Bad engineering journalism: reporting on “3-d printing of guns”

Everyone and his brother is reposting one of the many articles on the guy who used a 3-d printer to build an AR-15 lower receiver. They’re making it seem like this is important, because pretty soon you will be able to use a rep-rap to print up an AR-15. This isn’t stats-jackassery, but it is the most pig-ignorant engineering jackassery I’ve seen in some time.

The Wired article  isn’t bad, and it doesn’t tell any obvious lies beyond the title and Brady center nonsense, but it leaves you with the impression that 3-d printed assault rifles are just around the corner. No, this is not possible. This will never be possible with 3-d printing technology; not now, not any permutation of it in the future. The guy who did this trick said as much himself; the media frenzy over this is ridiculous. He’s performing a silly engineering trick, not pushing technology forward. Some of the other stuff written about this demonstrated criminal neglect of fact. There should be a professional penalty for journalism as bad as displayed in the Business Insider article, beyond my calling the author out as a gibbering ignoramus, but alas, there is no other penalty for telling hysterical lies in public.

The AR is one of the few rifle designs where you could even think about using a lower receiver made out of plastic. It is also one of the few rifle designs where the lower receiver is legally considered “the gun” by the ATF. In other nations (like, I think, Canada), the upper receiver of the AR-15 is legally the gun, and a plastic version would melt if it didn’t dissolve from mechanical stress the first time you fired it. Sane people build their AR lower receivers out of aluminum or steel (there are a few composite ones on the market using advanced lightweight materials). Less sane people whittle them out of pieces of wood, just to show that it can be done.  Since the creator of this object isn’t suicidal, he’s not even using the .223 Remington ammo typically used in AR-15 style guns; he’s using .22 Rimfire, which is ammo with about 1/10 of the already relatively low muzzle energy of .223 Remington. Virtually all of the important parts of this project are manufactured from metal by professional gun makers, and they always will be.

Here’s a picture of the AR lower receiver he’s printed:

The first thing you’ll notice; this is not a solid object. It’s a bunch of thin layers of plastic more or less stuck together. This is something you  always notice when you handle solid printer output, but particularly the egregiously bad output of home solid printers. It’s badly made; barely a solid at all.  The second thing you should notice is the little red arrows, pointing towards the crack when he tried to drive a necessary pin through the thing. It disintegrated along a predictable fault line like the piece of layered plastic junk it is. He fixed it using glue. FWIIW, you could build a lower receiver out of epoxy using hand tools, and it would be a lot stronger. It would still be a dangerous piece of junk, it would be significantly less dangerous to the operator than this contraption, because set epoxy is an actual solid.

Another picture:

Oh look, a shiny piece of aluminum. One which he machined on his lathe. Screwed into the “receiver.” This is necessary, because the plastic isn’t enough to protect the user in case the locking mechanism fails. He also needed to machine his plastic receiver once it was printed, with hand files, drills and some extra bits of glue to hold it together. Hardly a print and play operation here. If he just wanted to make a working gun out of a barrel and bolt, he could have done so with duct tape, modeling clay and superglue.

Note also, that you could build most parts for virtually any kind of gun if you have a $200 lathe (and some tooling) in your house, which this guy already has. It would probably be less trouble than this project, and it would certainly be safer for the operator. Some kinds of submachine guns can be made out of muffler tube and a hacksaw if you have the barrel and trigger group. The British invented their Sten gun to be this way, so the resistance in occupied Europe could hose the Nazis down with hot lead. Guns are easy to make. There are cottage industries for doing so with hand tools in the wild places of the world.

As I noted above; he could have done this using plastic or even bits of pine wood, and it would work better. People have; check the links. Why don’t people freak out over that?

I think the reason people freak out over this is the  unreasonable enthusiasm for solid printers. I’ve used the output of early high-end solid printers, all of which are far superior to hobbyist garbage like the “rep-rap.” They’re useful for making plastic parts for prototyping purposes. A firm I worked for in 2000 used this tech to make a dummy iphone (which hadn’t been invented yet: we were ahead of the curve) to mount accelerometers to. That’s the kind of thing solid printers are useful for. The hobbyist hysteria over 3-d printers is unwarranted.  Serious people who want to make useful objects, like, I dunno, the humble screw, will make them out of metal using machine tools and casting, and maybe use a solid printer for difficult to machine plastic parts. Difficult to machine plastic parts are pretty optional when constructing useful devices; usually the solid printed part ends up being something like a plastic box (which is effectively what this lower receiver is; a box with some holes in it). In ye olden days, the box would be made out of wood, which is stronger and looks better, and can be made without some dope fiddling on a computer.

Nerds have this fantasy that solid printers will make them infinite open-source useful objects in … the future. This is the sheerest fantasy; a fantasy that can only be held by people who have never made a useful  mechanical object in the workshop. Solid printers can make crude unassembled plastic parts; nothing else. No electronics can be made in this way. No assembled parts can be made in this way. Even if a home printer could print things of metal (this will never happen on a cheap home use basis as you need a very high power laser to melt metal powders), it will effectively be sintered metal, or sintered plastic-metal composites. That’s not the same thing as a machined piece of solid metal. It doesn’t have the same mechanical properties, and barring some preposterous breakthrough, it never will. Some parts will not ever be realizable with this sort of technology: for things like, say, a plastic simulacrum of a rifle barrel within linear tolerances, you’ll always need specialized machine tools. Not that machine tools are terribly difficult to obtain or use. Hobbyist CNC (aka computer controlled machining) tools have been around for decades, and they’ve hardly amounted to “home printing of useful objects.”  The CAD design for this plastic lower comes from a CNC design which has been freely available online for at least 10 years now. Since solid printer nerd enthusiasm outnumbers CNC nerd enthusiasm by many orders of magnitude, nobody made a fuss over that. Anyone who thinks solid-printing is awesome should get on a lathe and figure out how real objects are made before they yap about rep-rap. It’s fun. I learned how to do it as an undergraduate, and keep an Austrian clockmaker’s lathe in my kitchen for when the mood strikes.

The guy who did this should be applauded for his engineering cleverness and brass testicularity in attempting to fire such a dangerous-to-the-user object. The doltish journalists who wrote breathless articles about  it should mocked for their hoplophobia and ludicrous ignorance of the most rudimentary engineering knowledge.