Parametric printable custom filaments (color blend, gradient, etc)

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Inspired by a similar (but restrictively-licenced and non-parametric) model on MakerWorld provided only in a few pre-made variants, I've created parametric printable filaments for color blending and other interesting designs.

You will need at least some basic ability with OpenSCAD to make much use of these. While I have uploaded prebuilt files, these are a very small size and are mostly intended as demonstrations. You don't need to know how to actually write OpenSCAD code, but you should at least be comfortable generating STL files from SCAD files and modifying parameters (including dealing with parameters that are spread across multiple files).

Demonstration images show the Gradient filament, three colors, 75mm color cycle length, made using eSUN PLA+ magenta, cyan and yellow.

General Forewarning
This kind of thing is obviously very much outside the intended use of a 3D printer. I accept no moral or legal responsibility if it breaks your printer, voids your warranty, or frightens your cat. (This doesn't mean I don't want to hear about any potential improvements or that I won't make them; it just means I'm under no obligation to do anything about problems that arise.)

All testing so far has been done with PLA on a smooth PEI build plate (except for a very limited amount of mixed-material testing), on a Flashforge AD5X equipped with a 0.4mm nozzle. (I will likely test with other nozzle sizes at some point - I have all four - but haven't gotten around to doing so yet.)

Also, the filament lengths stated by OpenSCAD in its output are estimates only. They are not completely precise - in my testing I have found they're in the right ballpark but are slightly off. If you know you need a certain length, always generate slightly higher than that.

General setup
You're going to want to print this on a fairly decent printer, and if you don't have automatic levelling, you're going to want to level the bed fairly well. The outcome is fairly tolerant of iffiness on the first layer (my yellow filament decided to be very poorly behaved on my first layer in the sample pics but it still worked fine), but anything going wrong on the middle layers can really mess things up. In terms of build surface - use a smooth surface if possible, although textured can work. Even more important, do NOT use adhesive substances like glue; you'll need to achieve good adhesion through your choice of temperatures and build surface.

Selecting combinations of materials
I have not yet found any situation where mixing two different materials is productive. Rather, this model is primarily useful for mixing different colors (or other attributes) of the same material. Color blending involves a lot of experimentation, but if you have access to the right color filaments, the CYMK model can be a good starting point. One key difference is instead of adding black to darken (although you can still do that), you'll usually be adding white to lighten. Gradients are pretty trial-and-error, but with the saving grace that it's pretty hard to make one that actually turns out bad. Another interesting use case can be mixing transparent glow-in-the-dark filament with colored filament - this can produce filament that when used, produces prints that look almost identical to the original color (especially with darker colors), but also retain a decent degree of glow-in-the-dark effect.

Notes on print settings
- Print temperatures: I find that these should be slightly higher (about 5 degrees on both the bed and the nozzle) than you'd usually use for the same materials.
- Layer height: Must match what was set in the SCAD file when generating the STL. If you're using my pre-made STL files, it's 0.1mm (including the first layer). I don't recommend going much higher than 0.1mm, and try to use something that divides evenly into the overall height of the model (which at the default settings is 1.7mm - so 0.1mm, 0.085mm or 0.05mm are good choices).
- Speeds: Go very slow for the first layer (I use 15mm/s). Your normal settings should be fine for the remaining layers.
- Walls: Arachne enabled if your slicer supports it, and Inside/Outside order. Aligned seams is usually better but Random may be worth trying on certain designs (in particular the gradient one).
- Infill: 100%, or even better, increase your wall count so that there's no infill
- Z-Hop: If your normal settings work fine, no reason to change them, but if you're having issues, try increasing this beyond “normal” range - I found 1mm works great.
- No brim (the model has a mouse-ear brim built into it already), no supports, no scarfs, basically no “fancy” stuff that isn't specifically mentioned above. You could try a raft if you really need it, I don't know how well it would work.

Notes on actually using the printed filament
- May need a bit more force than usual to load the filament. However, if it's more than slightly more than usual, your print probably came out wrong. Often this does come out slightly iffy near the ends; trimming the last 5mm away from each end is generally helpful.
- The printed filament is less flexible than real filament, but it's still flexible enough to wind on a spool. It's also still flexible enough for the multi-material unit on the Flashforge AD5X to handle; I can't make guarantees about any other printers or MMUs.
- You will almost certianly need to increase your extrusion multiplier (flow rate) a bit compared to the source filament. I personally found that when using a flow rate of 0.99 with the source filament, I needed a flow rate of 1.04 with the printed filament.

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Printable Filament Core.scad
This file does not generate anything in and of itself. It has some core functionality and settings that all of the other files depend on. You must download this file too in order to be able to use any of the others, and many settings (eg. the length of filament to create, layer heights, filament diameter, etc) are in this file. You can also use the functions here to code your own printable filaments.

Printable Filament Color Mixing.scad
One of the main attractions here; this can be used to blend colors you do have in order to create ones you don't. (Because, you know, it totally wouldn't be more logical to just fork out $20 or so for a professional-quality roll. But hey, sometimes you don't want to wait a few days for shipping, or you want a specific color that isn't generally sold, or maybe you want some combination like “glow in the dark + this exact shade of yellow”…).

Printable Filament Gradient.scad
Another “big one” - this one creates a filament that changes color as it goes along. You can alter how many colors it uses and how long the strands are.

Printable Filament Strips.scad
This is basically the “pro” version of the Gradient model - instead of just selecting how many colors and how quickly to rotate through them, this one lets you fully customize how far along the filament the colored sections start, end, and even how quickly they fade in and out. (Todo in a later update: Allow making the fade-in and fade-out rate different, without the need for tricky workarounds.)

Printable Filament Coaxial.scad
This one might be useful if you're experimenting with mixed materials, or possibly when combining glow-in-the-dark filament with solid color. It creates a filament that has a narrow core of one color (or material), surrounded by a “sheath” of another color. I mostly created this as a “first step” towards more complex designs than just “different layer is different color” and have included it simply because there's no reason not to - someone might find a use for it, and no harm is done by it being here. Note that this one especially benefits from the Arachne wall generator, I would not recommend trying this one on “Classic” (at least with a 0.4mm nozzle; might be more practical with a smaller one).

Printable Filament Solid.scad
This one simply creates printable filament in a single solid color. It may be useful if you want to run your printed filament through a second time (to get the colors blended a bit better) using this model, or as a quick test to see if your printer will accept printed filaments (instead of doing a slow multi-color print, just quickly print one of these with a short length and see if it works), or possibly for testing if you're making modifications to the core code.

I'm open to other ideas if anyone has suggestions - or feel free to make your own! And let me know if you find any interesting results.

Although the code for this model was written from scratch by me, the concept was heavily inspired by jetpad's similar concept model on MakerWorld: https://makerworld.com/en/models/460079-multi-color-filament-mixer