3d printing isn't, in many cases, any better than CNC machining (which has been around since the 1950's).
CNC machining can give a better finished product, since you can make things out of high carbon steel instead of powdered metals (or plastic).
The skills required for programming CNC and modeling for 3d printing are about the same, and the cost isn't terribly different between 3 axis CNC and 3d printing, while CNC is about a hundred times faster.
What is the difference to the customer between carving something out, and building something up?
Hollow 3d printed steel components for cars would be cool, but ultimately you'll have to machine some of the surfaces.
I admit, you can make cool plastic balls with smaller balls inside them, which can't easily be done with CNC, but really, what is the big deal?
To me, it feels like evolution, not revolution.
Author of Shades of Thomas Paine, a common sense blog with a Libertarian slant.
Also author of Stick it to the Man!