Creative craftsman Seth of Robinson Foundry makes things out of metal that would be difficult or impossible to machine the traditional way. As an example, these bolts with zigzag threads:
He then struck upon the idea of creating a rather unique maze, or a sort of three-dimensional combination lock:
The point is to get the nut, which has a protrusion on the inside, all the way along the shaft by rotating and advancing it:
So how did he make them? Using the lost wax casting process, but with PLA rather than wax. After designing the shape in CAD, Seth 3D-printed models of both the nut and bolt.
"Then I coated the models 10 times with a ceramic material called Suspendaslurry," he writes. "After the ceramic shells were completely dry I placed them in my kiln and melted out the PLA plastic.
"At 1500 degrees Fahrenheit the ceramic shells became vitrified, turning into a ceramic that can withstand the heat of molten bronze. I melted the bronze in my homemade keg foundry furnace and then poured the liquid metal into the ceramic shell molds."