Take for example these lock levers from my 1962 Valiant. The originals are a diecast aluminium and feature a very fine spline. I doubt they would be able to be manufactured any other way. Even with CNC machining I imagine the part would have to be made in two pieces if it was possible at all.
The replacements were needed due to an oversight on my part. I had made some lovely new door trims for my the Valiant. The fronts turned out so well i went ahead and made the rears to match. However in my enthusiasm I did not take into account the lock levers which only feature on the rears. Show here is the locking lever spline protruding through the trim baseboard before trim, and after I had finished the trim with the padding. No spline protrudes and therefore the original lock levers do not fit. So how to fix this without remaking the whole door trims?
3D printing to the rescue!