Prompted by a fellow 3D printing user's comment "I wish there's something we could do with these spent spools" I decided to investigate a project idea that's been sitting in the back of my head: a dynamically reconfigurable storage system which uses a spent 3D printer filament spool as its structural core. After setting a few goals to give me a direction, I designed the trays that I wanted to fit within these spent spools.

As a starting point I quickly whipped up a pie-shaped wedge solid shape in CadQuery, then I fed it into my 3D printing slicer to be printed in vase mode. Also called spiral mode, or sometimes single-wall mode. Whatever the name given by a particular slicer program, the result is a shape with a single-width wall the thickness of our nozzle diameter. It is very frugal with filament use (one of my goals of this project) but the thin wall raise other challenges. The first is structural. It may be hard to see in the above picture, but the flat sides of the first test tray is bowed instead of flat. The inner and outer curved sides fared better because the tiny bit of curvature gave them enough strength to maintain shape better than the flat sides. To solve this problem, I needed to add small ribs along the flat sides to give it a similar level of structure, and beveled edges top and bottom for additional strength.

Once I had flat sides that could stand on their own, I investigated the second vase mode challenge: strength. There just isn't very much plastic to hold together, and it is possible to rip a vase mode print apart with our hands. I estimate the strength to be roughly the amount of force we'd need to rip a hole in a sturdy plastic bag. So they're not tremendously strong, but I think they're strong enough for light duty use.

But I didn't want to restrict my system to light duty use. We all have our mental organization models, and it would be inconvenient to have a system that breaks down when something is a little to heavy to be stored alongside similar items. To address this possibility, I modified my CadQuery script so it could generate trays with thicker walls for more strength. The exterior dimensions remain the same. The idea is that we try the frugal vase mode tray first (lower tray in picture) and, if that should fail, we can print a replacement tray with thicker walls (upper tray in picture) which can sit in the same slot.

Another subject of evolution is the front handle. The test tray has no front handle, which obviously won't work. (Side note: in above picture, the supposed-to-be-flat sides are more visibly bowed.) I tried a few handle design ideas, keeping in mind the shape had to be amenable to vase mode printing. After a few iterations I settled on a small handle in the middle of a spherical depression, almost like a small stack of coins, that my fingers could easily pinch to hold and manipulate the tray.

While I evolved the tray design, I was also evolving the mechanism to hold these trays in place.

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