.042) I prefer to have a very tightly butted seam as opposed to the gap method. It's personal preference and if you're successful, roll with it!!

Scott, as for your oilcanning/distortion. Work within the Heat Affected Zone to get it smooth and you should be in good shape. If the panel was good before you welded in the patch panel, then the only thing causing the distortion is from the shrink occurring during the welding process.
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Old 01-10-2009, 09:26 AM   #9
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Default Re: Shrinking Distorted Sheet Metal

I need to weld a panel on my car that I can not get to the back side..What is the best way to deal with that ?? It is in the cowl .and will about 20" X 6" Thanks Jamie
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Old 01-10-2009, 01:17 PM   #10
Randy Ferguson
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Default Re: Shrinking Distorted Sheet Metal

Vern,

Can you post a picture of the area?
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Old 01-10-2009, 03:17 PM   #11
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Default Re: Shrinking Distorted Sheet Metal

sure I will go take a pic..
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Old 01-10-2009, 03:41 PM   #12
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Default Re: Shrinking Distorted Sheet Metal

Ok here is two pics.. Thanks

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Old 01-10-2009, 07:38 PM   #13
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Default Re: Shrinking Distorted Sheet Metal

If I may, htere's a few ways you can go here. Obviously mine are just my preferences and others will have different, maybe even better methods!
One way would be to weld some tabs onto your patch panel, so that when you set it into the hole, the tabs would hold it in place. You'd then spot-tack different areas, working around the perimeter to minimize distortion. Without access to the backside, you'll only be able to work down high spots, then will have to fill any lows after grinding. Remove the tabs once your weld are holding it solid.
If you want to metal finish, or use minimal filler, you would need to cut an access hole somewhere - under the dash or in the cowl. I'd cut something just big enough to get a handled dolly in behind, which would alow you to work it quite proficiently.
Looks like a cool project!
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Old 01-10-2009, 10:08 PM   #14
Randy Ferguson
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Default Re: Shrinking Distorted Sheet Metal

I would have to agree. Working in areas with no access is always a challenge.

Good luck with it. Keep us posted.
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Old 01-10-2009, 10:14 PM   #15
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Default Re: Shrinking Distorted Sheet Metal

OK I will have to think about this LOL.. Thanks very much for the help.
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Old 01-11-2009, 09:59 PM   #16
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Default Re: Shrinking Distorted Sheet Metal

Ok here what I am thinking.. I am going to frange the sides,make a lip with my bead roller. there are two small holes I can stick something though and hold it up in place. leave a gap and try to keep the weld in the gap.tack-weld and try to cool it each tack weld with ????? air or damp rag and lay a piece copper on it ? grind the welds and cool as I do that too ?
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Old 01-11-2009, 10:41 PM   #17
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Default Re: Shrinking Distorted Sheet Metal

So you're not butt welding it?

Rapid cooling has little to no effect on warpage. I've been down that road and saw no real advantage to it. The metal in the Heat Affected Zone (the blued area after welding) is going to shrink regardless. It's this shrinkage that causes the warpage even beyond the heat affected zone. By stretching slightly within the heat affected zone will relieve those stresses and the distortion will disappear.

Last edited by Randy Ferguson; 01-11-2009 at 10:59 PM.
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Old 01-12-2009, 11:34 AM   #18
kidsandJeep
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Default Re: Shrinking Distorted Sheet Metal

E-Tek/Randy,

Thanks for your thoughts and help with this. I know that heat is the enemy when welding in these patches. I have been using the Eastwood butt weld clamps and try to move the HAZ around, from what you're both saying I am missing the step of stretching the metal in the HAZ after welding. I am going to read back on this but do either of you cool (air/mist), sounds like neither of you do, the HAZ after you stretch (hammer/dolly) the area? I am guessing rapid cooling would negate the stretching that was just done, meaning it would shrink the metal in the HAZ.

I would post pics, but I have one panel that looks like Dr. Frankenstein was trying to create something, maybe when my work looks a little better. The idea for my project was to add a small stretch in the jeep to create a little more room, then dealing with the rust etc. I think I have too many peices in there. I think I need to remove the whole thing and start with a new larger panel. I ordered a shrinking disk to try on some practice panels, I didn't care for the torch/quench method to shrink. I am sure I was doing something wrong..... With oil canning (stretched areas) the shrinking disk should do that type of work, right? Shrinking the area around the oil can should tighten the panel????

You help is greatly appreciated.

--Scott
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Old 01-12-2009, 01:52 PM   #19
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Default Re: Shrinking Distorted Sheet Metal

You'll want to make your "shrinks" right on, or near, the tops of the high spots, this is where the shrink will reverse the stretched metal. I think you know this, but the spot you heat to red is only step one. Step two is on-dolly hammering of the metal in circles towards the centre where you heated it. If you need more explanation, let me know.

Don't think you ever posted pics of the larger area/project you just referred to did you? GO ahead and post it - I've done lots of crappy looking work in the past - that's how you learn! A good quote from a builder I heard was: "It's only "effed" if you can no longer work it."

As for cooling WHILE you're welding - NO. The heat from the weld has already done it's thing....cooling it quickly won't do anything more. Sometimes buildedrs use air - but mostly just to not melt/burn any attached parts!
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Old 01-12-2009, 02:52 PM   #20
kidsandJeep
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Default Re: Shrinking Distorted Sheet Metal

e-tek,

I read the book "Metal Bumping" and the torch/shrinking procedure is pretty well explain in there, not that I can execute it correctly. Like anything practice probably makes perfect. I'll work on posting some pics of my project, feedback would be appreciated.

--Scott
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