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  #1  
Old 03-29-2010, 04:41 AM
jm11 jm11 is offline
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Default unrulely hood curve

Hi Guys, I am trying to make a one piece hood and as I add shape to the sides I find the side edges start to curve inwards If I remove some curve from the sides the edges straighten back out. I am a novice and I can't work out where Iam gonig wrong or what to do to correct this. Any all help appreciated,
Cheers
Jody
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  #2  
Old 03-29-2010, 04:51 AM
Einar_S Einar_S is offline
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I think you need to tell what you mean by "add shape" (shrink or stretch) and where you add it.

Other than that I suggest you make a small one first, like 50cm long. Then you can experiment with that with more ease and wasting less material while on your way to understanding what your sheet wants you to do.

I just noticed it's your first post here. Welcome!
And what's your name?
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Old 03-29-2010, 04:55 AM
David Gardiner David Gardiner is offline
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Hi Jody,

I take it you are wheeling this panel, if the 'hood' is supposed to be straight sided it should be a simple single curve and does not need wheeling. Simply bend it around something or use a set of rolls.

If I am wrong about the intended shape please ignore the above and give a little more explanation or photos would be good.

David
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Old 03-29-2010, 05:20 AM
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123pugsy 123pugsy is offline
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Pics would be good.

From the sketch it appears to be hour glass shaped towards the front.
That would be a reverse curve at that point.
I know how to bang out a reverse, but not too sure how to wheel one out though.

I would think the panel would need to be flipped and wheeled at those two areas.
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Old 03-30-2010, 10:02 PM
jm11 jm11 is offline
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Hi Guys thanks for the reply's, heres some more detail.
I'd really like to perservere with one piece.
I am using 1.6mm 5005.
All wheeling is from front to back.
After cutting the sheet to size I lightly wheeled the flat sheet giving it a very very light curve, which gave the flat sheet just a little rigidity or substance. - I'm not sure if I would do this next time.
Then using an inner tube on my top roll I rolled the curves for the sides, I used this method as while it is a simple curve it is a little different from front to back.
My panel then had to much curve thru the middle, too barrel shaped, I wheeled it thru the centre and lightly down the sides, this relived some of the side curve and allowed the panel to flaten out more right in the middle.
I wheeled more curve in and out till it sat on the cowl and nose fairly well and then tipped and flanged at the cowl end, then, tidied it up again and then tipped the nose end, and again tidied it up again.
The piece I have is not perfect and I suppose there will be may be other issues apart from this one, but overall its fits really well in form, gaps and hieghts, whats not working for me is how the side edges curl in.
When I ease up on the side curve by wheeling it with a little less curve or shape the edges of the sides will straighten or even curve outwards depending on how much curve I remove from the sides.
I have tried wheeling just the edges that are curved inwards but this makes it worse.
I have bashed the sides out on a bag but they curve right back in again as soon as I begin to smooth it out.
I am sorry I have no pictures my camera has just died.
I do think a smaller version is a great idea as its something I could physically handle on my own while trying to figure outs whats going on.
Cheers Again
Jody
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Old 03-31-2010, 06:56 AM
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Marty Comstock Marty Comstock is offline
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sounds to me like you are inadverntly creating a reverse. You probably didnt want to do any work on the sides, leaving them straight and flat with no shape. ANY work other than shrinking will cause what you see happening. This is a tough fix because it is over a large area, and flat is a bitzh. I would try a shrinking disc, or even possibly putting a rib down the inside of the hood to help ot keep its shape. Putting a 90 degree flande on the bottom too may help.

Anytime you are bashing or wheeling on it, you are stretching it. That would cause it to wibble wobble and look like a barrel or hourglass.

Marty
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Old 03-31-2010, 07:27 AM
David Gardiner David Gardiner is offline
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I would start again, if I am right the bonnet (hood ) should be a single curve ie. flat in one plane and curved to follow the body and radiator shell.
A bonnet of this type would be found on a '32 or model A or any car of that era. All bonnets of this type are single curve. If this is the type of thing you are making I think it would be a better idea to start again.
The material can be used on something with more curve later.

David
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Old 03-31-2010, 08:36 AM
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Kerry Pinkerton Kerry Pinkerton is offline
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Agree with other comments. What you have apparently done is stretched the sides...creating more surface area...and it HAS to go somewhere...so it goes in or out.

You might be using too much pressure when you have the inner tube on. Too much pressure will stretch the metal instead of bending. Also if you rollers are not concentric, you will get inconsistent stretching and on a panel without much shape, this will give you fits.

It's actually kind of difficult to do if you were trying to make it. My roadster has an intentional hourglass hood. Jay Pagnelli, Robert Kolenda, and I worked on it back at MM08 and it was kicking out butts because we wanted to top flat but have that hourglass shape:

1009Front2.jpg

Finally Jay talked us into cutting it into 3 pieces, shaping them separately, then welding them together. He is a welding monster.
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Old 03-31-2010, 05:00 PM
TheRodDoc TheRodDoc is offline
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your problem is what David said. Do not wheel the flat sheet at all. (NO Stretching)

If you put any compound curve in a sheet then try to bend a side down 90 degrees the edge will be loose. Causing it to either flop in or out in the center or even wavy.

Aslo trying to use a rubber wheel to bent a 90 degree radius bend is tough at best. You have to track very carefully. It you track a wider track in the center of the bend then the ends you get a barrel shaped bend. or the other way around a loose edge.

Or if you rubber isn't exactly the same thickness or hardness all the way around the sheet will be bent more in some places then another as it rolls along.

you would be better off to just cut the flat sheet then bend the sides over a pipe that is a little smaller then the smallest radius at the front of the hood. bend a little carefully not to kink the sheet. then slide the large radius end of the hood on the pipe a little and bend some more leaving the front of hood at same place on pipe. Make sure you mark the start and stop of both the front radius and the rear radius before you start.

here is a real quick drawing of a sheet that has been rolled in the wheel giving it a compound curve. Notice how the sheet is going to sit only on the ends of the pipe. when you bend that edge down it will come down in the center to the pipe but the outer edge of the sheet will be loose when the bend is finished. you would have to shring that whole edge to make it straight. Or stretch the radius full length to match the compound curve that was put into the top of the hood which will tighten the loose edge.

To put a curve in the top of a hood by hand is easy. (large flater type bends) just hold the sheet by the outer two edges. push the edges together bowing the sheet. As you push together twist the sheet back and forth.

(with the bow down one hand moves out away from you and at the same time one moves toward you. Then the other way and etc. pushing the edges together a little as you go.)

This stops the sheet from kinking as it bends. If it is too big to do by yourself then push the one edge of the sheet up against the wall where it meets the floor. That will hold the one edge for you while you push and twist the other. Or a leaf brake if you have one to hold one edge.

hood.jpg
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Last edited by TheRodDoc; 03-31-2010 at 05:03 PM.
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  #10  
Old 04-01-2010, 01:20 AM
David Gardiner David Gardiner is offline
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Couldn't have put it better myself! Good explanation Richard.
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