We've been loving our CNC and we've made so many things. One thing we need to improve on is nesting designs to minimize waste, so to reuse the scrap aluminum, we built this electric foundry to melt the pieces into an ingot that can be machined again.
The whole build cost about $200, and on our 120VAC home circuit, the calculated power of this foundry is about 1.6kW.
⚠️ Safety warning
This project uses high voltage power supplies and presents a serious risk of personal injury. The heating element is live when in use and may hold electrical potential even when shut off. The foundry reaches extremely high temperatures and produces molten metal, both serious burn hazards. Use proper precautions, safety gear, and consult an experienced professional.
Materials list
Insulating fire bricks (soft type), furnace cement, crucible tongs, ceramic terminal blocks, high temperature wire, a baking pan, a graphite crucible, a K-type thermocouple (0–1300°C range), heating element coil wire, a PID controller, 1" angle iron, a 125/250V toggle switch, and 14 gauge power cord.
Construction
Brick assembly
We started with 10 insulated fire bricks (soft fire bricks insulate better than hard varieties) and arranged them into a simple top-loading box to house the crucible. Two bricks were cut lengthwise in half with a Japanese pull saw to fill the corners.
Heating element grooves
We measured three evenly spaced lines from floor to rim around the interior perimeter to mark where the coil would sit, then filed grooves into the bricks with a square file, using a scrap piece of coil to check depth. The walls were bonded together with furnace cement. After a couple hours of cure time, we drilled holes for the heating element inlet and outlet, then bonded the final walls.
Metal frame
We cut 1-inch angle iron to fit along all outside corners for structural reinforcement, so the brittle bricks wouldn't break during movement, TIG welding the joints as simple lap joints rather than mitered connections.
Electrical system
The control system uses a PID controller, a solid state relay, thermally insulated wire, and the K-type thermocouple. We 3D printed an enclosure and mounted a toggle switch and an outlet salvaged from an old computer power supply, wiring everything per the PID controller's directions with two long pigtails connecting to each end of the heating coil. The enclosure bolted to the metal structure.
Temperature monitoring
We drilled a hole for the thermocouple, positioned about 1 inch from the tip for accurate floor readings, with a small adjustable arm fabricated to mount it.
Heating element calculations
Using steel wire coil as the heating element, we calculated a resistance of about 9 ohms:
- Current = Voltage / Resistance = 120V / 9Ω = 13.3 amps (well under the 20-amp circuit capacity)
- Power = Current × Volts = 13.3 amps × 120V = 1600 watts
Coiling around the foundry three times for even heat distribution required 78 inches of stretched coil.
Coil installation
After stretching the coil in a bench vise, we placed it into the grooves and secured it with straightened steel wire staples. The coil ends protruded through the drilled holes and connected to a ceramic terminal block screwed into the brick.
Results
The foundry took about 20 minutes to reach 900°C and about 15 minutes to melt small aluminum scraps, a rewarding project that combined welding, 3D printing, and electronics into a genuinely useful tool for our CNC scrap.