I designed and fabricated a weird 3D printed 4-axis CNC machine (in ~3 months, oof) which uses carbide inserts to carve tiny isolation routes in chunks of PCB substrate. It's very much a finicky proof-of-concept, and may very well host fatal hidden gremlins which doom the project to novelty status, but with a bit of care I can produce boards with 6/6 design rules (0.15 mm spaces and traces) at 20-30 mm/s, roughly an order of magnitude faster than a desktop mill with significantly less noise.<p>I gave a talk this weekend on the machine at the eighth Hackaday Supercon, which will be on YouTube at some point, but for now here is a link to the project page, including design files and a few dozen hasty project logs.