zlacker

>>pangor+(OP)
Printers are cheap and widely available, which leaves a DIY printer which is going to be slower, more error-prone and more expensive as a very niche idea. There is a clear benefit to buying or building an open hobby 3D printer, whereas that's harder to argue for a 2D one - while there is a lot of crap around, there's enough workable choices, aftermarket inks/toner works, you likely won't be modifying/tuning a 2D printer the same way you maybe would with a 3D printer, ...

Ink delivery is likely the main challenge (although I've seen some low-res attempts), combined with the speed and precision needed for a good printer - reaching a few hundred DPI requires positioning things quite precisely. Laser printers are interesting, but then you need specialized parts like the drum that I'd expect to be difficult to produce in single quantities.

Open pen plotters are a thing, but again not typically used for normal printing duties.

>>detaro+a2
I don't think this is quite right. An open source 2d printer would allow for a lot of things commercial printers don't allow for. For example, I'd like to be able to print on things which are not paper. If I had an inkjet head mounted on something, there's a ton I could do with it, from modifying it to print directly on fabric, to integrating it with other fabrication technologies to make decorated objects. Even a CNC mill or laser cutter with an integrated printhead would be invaluable, both for labeling parts and decoratively (for making pretty parts).

There's a massive growth curve too. If we could find a way to print on plastic, we could integrate this with a 3d printer and make decorated parts. I think this would be multiple stages of amateur R&D, but it would eventually happen (yes, I suspect someone will respond with all the technical issues why it can't work with current technology, ignoring all disclaimers -- I am aware this won't work right now).

I think of tons of other use cases.

I think the problem is as others have described. Making a printhead costs peanuts, but engineering one and NREs are astronomical. Ditto for paper handling, and many other parts of the printer. There used to be an printhead open enough for DIY (you could buy them in quantities of 1, and there was a spec sheet), but it's not sold anymore.