Turning 3D Prints Into an Iron Wrench With a Microwave

Thanks to 3D printers, we can now manufacture custom replacement parts, household tools, and all sorts of other useful items right in our own homes. This has been a huge boon to hobbyists, in particular. Shoddy handmade parts and enclosures are now being replaced by professional-looking, high-precision components that rival the quality of industrial injection molding.

Despite these advancements, 3D printers do have their limits. For the most part, they can only work with relatively soft materials, such as plastics. That’s fine for many applications, but when greater strength or heat resistance is needed, a 3D printer isn’t going to get the job done—at least, not without the exotic equipment found in research labs. It is unlikely that printing in metal will come to the masses any time soon.

If Denny of the Shake the Future YouTube channel is right, there may be a stopgap solution for making metal parts. In a recent video, he showed how it is possible to cast a fully functional adjustable wrench out of iron using little more than a standard 3D printer and a microwave.

Microwaves are not known for melting metal. In fact, placing bare metal inside one is a pretty terrible idea. But Denny’s process takes advantage of a clever workaround: silicon carbide. By fabricating homemade silicon carbide crucibles and rings, he creates a setup that absorbs microwave radiation and converts it into intense heat. Enclosed in an insulated chamber — effectively a DIY “microwave kiln” — the system can reach temperatures high enough to melt iron.

Denny begins by designing the wrench components — the handle, movable jaw, thumb wheel, and retaining pin — in CAD software and 3D prints them in PLA plastic. These printed parts are not the final product but sacrificial patterns.

Using a mixture of fine silica sand and sodium silicate, he packs molds around the prints. The molds are then cured through a combination of freezing, oven heating, and low-power microwave curing. Once hardened, the plastic patterns are burned out inside the microwave kiln, leaving hollow cavities ready to receive molten iron.

After preheating scrap iron, Denny places it in the silicon carbide crucible and returns it to the microwave. When the metal liquefies, he carefully pours it into the prepared molds. The results are surprisingly clean castings, complete with small internal holes formed by tightly packed sand cores.

Once cleaned and assembled, the wrench looks like the real deal — although minor fit issues, such as an overly loose jaw and a slightly wobbly thumb wheel, hint at scaling and finishing missteps. But the real test comes when torque is applied to a bolt. Under load, the cast iron jaw snaps.

That wasn’t exactly the desired result. The reason for this is that while the microwave casting process works, cast iron is simply too brittle for the thin, high-stress sections of an adjustable wrench. Denny suggests that a future version made from carbon steel, perhaps sourced from melted rebar, could yield a tool that is far more durable.

Keep in mind that Denny is an experienced metalworker. If you are not, then you definitely don’t want to try this method at home.