Install a 3D printer in your house and it could pay for itself in just four months, a group of university engineers have claimed.
This is according the Michigan Tech "Open Sustainability Technology Group" (also home to "3D Printers for Peace"). Dr Joshua Pearce and his acolytes say that anyone who uses an open source "self-replicating rapid prototyper" ("RepRap": it can't replicate itself, though it can make some of its parts) to manufacture just 20 common household bits and bobs would save themselves between $300 and $2000. Assuming that a normal household needs 20 such plastic things a year, and that you assemble it yourself, the printer would pay for itself after a time span between 4 months and 2 years.
The twenty useful items chosen as examples include two iPhone "docks" - naturally these don't include any cables, plugs or connectors, they are really just bits of plastic - an iPhone case, an iPhone tripod, an iPad stand and a wrist holder for an iPod Nano ("still a work in progress", according to its designer). All have the rough-hewn/shoddy look characteristic of things made in affordable 3D printers, and don't really set off the expensive shinies they're meant to hold, but perhaps an enthusiast might tolerate them. Realistically you can't buy equivalents as nobody sells products as low-quality as this, but the zealots of the Open Sustainability Technology Group consider that you would spend at least $70 and perhaps as much as $250 if you bought a similar number of normal pieces of plastic in which to cradle your iThings.
There are also various other kinds of startlingly ugly tat - necklace organisers, car-key organisers, a kitchen spoon rest*. Then there are also other things which you can print bits for, but which require metal parts and fasteners as well, such as an old-style safety razor and a kitchen paper-towel holder. All these things could be made from wood (or plastic, come to that) by anyone possessed of simple tools and basic skills, but apparently they're much better home-made in a 3D printer even if the finish isn't as nice.
About the only really credible suggestion was that you might 3D-print some shower-curtain rings instead of buying new ones: or maybe even a new shower head, though the designer in that case admits that pressurised water and 3D-printed components don't mix well - also that you'll have to spend some time poking out the holes with a hot needle or similar (or even - gasp - use a drill?)
Far the biggest chunk, fully $100 to $800, of the suggested possible savings comes with the idea that one needs custom orthotics (shoe inserts for people with foot problems) and that one already has an accurate 3D design suited to one's own feet - perhaps obtained by somehow getting a set for free and then scanning them in a 3D laser scanner, again for free.
The report's authors claimed that the savings offered by RepRaps means that 3D printers are a smart purchase right now. Although do remember to print out that set of spare parts before it breaks down.
As both upgrades and the components that are most likely to wear out in the RepRap can be printed, and thus the lifetime of the distributing manufacturing can be substantially increased, the unavoidable conclusion from this study is that the RepRap is an economically attractive investment for the average US household already.
A RepRap is available for about $575 if you're willing to spend 24 hours assembling it yourself, or between $799 and $2199 for commercially manufactured models.
We particularly noted the bit about how you could save a fortune by 3D-printing yourself a "safety razor" handle/holder unit and using disposable double edged metal blades in old-school style instead of disposable razors or disposable plastic heads:
Consider the case of shaving. Most American men who shave buy disposable razors or disposable razor cartridges that fit into reusable handles because the initial cost is much lower than more robust product options (e.g. a safety razor, for example, costs US$20–80 online). This initial startup cost prevents consumers from using the more economical (over the life cycle) choice. Now that there is an open-source safety razor design available for free download (thing: 43,568), which costs about 36 US cents to print, the barrier to entry has been eliminated for everyone with a 3-D printer. A 10 pack of double edge safety-razor blades cost about US$5 (28 cents per blade) on Amazon. If it is assumed that an average user consumes one double blade every 2 weeks the blade costs for open-source safety razor shaving is about US$7/year. To put this in perspective, the cost of shaving using drugstore blades or cartridges is between US$100 and US$300/year  and . Assuming the average man shaves for about 65 years, using the printed razor and only replacing the metal blades would result in a net savings of between US$6500 and US$19,000 over a lifetime.
Or you could just buy a proper oldstyle safety razor for a few dollars/pounds and enjoy exactly the same savings, and skip out buying the 3D printer. Though many would say there are reasons why people largely stopped using such razors: twin blades do shave you better (even if three or four is probably overkill) and many people can't be bothered fiddling about changing blades and possibly cutting themselves in the process. Maybe there are a few who are offended at throwing away a comparatively large amount of good steel every time, too, as opposed to a couple of edges and some plastic.
We won't even get into all the stuff about the coming future of 3D-printing cottage industries, the plunge in consumer spending and all the rest of it. It's amazing stuff, and not a bit like what they were teaching engineering students when one of your correspondents was at university. The study can be read here in the journal Mechatronics - but why ever would you pay for it when you can read it Open Sustainability style here. ®
*A Vulture Central straw poll found that most have only ever seen such a thing in American diners, though one staff member's mum uses one to keep slices of lemon in and another's wife actually does rest messy cooking spoons on hers - apparently preferring to both wipe the counter and put something extra in the dishwasher afterwards.