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Help with cab door oil canning
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orwell84
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PostPosted: Sun Jul 22, 2018 2:29 pm    Post subject: Help with cab door oil canning Reply with quote

I have been fighting with oil canning in a baywindow bus cab door for longer than I would like to admit. The bus had large van mirror on it and had holes drilled in the door at 3 point for the supports. The metal around the holes had been stretched inward. I welded up these holes which turned out to be a very bad idea.

I ended up with an oil can that I have chased all over the door, which may have been there to begin with, but was likely made worse by welding the holes and shrinking when I should have stretched. At this point, I have brought the door pretty close to contour, but still have oil canning in the middle of the door. I have tried stretching the area slightly higher and going over it with a shrinking disc but I always seem to end up with an oil can in or near the damaged area no matter what I do. I did end up getting rid of the shrinking from my welds and the door is close enough to not require much filler. I would fill it if I didn't have the oil can.

At this point, I am considering either getting a new door skin or used door as I don't think I can get this out. I would farm this one out, but am not sure whether regular body shops do much metal shaping anymore. The photo is probably not very helpful. The red circle is where the oil canning is.

Thanks for the help.



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theKbStockpiler
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PostPosted: Sun Jul 22, 2018 7:05 pm    Post subject: Re: Help with cab door oil canning Reply with quote

I would heat up an area but not red hot, and hammer off dolly a few inches from the dolly. Get it just hot enough where you know the metal is just barely giving in when you hammer it. Place the dolly on the non stretched part.
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PostPosted: Sun Jul 22, 2018 7:11 pm    Post subject: Re: Help with cab door oil canning Reply with quote

I'm sure the body/paint Gods will strike me down for offering this, but I had an area on my rear quarter panel with that same problem. Like you I tried to no avail to get rid of it by shrinking and moving the metal. I eventually gave up, because I had the whole rest of the car to finish, and took a strip of metal and bonded it to the backside of the oil can area. This essentially braced it and made that area more rigid. I used some panel adhesive and wood bracing on it until it dried. No more oil can. Moving on.
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PostPosted: Sun Jul 22, 2018 7:47 pm    Post subject: Re: Help with cab door oil canning Reply with quote

I've found the easiest way to fix oil canning is to just replace the part or re-skin. I worked on a hood once and tried everything in the world to remove the oil canning and just gave up and bought a new hood.
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orwell84
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PostPosted: Sun Jul 22, 2018 8:33 pm    Post subject: Re: Help with cab door oil canning Reply with quote

theKbStockpiler wrote:
I would heat up an area but not red hot, and hammer off dolly a few inches from the dolly. Get it just hot enough where you know the metal is just barely giving in when you hammer it. Place the dolly on the non stretched part.


Just so I understand you correctly...

You are suggesting shrinking along the edge of the damaged area close to the undamaged area so that the shrinking and tightening happen close to good metal that is better supported and will have less chance of caving in. The off dolly hitting would level the shrunk area with the surrounding good metal. I could skim this area with the shrinking disc or even a paint stripping wheels to get it warm and hammer it with a spoon.

I think the bracing idea is pretty good. I can be a bit of a purest when it comes to metal but sometimes you have to get on with your life. Those low crowns are a bitch when they go out and and those old school metal shapers did not pick those skills up overnight. I'm good with minimal filler on top of good metal and I don't like to bodge body lines, but otherwise....

A new door skin might be an option, I just don't know how good the repros are and if they are the same thickness of metal. I would also consider a good used door.

Thanks so much for the great suggestions.
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theKbStockpiler
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PostPosted: Mon Jul 23, 2018 2:06 pm    Post subject: Re: Help with cab door oil canning Reply with quote

That is what I meant. Very Happy

If you don't start on the outside and work your way in ,it tends to create more damage (gather up all the access metal) and you have to work it out last all in one spot with all the metal fatigue in a small area.

Most of the bulge is caused by stretched as opposed to bent metal and the metal has to be hot to some degree to shrink it without crumpling it. Red hot is best for shrinking difficult areas like a crease and hitting it directly. I find the best results from heating a area up red hot or below it and having the hammer overlap the hot area very slightly until it is almost completely worked out. Then lastly you hammer down the last very small (dimple) part.

I have only used a torch/hammer and the water method to shrink and both of them make a spot rise and then you have to hammer that smaller high spot down. I think the water method will cause a bigger shrinked area but you still have the raised part to hammer down.

