It's already a thing in orca and prusaslicer at least

I think Roetz 4.0 has done some experiments with this iirc. It worked fine, but it was more like one of those multi-color filaments as there is no way to control the color coming out of the nozzle. He tried with 2 different colors I think, but his setup had 4 wires of filament being pushed through.

There is actually a relative long time between filament being pushed into the nozzle and coming out at the bottom. In between is a reservoir of molted and partially molted plastic, which is essentially a chaotic system. When extruding or retracting the filament, this is actually controlling the pressure inside that reservoir. This makes it extremely hard to get any kind of controlled mix.

You also have the issue of the number of filaments required. Remember CMYK only works when printing on white paper, the white is an important component to the end result. And those don't actually mix those inkts. They just print little dots close enough together for our eyes to lack sufficient resolution and thus see them as one mixed color. For a lighter result less dots are printed, for a darker result more dots are printed and black dots added to go even darker.

So you would need to have 5 filaments being pushed into a single reservoir, which is a challenge. Then you'd never get perfect mixing, even if you machine the combination inside perfectly (look at how nice the machining on Roetz his nozzle was). The pressure inside would vary leading to some filament being pushed less that others, it's a very unstable situation which makes it very hard to perfectly predict or control. And being it's mixing inside that reservoir, there is very little control of how the color comes out. It wouldn't be the same color from all angles due to imperfect mixing and the changing of colors would be a slower gradual thing, not instant. And the way the color presents is also dependent on the direction the nozzle is moving.

The amount of material being pushed in would vary a lot, where we'd want mostly the same continuous pressure on the nozzle side. And when moving reduce that pressure to prevent stringing. Controlling this with 5 filaments would be borderline impossible and would require a high flow large diameter nozzle. So only very large high speed printers would work. Or the filament would need to be thinner, so less material is pushed in, but then you run into compression strength issues in the filament.

I think for practical results, people either just paint it after the fact. Use a multicolor filament for cool colored results. Or use a different technique that offers prints in precise colors.

There is this super cool 3D printing technique from HP that is abandoned now, but does kinda work like you say with CYMK and a white material. It uses inktjet heads to eject a ceramic powder to 3D print. It can make high resolution 3D prints in full color and when baked the ceramic is very hard, so the objects can be practical to use. The big issue with this technology is the powder clogs up the nozzles on the inktjet heads. Just like with printers when the ink dries and the head clogs, it's a nightmare. So those machines need constant cleaning and supervision. When they work they produce amazing results, but the technology is such a pain in the ass, they stopped making the machines. I think they still make the material and heads tho, for people who are already using the machines. I think they are often used in medical settings where they paid a lot for the machine and keep using them.

No idea if if ever took off, but e3d had a hotend that could mix 2 filaments. I've never seen one in person, but messed around with the chimera a bit when it was first launched.

https://www.filastruder.com/...

Binder jet printing is an older 3D printing technology in which adhesive is sprayed on layers of powder to build an object. A mix of ink can be included in the spray to produce detailed color combinations.

https://en.wikipedia.org/...

I feel like I definitellyyy saw a CMYK printer in a VOD of some printing convention a couple years ago? It was presented by some company and looked huge and expensive, wish I could remember who they were.

It's not here yet that I know of. But I feel like it's going to get figured out in a couple of years. I daydream I had was not to blend but to have a filament that would change color with different temperatures.

What I'd love to see even more than that is some kind of pigment cartridge system. You'd use natural, unpigmented filament and the printer would inject pigment in different mixtures as it prints. Just seems... I dunno. More efficient?

I remember seeing a YouTube video (that I might search for and find again if I remember) where some company had developed (and probably patented) an approach that involved inkjet-coloring as it printed. I remember the colors looked pretty pale and washed-out looking. Not vibrant the way I would have hoped. But the approach might be one that could be improved on. 🤷

You would need some mixing chamber. That holds liquid plastic and churns it to achieve the results.

Not to mention having all the filament the same plastic composition.

Injection molds sometimes get stuck plastic in the hearing unit, but it doesn’t mix well and is streaky. Without some staging in a chamber it likely wouldn’t work.

Even with clear filament and dyes, it would taking mixing to incorporate the dyes.

It kinda depends on what your goal is. Is it making a custom filament? or are you thinking of blending colors on the go? And are you looking for commercially available solutions?

If you're looking for commercial solutions, then your guess is as good as mine. I know you can get filament recycling systems, where you crush failed prints and supports before then extruding usable filament. But I think that's not what you're looking for.

Going the tinker route instead, I think it was CNC kitchen that experimented with extruding their own filament by printing spiral of thick filament and then running it through a 1.75mm nozzle. They even got their logo embedded, and it was detectable in the finished prints layers.

But if you're looking to blend on the go then maybe some manual g-code manipulation and custom hotends could work. But given that I asked about experiences with dual input hotend like the one below, and all the answers were along the lines of "don't even bother", I guess that you having to do a triple or quad input hotend won't make it more likely to succeed.