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  #11  
Old 05-03-2021, 04:02 PM
crystallographic crystallographic is online now
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Another thing maybe worth mentioning is the size of the dies.

Since leverage over the panel is needed for making the ruffle and trapping it down.

Small 2inch dies are ideal for small panels that need shrinking 4-5 inches in.
3inch dies are good for 6 to 7inches in.
4inch dies can go 8 to 9inches.
5 and 6inch dies can go even farther.
I've seen 12inch deep shrink marks on large panels made in the 1930's. = big damn dies and slow chomping.
But this is of course, based on the previous concepts being addressed:

die geometry, clearances, and contact spots.
I knew of one Yoder guy who had a hammer with a bar welded in place to limit the downward force of the upper die - just for shrinking. It was an old hammer that was set that way many years before I was there, 30 years ago.



It was known back then that some of the big power hammers were set up and dedicated to one task - shrinking, or large low-crown panel working - as only two instances. But that was then .... new ideas now.
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  #12  
Old 05-04-2021, 09:25 AM
Bart Bart is offline
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Thanks guys, some really great information there.
Im always learning so much from all of you.
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  #13  
Old 05-05-2021, 08:22 AM
Bart Bart is offline
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So i got the front to back to curve nicely but the sides have flattened out. I got the sheet sitting on a buck but the sweeps show a better picture what on i mean.

181625694_894089497803976_6847652046472122984_n.jpg

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180673461_301689328273081_1454190560564864545_n.jpg

180656782_330834048462702_8198379027280304100_n.jpg

181580016_256617109541479_7145408313560389844_n.jpg

181543301_309766540676883_7709907215013926788_n.jpg
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Last edited by Steve Hamilton; 05-05-2021 at 01:18 PM.
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  #14  
Old 05-05-2021, 02:18 PM
crystallographic crystallographic is online now
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Quote:
Originally Posted by Bart View Post
So i got the front to back to curve nicely but the sides have flattened out. I got the sheet sitting on a buck but the sweeps show a better picture what on i mean.

Attachment 59888

Attachment 59889

Attachment 59890

Attachment 59891

Attachment 59892

Attachment 59893

Hi Bart,
I'm looking and looking at your pix and I am not seeing your trim lines marked out.
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  #15  
Old 05-05-2021, 03:51 PM
Jaroslav Jaroslav is offline
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Bart. Bend the edges of the sheet metal upside down. The edge will hold its shape. After shape you straighten the shape or cut it. You can better control the shape you make. Not now. It's alive in all directions.
Or you can fasten the angle with clamps or weld points.
DSC097081.jpg
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  #16  
Old 05-05-2021, 07:11 PM
Bart Bart is offline
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Yes I should have done this first but I had already started to wheel.

Quote:
Originally Posted by Jaroslav View Post
Bart. Bend the edges of the sheet metal upside down. The edge will hold its shape. After shape you straighten the shape or cut it. You can better control the shape you make. Not now. It's alive in all directions.
Or you can fasten the angle with clamps or weld points.
Attachment 59894
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  #17  
Old 05-05-2021, 09:25 PM
mastuart mastuart is offline
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Bart how big is the panel you are making? It looks large. Do you have a helper? If the panel is as large as it looks I dont think many here could do it. At one of the first metal meets I went to I wanted help making a roof panel for my cobra daytona coupe. My roof panel is no where as big as yours looks. Turns out that no one there accept Randy had any experience making a panel that big. We tryed making it several times. Randy would come by and tell us to stretch it some more by wheeling it. Told us the sides would come down. Never made it work. I made it in 4 pieces and welded it together. I know enough now to try it again in one piece. Thinking back Randy was right we needed to stretch a bunch more than we did. Dont give up. You can do it.
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  #18  
Old 05-05-2021, 10:47 PM
Jaroslav Jaroslav is offline
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Einforce the edge of the sheet. Best by placing the edge up. Or by attaching a profile 30 x 30 mm with, for example, clamps or spot welds. When you create a profile or bend in the required shape, after shape end remove it. You bend it back to the required size.
If the panel undulates in all directions, you cannot control it. You still feel like you've bent only a little. Suddenly you find out it's too much.
If you strengthen the edges, everything will calm down.
Try the principle on a smaller panel. You will see it immediately.


In this picture, it's already arched a lot. It goes very badly back.
Looks like it's a little bent. It's not, is it bended more than needed ..


DSC09704.JPG



After this bending, you can check the dimensions of the entire panel.
DSC097081.jpg
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Last edited by Jaroslav; 05-05-2021 at 10:51 PM.
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  #19  
Old 05-06-2021, 01:29 AM
Bart Bart is offline
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Ok. I think you're talking about some kind of sheet blank holder (in metal pressing industry) ?? While the part is being formed.
Similar to hammer forming we hold the sheet around the edges while hammering into the cavity?
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Last edited by Bart; 05-06-2021 at 01:31 AM.
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  #20  
Old 05-06-2021, 06:13 AM
Marc Bourget Marc Bourget is online now
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I think it's different than hammer forming into a die. I've heard the sheet blank holder you mention described as a "slip ring" But this controls the metal, much like a thumbnail tool, trapping the metal to persuade it to shrink as the metal is pulled over a radius in a corner, so to speak.


I believe Jaroslav is advocating for leaving an angled ring or flange around your part to "trap" the center so when stretching (by EW for example) the center will rise the material up to meet your sweeps.
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Last edited by Marc Bourget; 05-06-2021 at 06:16 AM. Reason: added the reference to slip ring
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