55 cab roof large patch panel

[wilberweb]

Hi, guys has any one done a large area patch panel, I am having a heck of a time with my 55 Chevy 3100 cab top. I haven't any experience with patch panels.This is my first attempt and it seems like every thing was going great had all my seems perfect, all lined up correctly just the right amount of gaps,smooth looking all sides looked great, then I started to weld the patch panel, that's when the problems started.
when I started to weld the panel I noticed I was getting a dip in in the middle of the seem along the edge where the two seems came together, and when I would look across the roof I also noticed looking to the front of the truck it seemed that there was a large dip this wasn't there before I started welding. I didn't think that heat from welding a panel could cause this much problems? here are some pictures of what I am up against very frustrating it looks like the seem at the largest section started to dip in where the seems came together, and that the metal started to distort. Been working on this problem for a while. not sure if its me being to picky or is this normal for this large of a panel. and maybe that's what body filler is for
Hope some one is able to help.

Thanks


-Larry






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[dicer]

I'm not an expert, but as you weld, you need to jump around and not overheat the area, making lots of little spot welds, slowly filling in between the previous ones you did.
Two things are going to happen, either you are going to have expanded metal or shrunk metal, expanded is going to leave humps or high areas and over shrunk will pull it down and leave hollows. There are some good body working forums on the net, search them out.

[wilberweb]

Hi, Dicer
Thanks for the reply... yeah I found that out real fast.
I tried to go slow and mix up the welds but I must have got carried away with welding them too close and not spacing them. I found some great web sites that go in to some great detail on patch panels. its like that metal sure has some extreme shrinking or expanding qualities.Last night I was working on my truck and I relieved some of the welds and that panel straitened right out, its all correct alignment so that's not the problem its just technique and lack of skill. I am going to slow down and work the metal more slowly.

-Larry

[Kabwe]

When you weld in any panel the two most important things is panel fitment (on butt welds I don't like any gap or over lay the metal slightly touching if there is a gap it should be no wider than your filler wire) and keeping that metal cool. When you tack you panel in skip around and wait until you can touch the metal my hand before you continue welding. The longer you wait the better so what I do is tack work my welds down tack some more. That way by the time I grind (don't grind too much in one spot) my welds the metal is cool again. Continue this until the whole seam is welded up. Patience is a virtue when welding sheetmetal. The is no way to stop the metal from distorting you are trying to minimize it. It you have access to the rear of the panel it is always good to grind your welds and use you hammer and dolly to stretch the metal back as you go. When you do this only hammer on the HAZ (heat affected zone) the HAZ is where the metal charged color during welding. In you case you don't have access to the back so you will have to be patience and keep that metal cool as possible.

Also welding on a curve is easier than welding on a low crown or flat piece be extra have extra patience in those areas. I replaced my roof on my cab so I know your pain.

I hope this helps.

[dicer]

As far as shrinking there are a few ways to do it. I think one of the easyest is to heat the area and then a wet rag is put imediatly on the hot spot. If it needs to be expanded you can hammer on dolly cold and if you heat it red and lightly hammer on dolly it can shrink it, seems counter intuitive to me. Too me it looks like you are doing a great job.
Your biggest problem is that if the inner panel is in there you have no way to hammer and dolly it. To me sheet metal is a difficult thing to weld. Most always when welding heavy sections the problem is shrinkage, that is as the weld cools the metal is pulled tighter together. Sheet metal when bent into shape has that stress of bending into shape with in its structure, when its heated, that stress is relieved and the warpage occours. So the thing to do is keep the heat down, by jumping around, no long weld beads just spot tacks.

Just wondering why do you have to replace that section? Rust or damage?

[Kabwe]

When you weld the metal does not have to be shrunk it needs to be stretched. The heat from the welding has already shrunk that area. You better not apply heat to an area that has already been heat affected. To shrink a dent with that method is fine, but not a welded area. I don't use that method at all anymore I use a shrinking disc you have more control over the heat that is applied.

Hammer on dolly will stretch the metal back in to shape. See metal has memory and wants to go back to it's original shape. Thats why when you hammer a dent out correctly you will notice that when you hit one area and other area fixes itself. That's because you released the tension that was stop it from flexing back to its original shape. Its the same with the HAZ, hammer on the HAZ and you will see that warpage corrected itself in a place you never touched. Because the skrinkage in the HAZ is what caused the distortion.

Sorry If I was too long winded, once again I hope I shed some light on your issue.

[wilberweb]

Dicer,
I am replacing the piece that's damaged lots of rust. I had a cab top that came with the truck so I am replacing that piece, also as you can see the front of the truck is all rusted on one corner on the drivers side. I had the metal with all the seems tight not touching and I started to weld and that's when I got all the distorted problem so I cut the welds back apart thinking I did something wrong, so that's when I keep getting into problems now I have some gaps in my seems and just when I think I have it all lined up and start to weld on the metal its all misaligned I am afraid if I keep redoing it to try and get it perfect I will end up with more gaps and a piece that's no good.


Thanks for the advice Kabwe and Dicer
I had no Idea that welding in a panel was going to be this difficult. It didn't seems like the metal was not that hot, it was cool to the touch after a few minutes, with all the mistakes I have made welding and cutting the welds back apart to reset the panel it looks like a mess, I guess its like any thing that is difficult, the guys that have done it for awhile make it look easy. I will follow your suggestions hopefully I can make it work and not get into more of a mess. should I grind down the rest of the welds to make the panel look better or should I just work with it like it is and clean it up when I have it all welded in?

