I think it's time for an open source 2d printer project, we have open source 3d printers and the technology is much more complex than 2d. Time to put HP to sleep
I think it is a combination of the required precision, liquid ink vs solid filament and the difficulty of handing paper vs simply moving a print bed on a 3d printer.
I'd argue that this is not an issue from a technical perspective, which would halt open hardware endeavours.
The precision is mainly a problem regarding the used motors / actuation system, which in turn is "just" a money issue, but the hardware is there. Paper handling is pretty easy.
I don't know how complicated it would be to create ink or laser cartridges, but given that there are a lot of 3rd party vendors who offer refill services, I suppose it is manageable.
My guess for the reason why there is no open hardware 2D printer yet is, because nobody has seriously started such a project yet.
There was simply no need, we already have great 2D printers. Like Brother, which doesn't have DRM, doesn't need internet, and doesn't complain about anything ever.
The hardware precision is the hard part, along with speed. Most hardware parts wouldn't be hard to get because most of the printer is just motors, rollers, etc, but the print head itself is the part that would be the hard part.
Here's a good reference, from that website describing thermal bubble which is the more common technology;
Thermal bubble - Used by manufacturers such as Canon and Hewlett Packard, this method is commonly referred to as bubble jet. In a thermal inkjet printer, tiny resistors create heat, and this heat vaporizes ink to create a bubble. As the bubble expands, some of the ink is pushed out of a nozzle onto the paper. When the bubble "pops" (collapses), a vacuum is created. This pulls more ink into the print head from the cartridge. A typical bubble jet print head has 300 or 600 tiny nozzles, and all of them can fire a droplet simultaneously. Click the button to see how a thermal bubble inkjet printer works.
So that's the part that would be hard to manufacture, and even if you were able to do it and open source it, it would likely be slower and less precise than the other big companies.
I'm not an engineer, but I work tech support for one of the inkjet printer companies and we learned how the printers work. It's pretty interesting, and there's more to consider than you might think. Like color accuracy, if you want to make green on paper then you use cyan and yellow ink. Not only do you have to worry about making sure the print head spits out the correct ratio of cyan to yellow, you have to worry about which color it deposits first. If it drops yellow first, that's going to be a slightly different hue than if it deposits cyan first. So how do you make sure it deposits the correct color when the print head is moving left to right and back to left? If it deposited ink on the return back to the left, it would be dropping the opposite color first so your colors would be slightly different leading to visible bands or lines. And having the print head return to the left side without printing would take twice as long to print. You have to design the print head with that in mind, and more.
Anyways, I'm sure it's possible but it would take a lot of time and effort to make sure it worked well enough to be comparable to the big names with proprietary tech.
For 3D printing to work, you basically just need some standard motors to move a thing that gets hot around. Yes it needs to be pretty precise, but it's only printing at a single point that moves. Classic 2D printing not only prints across the whole sheet at once, it is also sometimes expected to do it in color (which does take multiple passes usually). As for the technological aspects of conventional printers, I really don't consider myself an expert, there are great videos online. However by my understanding, a laser is often used to trace the exact contents of the page so that the depositing material is picked up and placed. That sort of light manipulation is already more complicated than everything most 3D printers do.
Basically, you could build a new 3D printer in your garage using off the shelf parts and some knowhow, but good luck even repairing a 2D printer with a serious problem in its printing mechanism, though this difficulty is certainly not made better by companies such as HP
As it stands now printhead technology for quality prints needs microscopic precision and materials like precisely perforated foils that are just not easy to make outside of a specialized fabrication shop, and even then it won't scale.
For example, a very important patent for any inkjet is the one where heads self clean, basically maintenance. Without that, an inkjet printer would be a pain to have.
I'm sure there would be workaounds to that, also I'm not selling anything, just sharing a project and list of components. i'm not a lawyer but i'm pretty sure there's nothing they can do to stop me