The ambition of the RepRap project (“replicating rapid-prototyper”) is undeniably cool: to design a machine which is essentially a self-replicating 3D printer. By building up objects layer by layer, rapid prototyping technology can be used to manufacture the parts for just about any simple object or machine. It would be like having your own little factory in exactly the same way that having a laser printer is like having your own printing press, except that you can use this little factory to make another factory to give to your friend.

Theoretically, desktop manufacturing technology then spreads exponentially, until everyone can make whatever material objects they need from downloaded plans, for only the cost of feed plastic.

The dream is best explained in this excellent little video:

It’s hard to overstate the fundamental shift that would come with truly widespread desktop manufacturing. Right now all of the objects we use are manufactured somewhere far away and shipped to us, and the designs are expensive and slow to  change. Instead, imagine if everyone had a household appliance, perhaps fed by spools of plastic and metal wire, that could manufacture just about any object from plans downloaded from the internet. It’s hard to see how private designs could compete with millions of amateur object designers geeking out over their widgets for the benefit of humanity, which means that designs for all the basic desirable objects would be freely available.

Want a new phone? Download the latest Android phone plan from the Open Handset Foundation. That’s cool, but the really cool thing is this: everyone in the world could have one for the price of plastic. More to the point, everyone in the world could have e.g. irrigation pumps, car parts, light switches, medical devices, essentially all the trappings of modern technology.

It is of course debatable whether or not an increase in humanity’s use of energy-consuming technology is a good idea at this time. However, it seems to me unconscionable to deny it to the world’s poor just because we got there first. Further, one could also replicate the parts for home biomass reactors, electric cars, and other advanced energy devices — regardless of whether or not anyone can make a profit selling such items commercially.

New versions of the replicator with enhanced production capabilities (now with integrated circuits!) would be designed to be manufacturable using existing models. This means that manufacturing technology would itself spread virally. To bootstrap this, all you need are a few basic self-replicating machines, then the technology passes from friend to friend until the whole world is saturated and capable of producing all future upgrades.

But we are nowhere near that dream. There’s a lot of promise to desktop manufacturing, but I’ve come to believe that the RepRap approach is probably not the right one. And I’m going to try to explain why.

Back to reality. Today the RepRap team has succeeded in designing and building a cheap 3D printer which prints in plastic only and can produce about 50% of  its own parts. This is a historic event, and should not be underestimated. However, producing a new machine still requires a lot of basic hardware such as metal rods and screws, and also more exotic components such as specific integrated circuits and stepper motors. In RepRap’s evolutionary analogy, these raw parts (as well as plastic filament feedstock) are the naturally produced “vitamins” that the RepRap consumes from its environment in order to reproduce. As time goes on, the team hopes to produce designs for upgraded RepRap machines that can manufacture more of their own parts, and not incidentally the parts for more complex objects too. For example, they hope to be able to deposit metal films with the next generation machine, which would allow the RepRap to produce electrical wiring and basic circuits.

All very lovely, but it’s time to examine the reality of this technology. Today we have a prototype design, and a vibrant community of people experimenting with and working on self-replicating desktop manufacturing. Good. But we are not by any means on the threshold of a viral explosion of manufacturing capability, because the machines are not self-replicating exponentially as hoped. A very insightful post from a site called The Clanking Replicator explains the situation:

By the second quarter of 2008 Vik Olliver had managed to print a full parts set for a Darwin with his own Darwin machine. Then a very curious and totally unexpected thing happened. Fully 6 months went by before a Darwin replicated again, this time in Canada. By that time, however, by Dr. Bowyer’s estimate of the population of Darwins was in the low thousands. What had happened?

Basically, Darwin morphed into a fully industrial product. It began with the controller boards being outsourced for production by the Reprap foundation and has culminated with a shippable kit purchasable for US$1,100  requiring little more than the sort of assembly you’d be expected to apply to something bought from Ikea. What is getting built out there in its thousands, to use Dr. Bowyer’s metaphor, is 100% vitamins – 0% replicated parts.

The initial self-replicating manufacturing machine, code named Darwin, has so far completely failed to spread virally. People are building this prototype device, but not by using another 3D printer. I want to examine why, and what this means for the future of desktop manufacturing.

