UK ECE Lightbulb Puzzle Keychain

I am always trying to come up with interesting little 3D-printable puzzles and wanted something appropriate as an Electrical and Computer Engineering Department give-away for the University of Kentucky's College of Engineering E-Day 2024 open house.

The idea that a lightbulb might be a good abstract representation of ECE seemed reasonable, so I started by creating a model of one. After several tries, I found that BillyBigStuff's Lightbulb Light Pull had a somewhat more credible shape; while this isn't exactly a remix of that, I did model my lightbulb's overall shape after it. My version also uses a 45-degree screw thread based on Dan Kirshner's thread library. However, the real point of this is the puzzle aspect, which is entirely mine, as is the embedded UK logo.

I tried several other (significantly harder to solve) puzzle designs, but the problem was always that the puzzle wouldn't hold together well enough to be a useful keychain: this design does. The 5 main parts of this puzzle make up the glass of the lightbulb, which I print using natural (clear) PLA. By themselves, they don't hold together well enough, however, the screw thread of the 6th part, which is exposed at the bottom of the bulb, actually runs all the way through the puzzle. Thus, the puzzle pieces are literally screwed into place and cannot be taken apart without unscrewing them first. Ah, but there's another trick: although the exposed thread is printed in metallic silver PLA, the portion of the thread that's inside the bulb is printed using glow-in-the-dark filament. Thus, if you hold the bulb in bright light for a bit, it will glow from inside when moved into darkness – rather like a lit lightbulb!

The assembled STL is just to show how it all comes together, not for printing. Basically, you start with the 0a part, stack 0b on that, then 0c on that, then 0d, then finally 0e1 – that gives you the glass part of the bulb. Then you simply screw part 23 into that assembly, locking everything together. A standard 25mm diameter keychain ring can be put through the hole in the bottom of the thread. There are a total of four PLA colors used: natural for 0a, 0b, 0c, 0d, and most of 0e1; blue for the logo on 0e1; silver for the bottom of 23; and glow-in-the-dark for the top of 23. If your printer can't handle two-color printing, I recommend printing 0a, 0b, 0c, 0d, and 0e1 all in natural, then using the pause-and-change-color method to print 23 in silver and glow. You'll probably want to print with a brim for parts 0a and 23; I didn't need to using the cold plate of my Bambu X1 Carbon, but it was needed if I used the texture PEI plate instead. The only unsupported span is in part 0e1, and it's a very short internal span which is not a problem if printed a little sloppy. As I printed them, a completed bulb weighs just 8.5g, or 10g including a 25mm metal ring.

Well, that's all there is to it. Enjoy! It's a very easy puzzle once you realize you need to unscrew the pieces to disassemble it…