It occurred to me that one way to potentially eliminate all filament swap waste from purge towers or Bambu-style filament “poops” is to instead do something similar to a “purge object” or a “wipe object” but where the object is… filament.
The idea was somewhat inspired by Stefan’s video from a few months ago, which first introduced me to the idea of printing filament: https://m.youtube.com/watch?v=CQ-N1fr4N0w
If the purge object is new filament, then you don’t need to figure out what to use it for immediately; you can store the mixed-color filament for later use until you have a genuine need for a color-agnostic or structural object. No more piles of fidget spinners you didn’t really want.
A few other thoughts:
- The filament probably needs a minimum bend radius so it can feed into an extruder without breaking. One option would be to print a circle or a rounded square / squircle type of shape toward the perimeter of the build volume (potentially multiple concentric ones, or spiralized shapes). Another option would be to print disconnected straight segments.
- The filament doesn’t need to be printed flat. It could potentially spiral upwards (likely with supports). That could help avoid print head collisions for taller models (in which case you might not want the head to have to get back down to <1.75mm from the print bed). In the most general case, the filament could be printed at arbitrary angles, even vertically, and could start at some height above the build plate (potentially supported by the object itself, for example in an object where color changes don’t start at the very bottom). Maybe the angle could even be optimized to provide the best match between purge volume per layer and volume of new filament printed on each layer.
- A good solution probably requires a good way to connect multiple segments of printed filament together
- Mixing materials rather than just colors seems like a bad idea to me (e.g. soluble supports) but I’m going to mention it as a possibility anyway; you could conceive of something inspired by Stefan’s composite material and intelligently organize the different materials within your new filament.
- You could potentially control the mixes / transition colors that go into your purge filament, or even choose multiple different new filaments for different color transitions. For example, you might have separate new filaments for red-green, green-blue, and blue-red transitions. Maybe you want it create particularly pretty new filament, or avoid particularly ugly combinations.
I don’t actually have a multi-color / multi-filament printer, and I don’t have time to experiment with this (even though the first prototype could be as trivial using a filament shape as the wipe object in PrusaSlicer). I’m mostly sharing this to establish prior art in case someone nefarious seeks to patent something similar in the future (which is also why I added some half-baked thoughts that might make other things become obvious to someone skilled in the art), though it’d be great if the idea is actually good and someone could implement it well. Or for all I know this does already exist.
Thanks for taking the time to read this! Feel free to repost/share/steal the idea if you like it.
The diameter of your filament is extremely important for winding up with the correct amount of material extruded, because your printer does not actually know how much volume of material is being dispensed. All it knows is how much it has moved the stepper motor on the extruder, and the expected volumetric flow is simple multiplication.
Therefore, I don't think it's possible to print a filament in layers that will be sufficiently accurate, consistent, sufficiently round, nor feed safely and correctly especially if it were printed vertically, i.e. you would be pulling the final product into your extruder in such a way that it would be pulling against the layer lines.
Your recycled filament would surely have to be re-extruded in some capacity before reuse to ensure that it is both fully free of gaps and voids, is a solid contiguous piece, and is the correct diameter. You could print strips of roughly the appropriate size to be later fed into some manner of extrusion device to turn the material back into round filament of the correct diameter, though.
I agree that vertically-printed filament would have poor tensile strength, but isn’t most of the load from the extruder going to be compression, shoving it from the extruded gear to the melt zone and nozzle? Other than during retractions, doesn’t the tensile stress just comes from pulling the filament off the spool?
Well, in the interest of science you could try it and see. I predict various problems including but not limited to the teeth on your extruder wheel worming their way between the layer lines; the leaf springs on your filament sensor(s) that act as one way gates oriented so that the edge does not dig into the filament when it's being pulled in the normal direction, but instead biting hard into the layer lines of your printed filament on retraction operations; not least of which your filament diameter being extremely irregular if it's printed standing up.
I really don't think trying to purge filament into new filament completely in situ is feasible with the way current FDM printers work. The best we should shoot for is producing waste product that is easy to recycle externally, and coming up with better filament recycling rigs that are affordable by normal people to accomplish this.