I’ve done box joints before, just once, for a 3D picture frame celebrating a newborn baby. It was a harrowing experience back then because I didn’t really understand how the width of the laser beam affects the ability of two pieces to fit together and because I was using a thick wood that just didn’t want to play nicely. The piece did turn out fine, but the procedure was such a mess that I haven’t really considered box joints since.
That changed this week, because Tetris was still on my mind. At some point while laying out hundreds of tiny tetriminos for the NES etching project I realized that it shouldn’t be too hard to recreate those popular shapes in 3D if I could just get over my box joint demons. Wood was out; I selected varying colors of 1/8″ thick acrylic for my material this time.
Figuring out the shapes initially took no time at all. I settled on 1″ squares to form the basic tetrimino shapes and made sure that the box joints (the teeth shown above) were the same thickness as the material, 1/8″. When I began on the Cyan I, there were no inside corners and the design went incredibly smoothly. Because Yellow O, unpictured, is just a fatter version of the same shape, adjusting the cut was trivial.
When I got around to Blue J and Orange L, I had to get through a few bad test cuts before figuring out how to adjust two shapes to account for the inner corner. Once I discovered how it should be shaped, the same inner corner treatment could be applied to Red Z (shown here) and Green S, as well as the unpictured Purple T.
With that design puzzle solved, more test cuts were spent discovering the best kerf setting for this material. After cutting a few box-jointed pieces that wouldn’t fit together and a few that fit together so loosely they’d require glue, I discovered that the laser’s width burned away 0.0064″ of material on each line, which could be solved with an offset path setting of 0.0032″. The resulting graveyard of pieces shows many cracked edges, but the final pieces fit together so perfectly that they’ll never fall apart by accident.
Speaking of accidents and graveyards, don’t soak transfer paper in Goo Gone. One of the fun little extra steps I took during this weekly project was to vector etch a pattern of tiny tetriminos over top of these big 3D pieces. Well, when you vector etch a sheet of acrylic that is covered with transfer paper to prevent burn issues, you end up with hundreds of tiny little paper shapes you then have to remove by hand; you can see them here in the comparison between Orange L and Blue J. I thought I’d save time by liberally applying Goo Gone to the paper surfaces and then leaving the pieces overnight. I figured I should be able to just wipe away the paper, its adhesive dissolved.
The end result was horrific: the Goo Gone did make the paper very easy to remove, but it left the adhesive on the acrylic, which had become a horrible, gummy mess. Way too much time was spent using more Goo Gone, some isopropyl alcohol, and some plain liquid soap to slowly remove the residue from the etched pieces. What a mess.
Most of my tetriminos were cut out of transparent colored acrylic, though some pieces (shown in the graveyard pictures) were opaque. The Cyan I was the most fun to look at, thanks to the “Ice Blue” acrylic used. It didn’t have much visible color looking at the surface of the material, but the cyan color really shines through the etches and cut edges. It appears to glow, even when placed next to the other transparent tetriminos.