I might have been too negative, but only by a hair. FDM printers do have their uses, but it's a very niche technology that is difficult and time-consuming to learn. Lots of really cheap and easy fabrication methods are almost totally ignored by the maker community, while 3D printing is put forward as the glimmering future of manufacturing.

Your story is very positive, but it falls a long way short of justifying the purchase of an expensive machine and the investment of many days of effort in learning how to use it. How many people have a burning need to produce hundreds of dollars worth of spare parts for toys?

>the materials science is an obstacle made of tissue paper- as in, we're already blowing through it handily. I don't know what you're printing with

I've seen test results from the absolute best case scenario - professionally designed parts printed on a $200k Stratasys machine using ULTEM 1010. The material properties just about match injection molded ABS. Parts made on consumer machines using ABS or PLA filament are generally an order of magnitude worse.

If you tailor the use-case to one a consumer 3D printer can't match, then you can certainly show that the materials science won't allow the consumer-grade machine to compete- the issue here is one of imagination and applicability. Like the other fellow here says, what you're saying has deep shades of the same "why would I even WANT a computer, green monochrome, blocky text, stupid games?" Arguments I had the misfortune to deal with personally, and the good fortune to avoid being swayed by. It's very much still a hobbyist's game, and just as it was then, when it would be substantially less time-consuming for most hobbyists to just, I dunno, modify their spreadsheets by hand and do calculations with a slide-rule than to program a computer to modify the order some little blinking lights came on.

So powerfully, we don't really disagree- I concur that my use case (replacement parts for toy robots) doesn't justify even a 500$ 3D printer- but the communal one we share at university was extremely valuable (did I mention the quotes from services like Shapeways for the part were in the 17-25 dollar range, where I was charged 3-4 bucks?). Moreso, the REAL value here is in all the crazy designs I've been concocting since then, like the adjustable desk I've been toying with building for ages, but always found my toolbox, workspace, and expertise somewhat short to make the gear setup- the portion of the project that intimidated me would be trivial and cheap with this 3D printer- and this printer, it's one of the ones that really sucks! This breaks that barrier right down, and that's all technology is really for, anyway- to help us make our visions into realities.

You obviously know more about materials than I do, but I think that your perspective is skewed by upper limits- you're trying to decide this technology by comparing it to other tech that it has zero need and zero business trying to compete with- when we DIY guys require materials that strong, then maybe we can talk (not saying it wouldn't be nice, and break down more barriers, I'm saying that it sounds like you're saying that unless it can compete with injection molded ABS plastic, it's not worthwhile, and I hotly contested that assertion), until then, you're trying to shortchange our moon rockets because they won't get us to Mars, and that's pretty silly, in my book, even if it's true.

So, indeed, hobbyists machine- someone purchasing this as an appliance like a refrigerator- meant for convenience and time-savings, I can agree that they'll be disappointed. In the meantime, hobbyists who only want to give the vision-to-reality ratio a boost are going to continue to be tickled pink at their 3D printers, and I suspect that their enthusiasm will drive enough interest and investment in the technology to maybe deliver some of those high-quality, cheap Laser sinterers you mentioned before- all possible as long as there's an enthusiast market to consume the hobbyist level iterations along the way! :D

I'm thinking if I want to spend a bit of money on a computer-controlled making gadget I'd probably do better with a laser cutter. That covers a lot of cases (e.g. a gear should be just as easy on one of those as with a 3D printer, right?), and my impression is that the people I know with those tend to make more useful things than those with 3D printers, largely because of the material flexibility. Am I missing something?

Very much so. At my local hack space there's a week long waiting list to use the laser cutter, while the 3D printer gathers dust.

Nice, did you put the 3d model of the gear on Thingiverse? To me, the access to a large database of useful 3d objects that you can print easily is another huge advantage of 3d printers.

<mumbles something nearly unintelligible about having started modeling it himself, but then having checked Thingiverse, he got it off of Thingiverse because someone had already done a fantastic job of modelling the piece. :D >