Transforming snowflake/Chirstmas tree ornament

Update: I have added a new 1.5 version of the model (scad, stl, and gcode files). I redesigned the base part and I believe it works better in every way. 

This ornament prints flat in a snowflake-ish shape, and can be hung up as a snowflake, or finagled into a 3-dimensional tree shape.

I was originally inspired by pop-up cards and books and wanted to make something similar, but using hinge-like structures instead of folds in paper. Of course, the hinges have to have a much bigger radius, so there are quite a few interesting differences.

This was made in OpenSCAD, and I separated the design into two parts: a library of sorts for making these fold-based structures, and the tree design itself.

The library is called “manhattanish” because the way that these folded structures work reminded me of the concept of Manhattan distance: in order to get from point A to point B in Manhattan (or any other grid-like space), you have to go some set number of blocks in the east/west and some set number of blocks in the north/south direction, but it doesn't really matter in what order or how you break it up. 

This is similar in a folded structure with hinges, except there are three distances which must be the same if you want to get to the same “point”: the vertical travel, the horizontal travel, and the total hinge length. 

Printing

Since this model includes living hinges, it's intended to be printed using PETG. I did a back-of-envelope calculation for how long the hinges should be to not exceed “elongation at yield” for PETG, which I took to be 3% based on some googling. This may or may not work well in other materials.

I included a gcode file that was sliced in Cura with the following custom settings:

Enable bridge settings: true

Bridge has multiple layers: false

Bridge wall flow: 110%

Bridge skin flow: 110%

Bridge  wall coasting: 0

Build plate adhesion type: skirt

Line width: 0.3 (yes, on an 0.4 nozzle. Precision is an illusion anyway.)

The bridge settings are a bit “backwards” from normal, since my main goal was to have a strong and mostly coherent single-layer bridge, and I didn't mind if some sagging happened.

The line width is also intended to “squeeze in” some more lines per bridge. 

Putting it together

In my experience, the trickiest part is getting the thing off the print bed without breaking it. I just try to go slow, use a scraper to get under each part that's on the bed separately and pop it off gently, going around in a circle, and doing the middle piece last. Maybe if you have a nicer print bed this won't be a problem though.

Once it's off the bed, it's relatively sturdy and much less likely to break.

To get it into the tree shape, I start with the trunk and the “branches” in the middle. Each trunk pieces has two branches, one higher and one lower. I take two of the trunk pieces that are next to each other, and put them together so the higher branch is going over the lower one. Then continue around the tree. 

After the first step, you should have the trunk in a loosely conical shape. The branches do overlap each other even past their immediate neighbors, so you next you have to keep overlapping the next set of branches, with the topmost one still on top. When it's together, each “top” branch should pass over two “bottom” branches. Once you get there, it stays locked in pretty nicely.

Then I start getting the bottom together. In the new 1.5 version, the two bottom pieces should lock together smoothly if you bring them together slightly angled and then twist to lock. 

When you're putting the bottom pieces together, make sure you're putting the correct sides together. The two sides that should go together (and overlap once locked in place) have a slightly smaller thickness than the opposite sides.