IC Puzzle

This is an IC puzzle created as a 3D-printed handout for the University of Kentucky Department of Electrical and Computer Engineering, which is why it has the UK logo on the top and ECE on the bottom. Note: there is now an improved version of this.

Where did this puzzle design come from? A polished cast metal version of this type of puzzle called “Magic Wands” is widely available from online sellers. A 3D model matching those was created by Joseph Escalona as CPU Puzzle, and he states that this puzzle was originally machined out of brass by Rocky Chiaro in 2004 as the AB-L puzzle. It is probably written up in Chiaro's 2020 book “Puzzle Sculpture,” but I haven't been able to confirm this. In any case, my design was created from scratch for 3D printing but does employ the same puzzle logic.

The designs here are intended to be printed as nine pieces which, when assembled, produce a 48x48mm completed puzzle. Print time per puzzle is around half an hour when making a bunch on my Bambu X1 Carbon and printing the pins separately from the IC bodies to minimize the number of filament color changes. There are two versions: the original version is 240303 and there is also a slightly simplified 240305 version that prints a little easier and faster. The 240305 version uses a rectangular pin profile instead of the original version's compressed octagonal cross section.

There are 8 “pins” passing through the IC. Unlike the “wands” in the other puzzles, these pins shaped so that they can be printed flat on the printer bed.  This shape also makes the pins significantly easier to keep oriented correctly when assembling the puzzle because they can't spin, and they even look much more like the pins of a typical IC. The pins of an IC would not stick far out of the IC body, so neither do these. Another subtle difference is that one of the wands has no cuts, which means that it can fall out unless externally held in place. My design instead places a flexible bump on the center of that rod to cause sufficient friction to hold it in place – a simple example of a conformant material structure taking advantage of the ability of plastic to flex a little. Here I used gray PLA for the pins, although metallic silver silk PLA might be a better choice. All the pins are in an easily printed orientation in ukece*_1.stl. Especially if you print with a brim, you might need to clean-up the bottoms of these pins a little bit; they shouldn't be a very tight fit in the IC body.

The 9th piece is the IC body, which can be printed in two colors so the UK logo and ECE text on the other side stand out from the body; I used metalic blue silk PLA and black PLA. The body is ukece*_2.stl and the logos are ukece*_3.stl. The IC body design isn't particularly clever and is symmetric, so there are four placements of the pins that can solve the puzzle. There are internal spans in the IC body, but they are all short enough to be handled without supports on every printer I've ever used.

Oh yeah. How does one solve the puzzle? Well, taking it apart is pretty easy once you've discovered which pin doesn't have any interlocking cuts. I've included a partially exploded image showing the number sequence for removing the pins. Note that 6 and 7 are identical and thus interchangeable in this order. To reassemble, simply install the pins in the reverse order, starting with 8. None of the pins are numbered as they print, so if you don't want to be told the solution, don't match pins up to the numbering on the image.