I have a suggestion. Don't laugh...
Originally Posted by dkirker
I know we live in a wonderful digital age, but If you lack top end 3D scanning technology, you could measure and draw the part. There are ways to calculate the centers of curves and such. Of course, depending on complexity, this might be quite a job.
Would this work as a 'lower tech' shortcut?
1. Lay the part flat on a document scanner and scan.
2. Stick that scanned surface to a small block of wood (or whatever you have) that is roughly the same surface size, but will support the object.
3. Now you can lay the block on it's side and scan the side elevation of the object. Likewise, you can do the ends, moving the part if the block isn't the perfect size.
4. Import the images to a CAD program and trace the edges as elevations. This will create at least a rough model you can improve. It's likely the scanner resoultion is comparable or better than 3D printing resolution.
* This will hopefully scan the contacting edges accurately (check this), but where the part curves away from the platten, there will be slight distortion and possibly lack of focus, so these areas will have to be corrected by measuring.
* If the part material is flexible, it will need to be held in the correct shape as it will be on the phone - easier if it is rigid.
Of course, a better image can be obtained with a camera, but then you have to account for lens distortion. In film effects, this is done when altering live action shots, but I believe they shoot a known object or chart with the actual lens, then the computer can calculate distortion and alter it's rendering to match existing footage - you maybe don't have those resources. For areas that won't meet the scanner surface, you could place an accurate measure at the plane of the internal surface and photograph. Then size the image of the scale in the CAD program to match it's measurements.
The above might be enough to get images of a simple object that you can use to create a 3D model. If not, there's measuring & calculating..... BUT!
Depending on where you live, There's a good chance there is a community workshop. What's the trendy name? Maker spaces?
There might well be a decent 3D scanning and printing setup there that you could use. It makes all the elaborate messing about with 2D scanners redundant - I have a bad habit of coming up with complicated ways to do simple things! ;-) But I'll leave it there in case you want to do it all yourself and fancy a challenge.