Thank
-Larry

[Kabwe]

Originally Posted by wilberweb

Dicer,
should I grind down the rest of the welds to make the panel look better or should I just work with it like it is and clean it up when I have it all welded in?

Thank
-Larry

You are asking the wrong person to answer this question.lol I'm a bit of a perfectionist so if its more than a 16th of filler that has to be used I would cut out and do it again, but if you don't care about how much bondo you use, you could continue and on with the patch. Its a judgment call on your part and I know I'm not sane when it comes to stuff like this.lol

[wilberweb]

Kabwe,
I know just how you feel I am the same way, its not bad its just 1/6" gap so its not extreme something I can live with, the panel isn't bad I think it should be perfect, its just me getting in the way, as you know when you take on a project like this you want every thing to be perfect if its not,when you get the truck all done it haunts you, when you look at the truck, and look back on the mistakes you made,maybe a part or panel I could have done a better job with.To every one else it may looks great. Its a curse I will work at it for a few days and let it sit for awhile and think about it. That always helps, stop and give it a rest.Then come back in a day or two and see it through fresh eyes.


-Larry

[dicer]

It was not a good idea to cut the welds to relieve it, better to do the hammer on dolly deal. And someone mentioned it only shrinks when welding I said that is true with thick materials. And can be true with the sheet metal. My brother did a roof fix one time, and he had the SHRINK it to get it to stop oil canning. And that is way before he ever put a hammer to it. Sheet metal is funny stuff. Heat will make it expand. I proved that with a heat gun on a electrical cabinet door one time, trying to remove a decal, I used too much heat and it stayed expanded, I tried to shrink it but was afraid of ruining the paint.

[Kabwe]

Wilberweb,

If you want to learn about metal go here http://metalshapers.org/101/jkelly/index.html. This is were I spend my time expanding my knowledge of working with metal.

I don't know how we got to oil canning, but oil canning can be caused by either
1. Over stretching
2. Over shrinking
All oil cans are different and must be approached individually.

[dicer]

Originally Posted by Kabwe

Wilberweb,

If you want to learn about metal go here http://metalshapers.org/101/jkelly/index.html. This is were I spend my time expanding my knowledge of working with metal.

I don't know how we got to oil canning, but oil canning can be caused by either
1. Over stretching
2. Over shrinking
All oil cans are different and must be approached individually.

We got to oil canning to explain what happened when heating the metal.
To try to explain how to resolve the problem!

[wilberweb]

Dicer,
I know you are right, I did realize that after I cut the welds I must have panicked...
I am going to pick up a few more body working tools at Harbor freight like a copper spoon,
some body hammers, butt clamps. that sort of thing.

-Larry

[wilberweb]

Kabwe,
I joined the Auto Restoration group, I haven't explored it yet just a brief look around looks like a great place to learn metal working, I haven't done a lot of body work but it seems the more I do the more I like doing it. It does get addicting, That's a great thing to be addicted too. beats other things. I think like a lot of things we do, its becomes a necessity.Body shops are expensive.

Thanks for the site Kabwe.

-Larry

[Kabwe]

Originally Posted by wilberweb

Kabwe,
I joined the Auto Restoration group, I haven't explored it yet just a brief look around looks like a great place to learn metal working, I haven't done a lot of body work but it seems the more I do the more I like doing it. It does get addicting, That's a great thing to be addicted too. beats other things. I think like a lot of things we do, its becomes a necessity.Body shops are expensive.

Thanks for the site Kabwe.

-Larry

Yeah man it is addicting. I've been doing this stuff for years and I continue to learn something with each project.

[wilberweb]

Dicer,
Sorry last post was to Dicer, I joined the auto restoration users group I addressed it to Kabwe. my mistake what is oil canning.

-Larry

[Kabwe]

Wilberwed,


Its cool because I understand some people like to be a butthead and I let people be who and what they are.lol So I'm not worried about Dicers little sarcastic remark.

I know the proof of what you know is reflected in the work you do and my work is posted on here for all to see. I don't talk about things unless I know what I'm talking about and I don't know anything about being a butthead to people so I will bow out of this conversation.

This is the link I meant to give you, I belong to too many forums.lol http://www.metalmeet.com/ the guys on here are incredible.

[wilberweb]

Cool,
I understand no worries.thanks for the link.
here is that front corner piece I mentioned in the previous post
I think this is going to be a interesting patch.

-Larry

[dicer]

I'm not trying to be a what ever. Just didn't understand the goofy attack. About the oil canning. I can't post pictures, I used to when you could post them on a site. Its all off site hosting, I don't do that.

And wow that is rusted out pretty good there. Need to get some kind of perservative up in that area of the cab.

[wilberweb]

Dicer

I guess I don't know all the lingo yet,
I didn't understand what oil canning is so it went over my head... may be Kabwe can tell us when he gets back on what Oil canning means, I have a off site picture posting web site. I found out how to post pictures direct just today I wasn't sure how to do it until I read kim57's post I don't know if that's OK to do?
On the corner rust portion I treated the rusted area with Ospho then encapsulated the rust with krylon rust tough rust hamm-R no need for primer its suppose to keep the rust from coming back I hope it works. I wont know until its all painted and the rust starts to come through that's the only way to know I guess.

-Larry

[dicer]

It wasn't you Larry, it was Kabwe.

Oil canning? It refers to the old timer type oil can that had a spout, and you tipped it upside down, put the spout where you wanted the oil, then pushed on the bottom of it with a finger and it flexed a bit and pushed the oil out of the can. Oil canning on the sheet metal is when its easy to push, kinda flimsy.
As far as rust, on mine I was going to use a small hose and a solvent type gun and blow in some zero rust paint.