This tutorial is going to cover a method for generating accurate metal parts using 3d printed molds, as well as a functional part I fabricated using this method.
I built a camera arm to document projects a few months ago. The joints are clamped down with rubber pads between them to prevent slipping, but I noticed the joint at the base kept creeping down over long periods of time (like while capturing time lapses). I decided to fix it with a locking plate like you'd find on C-stands, but wanted to avoid using a printed part that would chew itself up after a few months of use.
I felt that a metal locking plate would be ideal, and I'd been fiddling around with stovetop casting alloys anyway. The locking plate assembly is just two copies of the same part that have teeth that mesh together to prevent them from slipping past one another once clamped down.
If you're familiar with some of my other casting projects, you might notice that this metal casting process is similar to the one I used to generate the waxes that are part of the Glaucus build.
The broad strokes of the method are that you design the part you'd like at the end in CAD, design a floor under your part with walls around it (I call this a bathtub), print the bathtub mold you designed, cast the mold using 2-part silicone (making sure it's nice and level), and cast your final material into that mold. Once you've got the knack of replicating parts using 1-part molds, you can get fancier: adding vent holes for letting air escape or labels for your parts or building multiple parts for your molds for even more precise geometry.