How to straighten sheet metal?

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How to straighten sheet metal?

Postby allenlook » Sat Mar 25, 2006 8:12 am

My latest acquisition has some bent and wrinkled sheet metal, especially the grille.

While I could leave it as-is, I'd sure like to straighten it out somehow. I was thinking of banging on it with a dead-blow mallet, but something tells me I'd only thin and stretch the metal out like a pie crust.

Also the grille has a lot of small sheet metal cross-ribs that need to be straightened out and I can't picture how to do that...

Any suggestions?
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Postby Don McCombs » Sat Mar 25, 2006 8:55 am

Allen,

You need to correspond with psycho.

http://www.farmallcub.com/phpBB2/viewtopic.php?t=12386
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Postby l5foye » Sat Mar 25, 2006 8:59 am

Can you post a photo of what needs work? To avoid stretching metal, normally you use a shrinking hammer - the head of which is serrated.
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Postby Patbretagne » Sat Mar 25, 2006 1:19 pm

l5foye wrote:Can you post a photo of what needs work? To avoid stretching metal, normally you use a shrinking hammer - the head of which is serrated.

Tell more, this is very interesting, something I have avoided doing as I always seem to have a bump when I've finished flattening some sheet metal, I have a feeling that I am not alone????
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Postby George Willer » Sat Mar 25, 2006 3:30 pm

Pat,

Right now I'm in the process of making a hood for Rambo from a junk hood. I've welded a lot of stray holes that have been drilled for no known reason, and have welded a bunch of cracks and replaced the missing front brackets. I've also replaced the metal someone has cut away in the worst possible side of the radiator neck. I have nearly all the paint removed and am looking towards the final straightening of the many dents. There are a number of areas that will require shrinking the metal. I intend to do it with the torch.

Heating any small area to red hot, and straightening any resulting bulge will result in shrinkage when it cools. The technique requires heating a very small pinpoint to red and moving on to another in the same general area. It may result in too much shrinkage, but we know how to deal with that... work it "on dolly" until it is straight.
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Postby Jim Becker » Sun Mar 26, 2006 12:55 am

George Willer wrote:It may result in too much shrinkage, but we know how to deal with that... work it "on dolly" until it is straight.

George just barely touched on a key concept. Working "on the dolly" is the use of a back up block directly behind the point you are hammering on. This technique stretches the metal. Working "off the dolly" is done by putting the back up behind a low spot while hammering on a high spot.

I don't know what I am doing straightening metal. But I can fake it well enough to fool the mildly observant. The little I know all came from reading a book "The Key to Metal Bumping" by Frank Sargent, third edition, 1953. Get a copy, read it and do what it says. You will be surprised how much you can do.

I got a copy from Eastwood a few years back. Eastwood still has it listed but Amazon lists it as out of print.
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Postby Patbretagne » Sun Mar 26, 2006 2:22 am

Thanks George and Jim, Will try and also will try to get the book
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Postby Bus Driver » Sun Mar 26, 2006 7:59 am

Do a lot of looking before using the hammer and dolly. The best process involves moving the metal in exactly the opposite sequence to the process of creating the dent or bend. The outer edges of the dent were formed last, so start at the point that you believe bent last- the perimeter. work inward to the point of first impact. Use gentle blows, harder blows can come later if necessary.
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Postby Jim Becker » Sun Mar 26, 2006 10:01 am

Bus Driver wrote:The best process involves moving the metal in exactly the opposite sequence to the process of creating the dent or bend.

This makes a big difference in how easy and how well the damage comes out. (It's in the book.) To add a bit to this, a lot of dents are the result of a glancing blow that forms a crease. Always start at the newer end of the crease. If you look at a craese caused by a blow from left to right, the metal will be pushed to the right. So start at the right end and work to the left.
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Postby Harold R » Sun Mar 26, 2006 10:07 am

That's good to know. Unfortunately, I don't think I'll have time to work some small dents out of the lo-boy I'm bringing to Texas. :oops:
Never enough time. Pitiful how a job gets in the way of a fun hobby! :lol: :lol:
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Postby Psycho » Sun Mar 26, 2006 11:48 am

Sorry,
I read this one a little late. These guys covered it pretty well. I'm no pro, by any stretch of the imagination, but what I've learned, I learned by doing it wrong the first time. I started out with one of the simple bodywork kits you can find almost anywhere(2 or three hammers, and an assortment of dollies). I've learned that less is always better with a hammer and dolly. You can always hit a little more later, but overdoing it is harder to correct. Have fun with it. If it's getting frustrating, put it down and go have a coffee or something. Come back later, it will still be there. The key is to have fun :lol: :lol: :lol: Would like to see pic's of what you're working on.
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Well...

Postby allenlook » Sun Mar 26, 2006 3:30 pm

Fantastic info guys, thank you!

I took some pictures today and will post shortly - from your description I have the "hood from hell" :evil: and there is no chance that it will be restorable with hand-hammering. I also have the "grille from hell" to back it up.

By the different bends in the muffler and air cleaner cap, and in the hood and grille itself, I think a tree or something landed across the hood of the tractor and the previous owner unleashed a pack of gnomes with hammers to beat out the dents.
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Bent sheet metal

Postby allenlook » Sun Mar 26, 2006 7:52 pm

OK, here's the pictures of the hood and the grille. Looks like I have several problems...

First - the previous owner cut the radiator hole very oversize...

Image

Second - the rest of the grille is in rough shape.

Image

Third - the exhaust hole is similarly crude.

Image

Fourth - I have this bump and hole in the hood.

Image

Fifth - most of the hood has what looks like "metal acne."

Image
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Postby Patbretagne » Mon Mar 27, 2006 3:50 pm

Allen, looks like you are going to get some metal-bashing practice in!
The last photo of an ackné'd Cub is extrodinary, it must still be in it's teens!, Good luck, keep us posted
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