First of all, the machine is far from “self replicating” from the user’s point of view. What you get when the existing design “replicates” is a set of plastic parts for a new machine. To this must be added metal hardware, integrated circuits and electronics, and stepper motors. Then the whole must be assembled by someone already skilled in making machines (here I must disagree with the Clanking Replicator post to say that assembling a RepRap still seems to me quite a complex undertaking, the sort of thing you wouldn’t want to attempt without jeweler’s screwdrivers and a multimeter.) This is hardly a consumer item. To press the evolutionary analogy, its niche is limited to hardcore geeks. This might still allow exponential growth to saturation of that niche, but desktop manufacturing is not going to transform the world until it goes solidly mainstream.

This means a consumer product. The RepRep must be no harder to reproduce and assemble than Ikea furniture; if the directions are longer than a page, you’re going to lose 95% of your market immediately. Further, the parts that cannot be desktop manufactured must be ridiculously common. You need to be able to get them at the hardware store, even in places where hardware stores are very limited (especially in such places, if we’re seriously going to consider transforming Africa.) Stepper motors are far too difficult to obtain, even in developed countries.

The RepRap team recognizes this, and is trying hard to make the machine simpler to obtain in at least two ways. First, the second generation system promises to be simpler, with fewer parts, a more robust mechanical design, and easier assembly. Second, they are looking into ways to expand the types of parts that the RepRap can print. Metal film deposition is an obvious way to go, because then the RepRap could print its own wiring and circuit boards. With time, the team hopes to further simplify the replication process.

Except, why not just buy the parts as a kit? Or even fully assembled as an industrial product? Although the exponential replication story is a beautiful solution to the problem of distributing desktop manufacturing technology, do we really care? Modern civilization is already extremely good at getting an object into the hands of absolutely everyone, everywhere. The towns ringing the Sahara desert may not have electricity, but they sure as hell have Coca-Cola, and usually motorcycles too. No one not a geek is going to care about trying to self-replicate a machine until that process is easier (and cheaper) than buying a finished model at Wal-Mart.

Which brings us to the second major problem I see with the RepRap concept: none of it matters at all until the thing is actually useful. This means making thing that people want other than parts for more RepRaps. Under the heading What Can It Make? the RepRap website shows us a fly swatter, a pair of child’s plastic sandals, a coat hook, an iPhone-to-dashboard mounting bracket, a strainer, a plastic ring, various brackets, a couple of gears, and a crappy martini glass. I understand that this is first generation technology, and it is very cool to make this stuff at home, but is there really any non-geek demand for a machine that can make these sorts of objects?

In my opinion, the RepRap community has so far focussed far too much on the coolness of a self-replicator, and not nearly enough on what it could be good for. For a research project, this is fine. However, the RepRap will never achieve viral status among the general public unless it’s actually useful to people who don’t care about technology. Which, for the purposes of this discussion, is everyone.

Now, 3D printers are just the thing for low-volume runs and prototypes, which is why such machines have traditionally fallen under the category of  “rapid prototyping.” It’s a great technology, and I am very glad to see someone attempting to bring the price down. But it will not be a widely adopted consumer technology until it’s a better way to get stuff than going to the store or ordering it online. This means designing lots of useful things that are cheaper or easier to manufacture on the desktop than they are to obtain through the usual channels. Unfortunately, those places where consumer object distribution is most limited (it’s hard to get a martini glass in the Sahara) are exactly those places where it would be hardest to get parts for a home-built desktop manufacturing machine. Put bluntly, the RepRap team does not yet have a product that someone wants.

I have in mind a detailed analysis of common consumer items and their availability. Small plastic widgets are manufactured by the millions in China, and so are of interest only if specialized and currently difficult to obtain. But this is the market niche that high-end rapid prototyping machines already occupy, so no go. We won’t be desktop-manufacturing plastic spoons any time soon. More promising are assemblies of several parts, such as toys and small machines. Maybe spoons aren’t interesting, but I wonder if an entire suite of kitchen utensils on demand would be, including egg beater blades and corkscrews, or an entire set of model cars lovingly 3D modeled by online enthusiasts. After that, we rapidly get into objects that a RepRap cannot hope to produce. No one will be manufacturing their own light bulbs or microwaves any time soon.

