In our Aggregate.Org / University of Kentucky research exhibit at the IEEE/ACM Supercomputing 2013 conference, we had a number of 3D-printed things in the exhibit or used as giveaways. This is the little dovetail puzzle keychain that we made as a giveaway to remind people of how our SWAR (SIMD Within A Register) and LAR (Line Associative Register) technologies work. The dovetails on the top and bottom appear to interlock such that it would be impossible to take apart... which it isn't.
SWAR & LAR are computer technologies in which registers are partitioned into fields that are operated upon in parallel. We also have posted a blank version of this puzzle keychain for folks who don't care about SWAR & LAR but like the apparently impossible dovetailing.
We wanted to make an interesting giveaway that would remind people of how our SWAR & LAR computer technologies work. The design is a combination of the 1990s SWAR logo (shown above) and the well-known trick used in Thing 81904. Unfortunately, Thing 81904 has only two parts; it takes at least three to convey the idea of subdividing into multiple different-sized fields, and the angles used in Thing 81904 would not allow a middle piece to be printed without supports. Thus, we created a design that is easily printable with all parts laying flat. The design has three segments (a middle and two ends), but could be trivially extended to as many parts as desired.
The parts are plated together for printing as a set, but are not printed assembled because separate printing allows a tighter tolerance without binding. Tighter tolerances cause more friction, which enhances the illusion that the parts cannot be separated. We suggest printing sets in three different colors and then mixing the colors in assembly -- which really challenges tolerances a bit more because minor variations in filament diameter can make some colors print with slightly different dimensions. We also found that we could print these parts at over 100mm/s on our MakerGear M2, but tolerances had to go from leaving a 0.3mm gap around parts up to 0.4mm. Your tolerances may vary, and that's why we have included part sets at 0.2mm, 0.3mm, 0.4mm, and 0.5mm tolerances with filenames containing 02, 03, 04, and 05.
Our prints were made using 0.25mm extrusion of PLA with 2 walls and 5%-25% fill on a MakerGear M2. There were no difficult-to-print areas, but tolerances with some filaments were held a bit better with fill at least 20%.