Demon Core

Building a replica of a device designed to carry the most dangerous object on Earth requires more than just mechanical skill; it demands a deep dive into historical forensics and material science. Adam Savage recently took on the challenge of recreating the Demon Core transport box, a magnesium container designed by Los Alamos machinists in the 1940s to house a 14-pound sphere of subcritical plutonium. While the original core claimed two lives before being melted down, the transport box remains a fascinating artifact of engineering hubris and ingenuity. This project isn't just about making a box. It's about demystifying a process where every cooling fin and rubber bumper serves a specific historical purpose. The goal of this guide is to recreate the transport container using modern materials like Richlite while maintaining the "military-manufactured" aesthetic of the original Manhattan Project hardware. Essential tools and material selection To build a replica of this caliber, the selection of materials is the first critical hurdle. The original boxes were made of magnesium because the metal is transparent to gamma rays, allowing the core to cool without reflecting radiation back into itself. However, machining magnesium is a high-stakes endeavor due to its extreme flammability. For a workshop replica, Richlite—a phenolic paper and resin product—is the superior choice. It is monolithic, meaning it has no grain or texture, finishes identically on all sides, and sands to a smooth, dense surface perfect for paint. Beyond the chassis material, you will need a representation of the core itself. Midwest Tungsten Service produces a tungsten alloy sphere that matches the 14-pound weight of the original plutonium core with eerie precision. Tungsten’s density provides that "unnatural" heaviness that defines the Demon Core experience. For the mechanical assembly, you’ll need a facing mill, a radius cutter for the internal hemispherical cavity, annular cutters for meat removal, and Helicoils to ensure the hardware stays secure in the resin block. Preparing the monolithic block and primary cavity The build begins by transforming raw sheets of Richlite into a singular, solid cube. For a 7.25-inch finished box, start with slightly oversized 8-inch square pieces. Epoxy these together and allow them to cure overnight. Once solid, use a facing mill to square the block on all six sides until you reach the final dimensions. The block must be perpendicular and perfectly flat to ensure subsequent machining passes—especially the cooling fins—align across the faces. After squaring the block, it must be split into a top and bottom section. Because a 14-pound tungsten ball is nearly impossible to lift out of a deep hole, the split should not be 50/50. Instead, aim for a 4/5 base and a 1/5 lid configuration. This leaves the "equator" of the core exposed, allowing for easy handling. Once the block is cut, use a radius cutter to bore the hemispherical seat. Precision is paramount here; the cavity should be roughly 50 thousandths of an inch larger than the 3.5-inch diameter of the core to account for the nickel coating of the original and to provide a clean fit without vacuum drag. Machining the cooling fins and initiator ports The most distinctive feature of the Demon Core box is the array of cooling fins. These were originally designed to increase surface area for heat dissipation. Machining these requires a methodical approach on the mill. Each pass must be measured with identical depth and spacing to sell the "military-grade" look. If a chip-out occurs—common when milling dense phenolics—UV resin can be used to repair the edge before the final sanding phase. On the top of the box, the Manhattan Project engineers included four ports to house "urchin" initiators. These were the triggers for the atomic reaction. Recreating these involves threading aluminum rings and gluing them into pre-drilled recesses in the lid. A skim pass with a facing mill across these inserts will make the seams disappear once painted. For the caps that screw into these ports, utilize an annular cutter to save time on material removal, then thread them on the lathe to match the internal threads of the lid inserts. Hardware integration and the crackle finish No technical build is complete without robust hardware. Use 6-inch cap head bolts and Helicoils for the main hold-down assembly. The Helicoils provide metal-on-metal threads within the Richlite, preventing the heavy lid from stripping out the resin over time. The handle requires a hybrid approach: a core of Delrin for comfort and strength, sandwiched between aluminum side plates and pinned with brass. This assembly should be epoxied together like a high-end knife handle. For the final aesthetic, the historical record suggests both yellow and black versions of these boxes existed. The black "crackle" finish is particularly evocative of 1940s lab equipment. To achieve this, use PJ1 Fast Black or a similar wrinkle-finish paint. The technique requires two heavy coats applied three minutes apart, followed by a bake in a dedicated shop oven at 150 degrees Fahrenheit for one hour. This heat triggers the paint to shrink and wrinkle into the signature tactical texture. Troubleshooting the rubber shock absorbers The final detail involves 20 rubber stoppers used as bumpers to protect the magnesium fins from impact. Historical accounts from Ralph Sparks, the original machinist, suggested using liquid nitrogen to freeze the rubber before drilling to make it machine like Delrin. While this is a classic machinist's trick for differential heating and press fits, modern high-speed drill bits often handle rubber well enough at room temperature if the speed is high and the feed is steady. If you do use liquid nitrogen, beware of leaving the stoppers submerged too long; the thermal tension between the frozen exterior and the warmer core can cause the rubber to literally explode. Once the holes are centered and drilled, press the stoppers into the pre-milled recesses on the fins. This final layer of protection completes the transformation from a simple box to a museum-quality replica of atomic-age history. The value of historical recreation Completing a build like this provides more than just a shelf piece; it’s a tactile connection to the engineers on a desert mesa who were solving the logistics of the impossible. By researching the bench tools of Louis Slotin—down to his Lufkin steel tape and specific multimeter—you build a context for the machine. The finished transport box is a reminder of human brilliance used for both exploration and tragedy. When you lift that 14-pound tungsten sphere out of its Richlite cradle, you aren't just feeling the weight of metal; you’re feeling the weight of the story that defined the 20th century.