From the videos I have watched the disc method does not look effective. Do you still have to hammer part of it down?
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orwell84
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PostPosted: Mon Jul 23, 2018 5:32 pm    Post subject: Re: Help with cab door oil canning Reply with quote

theKbStockpiler wrote:
That is what I meant. Very Happy

If you don't start on the outside and work your way in ,it tends to create more damage (gather up all the access metal) and you have to work it out last all in one spot with all the metal fatigue in a small area.

Most of the bulge is caused by stretched as opposed to bent metal and the metal has to be hot to some degree to shrink it without crumpling it. Red hot is best for shrinking difficult areas like a crease and hitting it directly. I find the best results from heating a area up red hot or below it and having the hammer overlap the hot area very slightly until it is almost completely worked out. Then lastly you hammer down the last very small (dimple) part.

I have only used a torch/hammer and the water method to shrink and both of them make a spot rise and then you have to hammer that smaller high spot down. I think the water method will cause a bigger shrinked area but you still have the raised part to hammer down.

From the videos I have watched the disc method does not look effective. Do you still have to hammer part of it down?


I think I have been getting a high spot in the middle of a shallow low spot, get frustrated and shrink that spot and start all over again. I stretched the leading edge of the repair even some of the untouched metal just lightly with a slapping spoon and dolly, before trying the technique you described. Just stretching a little there seemed to relieve the oil can a little. There is also a square patch that tends to stay low that I am working up It is a bear to stretch but seems to be a point of tension where the oil can breaks. The high spot and oil can seem to be moving toward the top of the door. I am going to try to work it in that direction using that kind of heat a little, shrink a little, slap a little off dolly in that direction and hopefully lose it in a more forgiving section of the door...if that makes any sense. It seems to even out the tension in the panel, support the shrink and give it somewhere to go. As I bring the spot up to a more uniform contour the metal seems to hang together more. It's not a severe oil can at this point, just flexing in one spot when pushed.

If that doesn't do it, I will do the panel adhesive and brace thing. I can live with that. It's otherwise a decent original door. I can also live with the filler in the other door with the exact same damage, minus me beating the shit out of it for 2 weeks. Bondo brand filler from the hardware store. Been there since 1991. I will let you know how it goes. Thanks again for the help.
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theKbStockpiler
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PostPosted: Mon Jul 23, 2018 6:48 pm    Post subject: Re: Help with cab door oil canning Reply with quote

Something else that I have learned is that if you keep some pressure on the hammer after you hit a spot it pushes it in more. If you just smack it the metal rebounds back out some.

I think if you move the high spot to the edge it is going to make the panel longer.

If you decide to brace it you could spot weld a strip of 20 gauge in there.
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orwell84
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PostPosted: Tue Jul 24, 2018 5:21 am    Post subject: Re: Help with cab door oil canning Reply with quote

theKbStockpiler wrote:
Something else that I have learned is that if you keep some pressure on the hammer after you hit a spot it pushes it in more. If you just smack it the metal rebounds back out some.

I think if you move the high spot to the edge it is going to make the panel longer.

If you decide to brace it you could spot weld a strip of 20 gauge in there.


I'm not sure how moving the high spot to the edge would make the panel longer. Just curious. I guess what I mean is shrinking the high spot in the direction of the top of the door, more like supporting above the damaged area with the dolly when I shrink the high spot down. I have used the disc for shrinking lately because it lets me heat spots of metal just a little. I also have a shrinking attachment for a mig welder which tends to make small hard shrinks and a carbon arc torch which is hard to see and control for shrinking.
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PostPosted: Tue Jul 24, 2018 9:27 am    Post subject: Re: Help with cab door oil canning Reply with quote

Quote:
I'm not sure how moving the high spot to the edge would make the panel longer. Just curious. I


If the bulge is in the center of a panel , the area around the bulge forces the extra metal up.If you shrink the bulge at the edge the extra material is going to go out.

I use MAP gas and with 20 gauge you can get a radius of about 1 1/2" red hot. I don't see videos with people using oxy/acetylene doing much more.

