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CNC and Machining
I spent more than a year and a half experimenting with different designs for a CNC router using off-the-shelf parts. This is the results of my experimentation: a custom designed Cartesian router with an integrated slotted table, full bed access gantry design, and enough stability to machine non-ferrous metals such as brass or aluminum.
Using nothing but some 9-volt batteries, saltwater, and vinyl cutouts, you can create moderately clean markings with appreciable depth in metals. I show this in practice on bare aluminum here.