Sure, post away Daniel!
I'd be honored to see it there. I hereby stamp a CC by-nc-sa license on it.
Brief explanation of some parts:
Yes, the "big finger" joint is just electric tape and a piece of plastic tube. The tube slows the downward movement of the finger. Without that it fell down too hard. Tape is no durable solution of course, but I had to fine tune the distances and angles a lot when testing so that was the way to go at this stage. The finger segment cores are just metal rods. The metal sinker right above the eraser add enough pressure for the eraser to grab the page.
The hardest part was the "small finger". That extra finger is vital, without it the page falls back when the big finger lifts off. The small one is just a big screw with a loop screw on top and a bolt and a lot of tape as joint. There's also a screw in the taped part of the swivel straw to make it stiff. Timing was really tricky. To get it to snap into the book only after the big finger has moved the page enough, then stay there so the page turns over and stays put and finally snap out before the platen hits. For that I tied two wires to the swivel. One pulls it CCW when the platen is near the top, the other pulls it CW when the platen is almost down. The rest of the time both wires slack and so the swivel stays put. But as you can see the swivel still tilts sideways a bit too much at the moment and can easily get uneven. It is the weakest link in the setup so far. I first tried a fixed joint (only allowing circulation and no sideways tilting) but then the (very thin cotton) wires snapped.
But that whole problem occurs only because I don't have separate motors for each moving part. I had no small motors at home and lack electronics skills. But I think (properly timed) motors will bypass that problem. (It will, sadly, also make the movements less snappy and without all the wires the device would lose some of its current Rube Goldberg style.
To later on get a device that can autoscan a whole (thick) book some automatic mechanism would also be needed for both moving the book holder sideways (for the platen to keep hitting center) AND to adjust the big finger slightly since the book's right hand side "page pile" is higher when scanning the beginning of the book and that affects where the finger hits the page. If it gets close to the right edge or to the center then the page grab fails.
The bad news is that I don't have much time to improve the device right now. I'll get back to it some time this summer. But I hope someone else gets inspired and remixes this setup for the better right now!
One last thing unrelated to the page turning: several of the scanner builds I've seen here use drawer slides under the book holder for left/right movement. I didn't have an extra spare slide so I just used two U shaped aluminium rods under it. Then I screwed similar rods to the device "floor board" thereby making a straight track in the space between them. That allows left/right movement (only) and has enough friction to stop accidental side slide. Maybe it's been done on other builds already. But I haven't seen it so I thought I'd be worth mentioning.