BTW, there is one other problem with this system that needs some engineering effort. It will work fine as it is, but eventually we need to solve this thing. I'm going to update this post with this design challenge soon, and provide images, but for now I am going to try to explain it primarily with text since I am posting from a phone.
On the cradle, the area where the spine of the book rests is flat. On this design, there is a 1/2" channel to accept a dowel. The idea of the dowel is to support the spine of the book as it curves up from being open. This works fine when you are in the middle of the book.
However, on thick books, the thickness of the curving stack of pages changes the inside angle of the book with respect to the platen. The end result is that the book does not perfectly self-center. When you are at the left or right extreme of the book, the off-centered-ness can be up to 1/4", which is detrimental to the overall scan quality.
Right now, this can be fixed by installing toolbox liner and pulling on the sides of it to rotate the spine of the book slightly in either direction as the scan proceeds from the left to the right of the book.
Mechanically speaking, the solution is a spine support that can rotate the spine a few degrees right and left from the central pivot point of the spine, longitudinally along it, like a super-wide teeter-totter. Maybe some skate-bearing thing can be cooked up... it is only necessary for larger books, so I'm realizing as I write this that it's entirely possible to have it be a drop-in-insert.