Except that asking about the manufacture of existing objects is a little deceptive. Current consumer goods have been designed to optimize the cost per unit when thousands or millions are produced in a single factory. Desktop manufacturing imposes a different economics: the relevant parameters are raw materials cost, printing time, manual assembly time, and of course the requirement for parts that cannot be fabricated on the current generation of printers. An analysis of what could be made on the desktop must also be an analysis of how existing classes of objects could be redesigned to be amenable to desktop manufacturing. It’s not just about building a printer, but about redesigning the entire manufacturing supply chain and inventing entirely new fabrication methods. Want to reduce the external parts count? Perhaps new types of printable plastic fasteners can replace screws. Is the thing too complex for the user to assemble after printing? Integrated monocoque designs might be the answer. As far as I know, no one has yet tried to design a monocoque toaster.

This sort of research will also answer questions about what capabilities are most sorely missing in the current generation of printers. The ability to fabricate electronics is obviously desirable, and metal film deposition seems like a good first step. But is it really? The key criterion when evaluating any new capability must be how many useful objects could be fabricated. Asking what fraction of the parts in a RepRap could be made by a RepRap is only interesting when desktop manufacturing technology starts to become competitive with standard manufacturing techniques for complex electro-mechanical objects.

Which brings us to cost. I love the idea of downloading the design for whatever I want, but I still don’t think I’m going to print the vast majority of things I need. For plastic spoons, an injection moulding machine plus international shipping is going to be cheaper than desktop manufacturing for a long, long time. This gives desktop manufacturing a potential advantage for complex objects or short runs, especially if the labor of assembly can be avoided by automated production. Unfortunately, complex objects and minimal manual assembly are precisely what current desktop manufacturing technology is worst at. I can imagine a very advanced machine that can make its own integrated circuits and assemble them too, perhaps with its own little robot arm that is controlled by the downloaded manufacturing program. Awesome, and one day potentially a cheaper way to get one’s hands on that hot new laptop design, but that capability is a very long way away. Instead, the desktop manufacturing research program needs to ask itself what sorts of objects are not only useful and possible in the near term, but expensive to manufacture or distribute by conventional techniques. As an analogy, anyone can now print a book on their laser printer, yet we still buy bulk-printed books.

Finally, it seems to me that the RepRap team is trying to solve two problems at once, and is unclear about their separation:

1. Developing a useful desktop manufacturing capability
2. Getting that capability into the hands of everyone

The self-replicating exponential growth ecological analogy is a beautiful conceptual solution to #2, and it is also a useful technological driver for #1 because a 3d printer is a pretty complex thing to print. The RepRap team is also proud to be distributed, open-source, etc. and this is an admirable approach to #1.  However, these are far from the only solutions to these two problems.

Starting with the distribution problem, a moment’s thought reveals that it’s already extremely well solved! Getting a physical object to whoever wants it wherever they are is all but trivial at this point in history. We do already this with everything from soft drinks to mobile phones (and believe me, everybody has both.) The problem is not getting the object to people, it’s making it as cheap as possible to do so. This means that driving down the cost of desktop manufacture is the key goal; self-replication is only interesting if it’s cheaper than assembling it in China and shipping it.

As for the technology development problem, there are lots of approaches other than distributed and open source. Many basic technologies have come out of government research programs (such as jet engines and the internet) and private enterprise is of course reknowned for efficiently producing and distributing innovation. So rather than distributed global self-replication, how about this plan: figure out a way that someone can make money off of the idea, at least for a little while. Do the research discussed above and write a business plan. Take the core RepRap team and add to them the best mechanical engineers, manufacturing specialists, and consumer product designers that the world has to offer. Take the plan and the team to your favorite venture capital firm, and ask for a few hundred million dollars. I’m willing to bet that a well-funded team of crack personnel could solve the daunting technical problems of useful desktop replication much faster than the current distributed organization, and the debt to the VC would provide a strong incentive to build something that people actually wanted. This doesn’t immediately imply monopoly: open-source the design if you like, and make money off being the first to get there. There is no shortage of potential ethical business plans.

If the goal is to develop desktop replication technology to a useful state and get it into the hands of as many people as possible as quickly as possible, then I am not at all sure that self-replication is a useful near-term design goal. I do love the idea, and I believe that, eventually, self-replication will become a useful manufacturing strategy. I also really like the upgrade bootstrapping concept, where each new generation of manufacturing machine is designed to be fabricated on the last. This is an approach that will allow advances in manufacturing technology to spread at the speed of information. But we’re not there yet. Those working on desktop manufacturing technology today will need to concentrate on cost and usefulness, probably for many years to come.