Made a little tester to see if I could use something besides the flat hinges we carry at the store. Ideally I want a box that reveals nothing of itself to the outside and visible hinges don't work with that.
The original try was simply an elbow shape and it doesn't work. It sticks just after I start turning. So I thought to add a pivot point so the radius of the turn can increase as much as I need it to.
Rough but it works! If I find time I'd make a perfect little pair of templates for my linkage.
These kind of hinges will be what I use on my drawing easel box.