Ok back at it after some relaxation away from 3D printers . So I noticed that in filaswitch, I had omitted extruder prime step when using purge bucket so the initial ramming length was too short to get a consistent good tip. Fixed the bug and did a rerun of the same benchy gcode as last time.
This time the print finished without a catastrophic tool change fail, although there a some evidently missed or at least partly missed layers seen. Also I ran out of blue filament right at the end so the roof of the benchy is incomplete.
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So there's still tuning to be done. Currently I'm experimenting with PTFE-lined 2x-feeder part. The idea is that PTFE-lining has less friction obviously so that would make the filament changes more reliable. Still the design requires cutting PTFE tubes and creating junctions which have some edges that might ruin the whole idea. But if this happends to work, I'll be chaining multiple of these to get to 6x material. This will also at least partially fix the problem with current big feeder part that's bulky and causes some stress on the X-carriage when all the PTFE tubes are attached to it, especially when the head is on the edges.
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Purge bucket: I really need to design a better way to store the waste material than just extrude it on the floor. If I would just throw it away, it wouldn't be that big of a problem, but I'm thinking about recycling all the waste parts I have so I want to save the waste for later. And having it on a long strings is definitely not the way to go because it needs to be cut to small pieces etc... for multi-material printing I'll probably just use purge tower for now, at least all the waste is in compact form and easy to store.