What you end up with is a homemade foundry flask cast in aluminium from 3D printed modular patterns that slot together. The finished piece is two identical rectangular frames stacked one above the other, and the inside walls carry repeated vertical ribs. Because the patterns come apart, they can be rearranged and reused as needed.
The maker, Julian Makes, modelled the patterns in Fusion 360 and printed them in PLA on a kit-built Prusa at home. Going modular seems a smart call to me, since the printer bed is quite small. The lime green printed patterns sit alongside the cast aluminium sections they produced. Sections are joined with hex head bolts, washers and nyloc nuts, and the hardware list runs to 8 mm steel bolts, chandelier tubing with a 6.5 mm bore over a 6.5 mm steel rod, and threadlocker. Alignment pairs a pin and hole on one side with a pin and slot on the other.
The finishing work stands out. A green printed guide template was clamped over the corner flanges to mark hole centres, with scribed layout lines, then an automatic center punch and a drill press put the holes in, stepping pilot holes up to a final 9 mm. Cast surfaces were ground with an angle grinder and the corner joints filed by hand at 45 degrees. Four sides were bolted finger-tight to check corner alignment. One drill bit snapped along the way and was cleared out only after a delay.
This is a version 6.7 prototype, and it is not a finished story. The maker admits the flask could be flatter without fancy tools and that one pin is slightly wonky, and it has not been used yet. Version 6.8, with interlocking corner tabs, is untested, and the files were due out within a week or two. A bought flask at around £300 seemed small, and the stated aim is DIY fun rather than saving money.
Project by Julian Makes. Watch it on their YouTube channel: