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Old 02-23-2011, 01:51 PM
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RatRockx RatRockx is offline
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Default How do you make a reverse curve?

So far I have made some fenders and seats. I did everything by shrinking the edges. But now I am looking to make this reversed type of curve, where the edges need to be stretched or the centerline needs shrinking.

Would you go shrinking or stretching and what type of tools would you use to do it? I don't have one of these shrink/stretch-mouth presses. But I think they would be useless anyway since the curved panel wouldn't fit in the mouth.

I hope this simple sketch clearifies the shape a bit.

reverse.jpg
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Last edited by RatRockx; 02-24-2011 at 04:28 PM.
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Old 02-23-2011, 01:56 PM
David Gardiner David Gardiner is offline
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You have to stretch the two outside edges. This can be done in many ways. You can use a wheeling machine, you can block them with a blocking hammer on a block. It is unlikely that the shape will remain constant while you form it yo will have to reshape the curve once you have stretched the edges or create the curve as you stretch the outer edges.

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Old 02-23-2011, 03:07 PM
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Kerry Pinkerton Kerry Pinkerton is offline
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David is completely correct. Reverse curves are the exact opposite of a bowl shape. Shrinking the center of a panel is relatively hard so I normally do them all stretch on the outer edges.

If I were making it, I'd make a Burt Buck (use the search function to find out how) to model the surface I wanted. From there you can make a slit paper pattern which will show you where the metal has to be stretched. You could also make an FSP (Flexible Shape Pattern) to help you but you need a true surface to make the FSP...either the original surface or some type of foam or Burt buck.

I've made a bunch of reverse panels for the roadster and they're always difficult because you have to do them 'backward' from the normal surfaces. They really get nasty when you have a complex surface with both crowned surfaces AND reverses in the same panel. Those will make you loose hair.
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Old 02-23-2011, 03:18 PM
David Gardiner David Gardiner is offline
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[QUOTE= They really get nasty when you have a complex surface with both crowned surfaces AND reverses in the same panel. Those will make you loose hair.[/QUOTE]

That explains it!
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Old 02-23-2011, 10:17 PM
ByronR ByronR is offline
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Hi Joris,

I found this video of a reverse curve by Lazze to be fascinating.
http://www.youtube.com/watch?v=Et5Wh...eature=related
You will note that he also has a couple of other videos of a larger reverse curve created on the english wheel only (less marking).
Google videos will lead you to a number of other videos of interest.
http://www.google.com/search?q=metal...vgc&hl=en&aq=f
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Old 02-24-2011, 04:40 AM
Ram-rod Ram-rod is offline
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Default reverse saddle school work

Someone asked about this shape once before, it was for an assignment for school. A reverse saddle shape was needed maybe it was on metal meet probably lost in the crash there was some good solutions offered back then

I remember the guys asking for extra credit for helping
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Old 02-24-2011, 04:27 PM
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Thanks a lot for the input so far. I had never even heard of the term blocking hammer and a google search came up with a lot of additional info. It's been helpful and I'll give it a try soon.
So much I don't know (yet ).
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Old 02-24-2011, 06:55 PM
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My guess is that you are looking at this sort of problem.

How to make an anticlastic (inside of a donut) curve so you can make smooth transition between two surfaces.

How big of a radius do you need on your part?
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Old 02-24-2011, 08:46 PM
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I did this today on my Mechammer with a linear stretching die
just to show another way
linear stretching reverse 002.jpg

linear stretching reverse 003.jpg

linear stretching reverse 005.jpg

linear stretching reverse 012.jpg
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Old 02-24-2011, 09:17 PM
mark g mark g is offline
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If the part you're making isn't too wide you could try something like this:

Make a forming stake out of a piece of pipe. Put some heat to it and bend it to one axis of your part. Then carve a two lobed anticlastic hammer out of some hardwood which is approximately the profile of the other axis of your part. Lay your metal on the stake and slowly dress it down to shape. Planish the part on the stake with steel hammers to finish it out. I use this technique for the back side of bird necks sometimes.

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