Weinberg points out that even before consumer 3D-printing became fashionable, gun enthusiasts were already making their own metal firearm components with computer controlled milling machines and posting their designs to sites like CNCguns.com.
This configuration should be cheaper than many other eye-controlled solutions out there, as the components are integrated directly into the computer and no external hardware is needed.
Unfortunately, these chains come in several varieties, and making useful materials from them requires that the amount of each variety in the mixture be controlled, as the properties of the resulting material depend on the proportions of its components.