My design is uber-simple and based on a couple of desired goals:
- It has to be doable by me, with my limited (and that's generous) mechanical skills, tools, and space.
- It has to break down into fairly small bits for storage.
- It has to handle books from mass market up to large reference or coffee-table sized.
Most of the pieces roughed out in cardboard or 2x4's in the attached. The top cross piece will be lighter (probably 1x2) and will nest in grooves in the top of the side columns. The side columns will (read: "may someday") hinge to fold in half outwards (meaning the cross-brace will keep the columns from folding during use. The bottom feet are T's whose stems swing in for storage; the columns would fall inward except, again, for the top brace, and the clamps keep things stable during use. There will also be a counterweight on a pulley to nearly balance the weight of raising the platen. The final height of the side columns will be determined by how high the platen goes and how low whatever light I eventually get hangs.
- IMGP7633.PEF.jpg (234 KiB) Viewed 12688 times
I found the cardboard-and-lumber mockup to be very useful for good visualizing. A couple of things that the mockup made clear to me:
- Making the bookrest first will let you keep an eye on ergonomics (in terms of locating the platen handle, and how high you have to lift the platen to get under it to turn a page.) The one I ended up with here is several inches taller than my original plan to accommodate my height; I ended up raising the cameras and the lights too to compensate.
- It's going to be helpful to be able to leave the book as near as possible to the front of the bookrest; the platen won't have to be raised as high. This also means that the lack of rigid connection between the columns and the base is a good thing; the cameras can be moved forward to center smaller books when they're at the front.
- A 90 degree angle in the bookrest seems to be the standard around here but it seems very risky to the pages of the book as you lower the platen; the platen could pull on pages as it lowers and crease them inwards near the spine. I don't think a larger angle will hurt the spine -- probably closer to 110 or 120 will be my final opening angle. I expect this will require that the camera be focused pretty closely to avoid picking up the nearer page, but that's a once-per-book adjustment so I don't expect it will be too bad (especially with the mobile columns.)
Comments? Suggestions? Critiques?
Actually I expect the thing to get smaller; the side columns don't need to be nearly so high, but only building from the bottom up will tell me their correct sizes. 
