I've done a bit of stereo photography, both digital with a Fuji W3, as well as film-based with a 35mm David White Realist and a medium format Sputnik. But I had always pondered on building my own stereo camera.
When thinking about how to do this project, I had several parameters that needed to be considered:
Build it out of components or cameras I had readily available and at low cost
Build it for the optimal stereo inter-ocular distance of around 65mm (the distance a human's eyes are spaced apart)
Be able to trigger both shutters at roughly the same time
Minimizing the effort by not have to do a lot of machining, cutting, welding, etc.
For all these reasons I settled on building this from two Argus A cameras:
Argus As are cheap. I already had an A2B and an original A that both had the same IRC shutters, lenses and aperture irises in them.
If I put the two cameras base to base, it approximates 65mm distance between the two lenses.
The Argus A lens is able to be turned 360 degrees so you can get the two shutter release levers close to each other.
The tricky part is connecting the two cameras. You need to stabilize them as it's really important that the two pictures are as closely aligned as possible to get the full stereo effect. You also need to put space between the bases, as the rewind knob on the bottom needs to be able to turn freely as you advance the film.
I bought a piece of 1/2 inch aluminum bar stock from Amazon which nicely spaces the things so the rewind knob can turn freely. Then I cut it to the right length so that it aligns the lenses directly over each other. Finally I cut the width equal to the width of the cameras. Then drilled two holes all the way through and cut some pieces of plastic from a Tupperware container to brace the back and front.
Here's what it looks like without the cameras. The arrows are just to be able to align the metal and plastic pieces the right way when you take them apart and put them back together again.
The gold standard of software to combine pictures into stereo pairs is Stereo Photo Maker and it's free! At a minimum, you want to use the Auto-align feature and the auto color adjust feature to get the best results.
And here are some stereo pairs taken with the camera. Getting good stereo pictures requires you to compose with a clearly defined objects in the foreground, middle ground and background.
The traditional way to view these is to print them as Holmes stereo cards and then use a Holmes viewer to view them. The modern way is to copy the stereo pairs over to your smart phone, hold it horizontally while viewing and use a 3D viewer. My favorite is the Homido Mini. It costs only 15 Euros and folds up to fit in your pocket.