When Cody Wilson revealed the world’s first fully 3-D printed gun last year, he showed that the “maker” movement has enabled anyone to create a working, lethal firearm with a click in the privacy of his or her garage. Now he’s moved on to a new form of digital DIY gunsmithing. And this time the results aren’t made of plastic. Wilson’s latest radically libertarian project is a PC-connected milling machine he calls the Ghost Gunner. Like any computer-numerically-controlled (or CNC) mill, the one-foot-cubed black box uses a drill bit mounted on a head that moves in three dimensions to automatically carve digitally-modeled shapes into polymer, wood or aluminum. But this CNC mill, sold by Wilson’s organization known as Defense Distributed for $1,200, is designed to create one object in particular: the component of an AR-15 rifle known as its lower receiver. That simple chunk of metal has become the epicenter of a gun control firestorm. A lower receiver is the body of the gun that connects its stock, barrel, magazine and other parts. As such, it’s also the rifle’s most regulated element. Mill your own lower receiver at home, however, and you can order the rest of the parts from online gun shops, creating a semi-automatic weapon with no serial number, obtained with no background check, no waiting period or other regulatory hurdles. http://www.wired.com/2014/10/cody-wilson-ghost-gunner/
Actually it is a general purpose machine in that it can create anything that is dictated to it by a ".dd" file format and can fit within the volume of the device.
In fact, the process of legally milling a metal lower receiver is easier than it sounds. Using the Ghost Gunner to carve a lower receiver from a raw block of aluminum would be a lengthy, complex process. But the firearm community has long traded in so-called “80 percent lowers,” lower-receiver-shaped metal pieces that sell for as little as $80 and are roughly 80 percent finished—They only need to have a few holes and cavities milled out to become the body of a working gun. The bureau of Alcohol Tobacco and Firearms has defined that 80 percent line as the closest an object can come to a regulated rifle without legally qualifying as one. But precisely finishing the last 20 percent of a lower receiver has still required access to a milling machine that typically costs tens of thousands of dollars....Defense Distributed’s machine can’t carve pieces as large as its competitors, but its small size makes it more rigid and precise, allowing it to cut an aluminum lower receiver from an 80 percent lower in around an hour.
The article is a bit ambiguous on whether the Ghost Gunner could carve from a 0% lower - aka a block of aluminum. It may be that doing so would just take a lot longer. As long as the 80 percenters are legal, you would just buy those. But it is clear that this mill can print more than just lower receivers [ghostgunner.net] from .dd files. It's not clear to me whether the software for it is so specifically tuned to carving 80% lowers, that it would result in legal posturing similar to the State Dept. letter. See the following line:
Ghost Gunner automatically finds and aligns your 80% lower receiver to the machine, with simple installation instructions, point and click software and all required tools.