You don't have to get the area red hot to shrink
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PostPosted: Tue Jul 24, 2018 11:45 am    Post subject: Re: Help with cab door oil canning Reply with quote

Ok, I get what your saying. Moving the bulge into an untouched area would displace that metal and a bulge or oil can might pop up somewhere else. Best to shrink it within the area of highs and lows where it lives and try to even it out with a low spot.
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PostPosted: Tue Jul 24, 2018 3:25 pm    Post subject: Re: Help with cab door oil canning Reply with quote

I'm tied up in another project so I can't test this myself immediately. Why not heat up a test piece but not enough so it bulges out and try to press it down with a dolly behind it?
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PostPosted: Wed Jul 25, 2018 5:13 am    Post subject: Re: Help with cab door oil canning Reply with quote

I think I have figured out why I can't get this panel right. I had welded in a square patch to repair one of the holes at the front of the door. I have since learned about why using a square patch is a bad idea unless you are patching a shipping container. This patch seems to be the point where the panel starts to yield when pushed. I have tried stretching it, pulling it out with a stud gun bumping behind it and even stretching the welds with a pic hammer on dolly. It seems to want to go a different way from the rest of the panel. I could cut it out and weld in a new one with radiused corners, but I don't know if that would make things any better. I was very careful welding it in and have long ago stretched out the very predictable shrinking this patch makes. I have really learned the lesson of why not to weld in the dead center of low crowned panels
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PostPosted: Wed Jul 25, 2018 7:56 am    Post subject: Re: Help with cab door oil canning Reply with quote

I don't think the shape of the panel has any merit. When I read the explanations there is no direct reasoning.It sound like any other B.S . I have heard.

I think your issue is that you only have to shrink the area a slight bit which is finesse work and why it's difficult to do.

Heating up the entire area may not be the right way to do it. How are you using the shrink disc?
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PostPosted: Wed Jul 25, 2018 9:04 am    Post subject: Re: Help with cab door oil canning Reply with quote

I have been using it either to shrink specific high spots and tap them down or gone over the whole area lightly to highlight highs and lows which doesn’t put much heat into it.

I get your point about the shape of the panel not really mattering. Whatever shape it is, it needs to be brought back to its original contour to retain its strength and rigidity. Low crown panels in places with less support are just more likely to oil can when they are out of shape. My point about the patch is that it is square and flatter than the rest of the panel and creates a low spot that is hard to work out and prevents the rest of the panel from going back into shape. This is a stretching problem rather than a shrinking problem. The patched section has to be stretched more to allow the panel to go back into shape. It will just be harder to stretch. I think this why shrinking isn't getting me anywhere. At least, that's my best guess as to what is happening at this point.
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PostPosted: Thu Jul 26, 2018 8:02 am    Post subject: Re: Help with cab door oil canning Reply with quote

I would just go by matching the contour and not worry about the oil canning first. If the contour is absolutely perfect and still oil cans, THEN I would shrink or stretch it very slightly.

I recently did a project involving a mower cart/trailer. Laughing I was in a hurry welding and I warped the panel I replaced all to hell. I spent about 2 1/2 hours on it but I got it flattened out so it would need almost no body filler. I used 3 disposable tanks of MAP gas to do it but I wanted to learn how to do it so I would have the skills for my beetle.

If you did not convex the patch piece then it has to be too flat. A piece with shape will have more resistance to oil canning. I may do a test piece later today.
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PostPosted: Thu Jul 26, 2018 6:49 pm    Post subject: Re: Help with cab door oil canning Reply with quote

I put a bulge in a test piece .With the water/torch mothod I got some of it to shrink but then I could get no more progress after a point. I went from about 400 degrees to glowing red and both worked to a point but the force of the contracting metal would not pull it all out.
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PostPosted: Thu Jul 26, 2018 7:12 pm    Post subject: Re: Help with cab door oil canning Reply with quote

It's for sure the patch. I stretched it out a lot hammering on dolly. It's now a small tight high spot but the rest of the panel holds it shape without any flexing, though it still has some low spots to work out. I will have to shrink the patch and probably some of the surrounding area to get it back into contour, then work out the rest of the panel. It's a little harder to work the metal where I patched it but I don't think welding in a new one would really make much of a difference. Thank you for doing your test.

It comes down to me having not understood what was going on with the panel and over or underworking things because of lack of experience.
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PostPosted: Mon Jul 30, 2018 5:30 am    Post subject: Re: Help with cab door oil canning Reply with quote

Still slogging away at this. I was not able to get the patch to stretch enough where I needed it to and it is in a hard place to get a dolly behind it. It was creating a low spot that I could not raise enough to get the shape of the panel close enough. I ended up making a new patch and forming it to the shape of the contour. I worked the surrounding area into the right shape before tacking it in. Hopefully I will have to fight with it less to work it into the correct shape.
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