Frames form for AC Cobra 427

#1
Hello!
I am a student at Warsaw University of Technology and a member of a scientific association, which is building replicas of cars. Recently we have decided that our next project will be making an AC Cobra replic. Our dream is to bring it off, fully by ourself from scratch (only engine and several other components will be taken from some Ford's car).
We already have the necessary plans for the implementation of the chassis. Unfortunately we have some problems with the bodywork. Relying solely on blueprints, we can not perform mold to the body (it will be made ​​of laminate). Frames are needed - transverse sections of the car body. I thought that based on your work you can do something like that. I noticed that they are very accurate and as far as possible reflect the reality. Therefore I would like to ask for help. Do any of you would be able to perform such simple drawings? It is about just simple cuts across the car body. It is such a thing possible?
As the accompanying pictures, sorry the quality but I can not explain the theory better.
I hope you will help me somehow:)
P.S. Important in all this is to maintain (if possible) to a scale drawing so that you can ultimately do with this elements.
 

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#2
Hi mauy rocketry:

Here are some ref photographs. Hope it will be useful.

This is the FactoryFive MK4 Roadster link:
Mk4 Roadster
 

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#3
Thanks for your interest!
Certainly, these pictures will help, but I miss the most important - the body.
The chassis we have almost finished so that there is nothing to worry about;)

To make a body do we have to "form positives". It is a model of (body) car made ​​in scale 1:1. Material for its implementation is mostly wood and polyurethane foam. To do this we need the so-called frames - body cross section. With several of these consists of a skeleton covered with slats him and then polyurethane foam. The biggest problem we have with these frames about how exactly does redraw the shape on the paper would then be able to cut them in wood. I noticed that you have the body very well mapped in 3D so I wonder if you can draw from this a few images in 2D. As the accompanying photo.
 

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#4
Sounds like a cool project!
Unfortunately I have limited modeling skills, but I do have _some_ experience:

It _is_ possible to extract cross-sections from a 3D model. It easiest to do this using a NURBS format model, like this one:
http://www.3dexport.com/3dmodel-ac-cobra-28922.htm#ad-image0
NURBS models are effectively made of cross-sections, called "isoparms".

It is possible to make cross-sections using a polygonal mesh, but it is more difficult and less mathematically accurate.

When I was at university, some of my fellow students helped to create negative forms for a carbon-fiber body built by some engineering students for the Forumula SAE competition.

The body was modeled in Rhinoceros 3D ("Rhino") in NURBS format.
The cross-sections were used to create milling patterns, and a CNC milling machine was used to mill the cross-section patterns out of 2" thick slabs of foam. The foam slabs were then glued together by hand, creating an accurate but rough negative form.
The team encountered a problem here: there were seams between the foam blocks, and the glue in the seams was harder than the foam itself, which made hand-sanding and finishing the inside of the form quite difficult.

So, in order to make an accurate body, you will require A. an accurate 3D model and B.the ability to "finish" the form smoothly without losing accuracy.

The problem is that most 3D models are made by using photos for reference, and the models are not dimensionally correct.
The absolute _best_ way to get accurate measurements is to get a 3D scan of a real Cobra body. This might be difficult, or impossible.
Scans of model cars or toys probably won't work--they are also inaccurate.

Once the wooden frame is built and the foam applied, a "styling bridge" could be built to allow accurate transfer of measurements to the body, as seen in this photo: Clay styling bridge - ACD Museum | Flickr - Photo Sharing!
It's old technology, but it worked successfully for car designers for many, many years.

The fastest solution would be to make a wooden frame based on cross-sections taken from a 3D model (the frame will need to be reduced in size to leave room for the foam layered on top), apply the foam, and then use a 5-axis CNC milling machine to mill the entire body, based on a computer milling file that could be built from the 3D Cobra mesh.

I'd suggest downloading or buying a 3D model online, and testing it to see if it looks "good enough" and if it fits around your frame. Then, if the model is good, extract cross sections in a program like Rhino or AutoCAD.
Programs like Rhino and AutoCAD can "offset" lines--this could be used to generate new cross-sections that are smaller and allow room for the layer of foam on top.

Good luck, I am curious to see what solution you arrive at!
 
#5
I just thought I would post another comment:
I tried downloading a free 3D Cobra mesh and had a look at it. It had the right general shape, but wasn't especially accurate. I was reminded why dimensional accuracy is important: if the body is not accurate, then the windshield, headlights, taillights, and other pieces of hardware will simply not fit.
 

TwoOneOne

Administrator
#6
first of all, sounds like a cool project! so, good luck with it.

It _is_ possible to extract cross-sections from a 3D model. It easiest to do this using a NURBS format model, like this one:
http://www.3dexport.com/3dmodel-ac-cobra-28922.htm#ad-image0
NURBS models are effectively made of cross-sections, called "isoparms".
the mentioned model most likely is not a Nurbs model. I checked out the link and it says it was modeled in Cinema. And Cinema can´t do Nurbs. It has something calld Hypernurbs which is basically a meshsmooth and has nothing to do with "real" Nurbs. So i wouldn´t bother spending 35$ on that.

Cheers
 
#7
TwoOneOne--ach, I should have looked more closely at it. Thanks for the clarification; NURBS and Hypernurbs are two rather different things.