More for visual FYI purposes (spendy) but these have always fascinated me. Basically you make a 2D pattern which is temporarily mounted relative to the metal blank. Then then the tracer mechanism basically copies it as you traverse the work. It a bit more complicated then that because you are making successive feed passes just like regular machining & that's where the hydraulic following comes in. I guess you could say 'analog CNC' Good for complicated or ornate work or even multiple copies of the same thing. Keith Fenner has some vids of his in action.
https://www.kijiji.ca/v-power-tool/...h9WuvU-B0LTqSFvJj-Pj-jT61D-OsKhFR2wtNLLCHGeD4
https://www.kijiji.ca/v-power-tool/...h9WuvU-B0LTqSFvJj-Pj-jT61D-OsKhFR2wtNLLCHGeD4