Notebook / Journal Collection - Multiple Sizes

I am pleased to release my very first original design! With back-to-school time upon us, I wanted to make some fun 3D printed notebooks for my six-year-old daughter to practice writing. This project started as an exercise in learning OpenSCAD, but rapidly evolved into an obsessive quest to solve some of the usability challenges I have encountered with other notebook designs. My specific goals included:Flat, thin cover for a slim profile and filament-efficient print.Cover printed face-up to allow for vector artwork to be layered on top.Sturdy hinges that would not easily break when being lugged around by a child.Secure reloadable binding using only 3D printed parts (i.e., no elastic bands).Modular components that can be easily swapped out if one small part breaks.Designing with all these goals in mind was quite a challenge! My first obstacle was the conflict between cover thickness and hinge sturdiness. The hinges need to be much thicker than 2mm, which makes them awkward to integrate d