I thought it would be cool to reuse spent 3D printing filament spools as the core of a storage system. The storage trays can be configured to be within a range of sizes. Each could be printed either with filament-efficient single-wall vase mode for light duty use, or with thicker walls for heavier duty use. I explored a few ideas on how I might design a self-contained system using interlocking trays, but I quickly gave up on that idea. Fundamentally, these trays form a circle around a spool. And when one tray is removed in use, something has to keep the rest of the trays in place. In my design, that something is the tray base which will stay behind when the tray is removed.

To keep the storage system modular, every tray will have its own corresponding base. All the bases will clip together into a complete ring that encloses the inner diameter of the spool.

How will that base keep the tray in place? My first attempt used small clips that reach from the inner ring out to the outer radius to keep its tray in place. This worked for a small tray, but it failed for larger trays. Each little clips has a fixed amount of holding power and it wasn't enough for the larger trays. And even when it worked, it was not very satisfactory. Ideal CAD doesn't translate to real world 3D print all the time, and such small errors meant the clips were unreliable and difficult to use.

Those clips then evolved into a small loop to keep the tray in place. The loop helps keep the base in the intended shape, and the loop also has holding power directly proportional to the size of a tray because a loop gets bigger as its corresponding tray does. I'm still trying to be frugal with filament, so I started with thin loops (pictured) that didn't work before increasing their thickness until I had a reliable and satisfying tray retention mechanism.

The inner ring also underwent several revisions. It may look like a simple tab and slot mechanism, but it took more fine-tuning than I had expected before I had a satisfactory system. The main theme was the fact I wanted to minimize filament usage, so the inner ring was as small as I could make it. Which meant it didn't leave much room for the tab and the slot. Tabs that are too small tend to break off rather than hold as intended. This design is the smallest tab size that worked reliably, and the smallest ring that I can fit around the tab and slot of that size. Since these factors are a function of strength of 3D-printed plastic, I think it's better to keep them the same size instead of dynamically changing in response to configuration parameters.

Source code for this project is publicly available at https://github.com/Roger-random/r2s4