[MayeulC]

Hmm, I am not in the 3D printer space anymore, but I am surprised they went with alternating layer per layer, as that severely limits resolution. It's probably the simplest way to achieve reproducible results, but I can think of a few other ways:

* the simplest is just mixing filaments, like one mixes paint. The article doesn't spell out the reason it doesn't work, I am curious as to why.

* together with alternating layers, colors could be alternated in the same layer. Some purging may be necessary, but I think you could either: accept some mixing (compute its impact to compensate) / take into account the volume in the nozzle (extrusion "latency") / discard the unwanted part in the infill (at the cost of less smooth edges)

Of course, the hard work with any approach, including their current work, is calibration, as the article highlights. I wonder if off-the-shelf monitor calibration sensors could help with measuring the filament you have at hand.

[imtringued]

>the simplest is just mixing filaments, like one mixes paint. The article doesn't spell out the reason it doesn't work, I am curious as to why.

This requires you to control both filaments independently directly at the extruder. Dual direct drive for a single nozzle sounds like an engineering nightmare. The extruder head is going to be huge.

There is also the obvious problem of how to stirr the filament. Printing temperatures aren't hot enough to turn the plastic liquid, they just make it soft enough to drip out the nozzle. This means you can't just feed the filaments at continuos rates, you will have to use a PWM scheme where you extrude the first filament and then the second filament in extremely small discrete increments. That switching will give you the necessary agitation without building a throwaway nozzle that can't be cleaned after a clog.

All of this sounds like it would take at least a year for a well equipped research department to figure out. It's definitely not the simplest solution.

EDIT: https://www.reddit.com/r/ender3v2/comments/ssuw3i/my_crazy_p...

Just the hot end of this extruder costs $70 alone. This is definitely not going to be cheap to do.

[wongarsu]

Minuteman on youtube has a four extruder single nozzle setup for speed printing. He occasionally uses multiple colors, and they basically don't mix in the nozzle. The cross section of an extrusion looks like a pie chart

You would need special nozzle geometry that encourages mixing, and likely much higher temperatures. And any such mixing geometry will trap some filament. Switching from dark to light colors might require purging with meters of light filament to get all traces of black filament out

[MBCook]

Imagine trying to clean that out if it jams.

[MayeulC]

Thank you for the detailed answer. This is an interesting engineering problem.

I wish I had more free time, a gearbox or a 4-way differential can probably be used on the extruder head to control the mixing ratios.

Regarding the necessary research, I can picture it being cracked either by hobbyists, or industrial-scale (patent-heavy) players. I imagine that consumer-facing players such as Prusa do not have the means to heavily invest in R&D.

[gamblor956]

the simplest is just mixing filaments, like one mixes paint.

That is actually the hardest way to do it, because that's not at all how 3d printing works. 3d printers take strands of plastic (aka "filament"), soften them up to being melty but not melted, and then "extrude" them, like cake frosting onto a surface. As with cake frosting, in order to mix colors, you have to do so before the extrusion step, so you would have to make your own (filament), and the machinery to do so is not cheap.

The thing about first order thinking is that it is very rarely useful, because the actual experts in the field have almost certainly thought of all the things that first order thinkers come up with, and deemed those ideas unworkable for various reasons.

[MayeulC]

Hence why I was asking the question, thank you for answering, I did not consider the high viscosity of the filament when I wrote this. As you say, it can be worked around, but that would require extra complexity/cost.

[kayson]

I wonder if you would get good enough results by just extruding two separate filaments simultaneously. Sure, they won't fully mix, but with thin enough layers, you'd benefit from the same visual processing that makes alternating layers look like a solid color...

[jononor]

Dual color filaments exist, and they do not mix at all... It gives the objects a nice transition when rotated. But indicates that color mixing in the nozzle is probably pretty difficult?

[zahlman]

> The thing about first order thinking is that it is very rarely useful, because the actual experts in the field have almost certainly thought of all the things that first order thinkers come up with, and deemed those ideas unworkable for various reasons.

Sure, but a useful article would focus on explaining the consideration and rejection of those obvious ideas, and what actually had to be done to implement something similar — rather than focusing on the even-more-obvious background material (how 2d printers have worked for decades) motivating the obvious ideas.

[gamblor956]

That is a very different article from the linked post, which was about introducing the cool new tool someone else developed into their own program.

If you want a discussion about the other ideas and why this specific method was chosen, go to the original tool where the creator discusses those things.

[naasking]

> the simplest is just mixing filaments, like one mixes paint. The article doesn't spell out the reason it doesn't work, I am curious as to why.

Plastic flow is laminar, where colour mixing requires turbulence. If you make a turbulent nozzle, it's basically impossible to print reliably with it (the pressure used to push filament out of the nozzle is mostly absorbed/redirect into turbulence).

[MayeulC]

Thank you for the clear & concise answer. A rotating nozzle and/or alternating colors might work then, but that would be a relatively complex engineering project.

[circuit10]

This is a software solution designed to work with existing multi colour printers, so you can’t “just mix” them as this would need additional hardware