I use shapeways stainless steel 3D printing to make parts for physics experiments. It's only useful when the parts are small and can have sloppy tolerances. But in these cases it saves a fortune. I recently had a dozen small parts made for $200 that would have cost $1000 made by conventional machining. You can make screw threads (1/4 - 20 and larger; 10-24 might work) by printing the thread and then chasing the printed thread with a die or tap before use.