Got the first prototype of the PTFE lined 2x feedert built and tested. Some details need to be tuned, but so far the results are promising. The filament path is a bit tight, I'm using Capricorn tube and the M4-nuts compress the tube also, even after opening the tubes with 2mm drill bit. But doesn't seem to matter, the 2x color Benchy had no issues with tool changes, they were seemed to work very smooth, no grinding of the gears or anything.
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The print has some blobs, smaller and bigger. The smaller are probably some retraction or filament related. The larger ones are happening from the head moves from the purge tower and continues printing the model and is realted to the tower retraction handling that filaswitch does. MY guess is that 2 things are happening:
1. the outer wall of the tower is printed quite fast up until the move back to model, causing bigger pressure on the nozzle and the default retraction isn't enough in this case.
2. S3D does retractions partly wiping during the retraction so the effective retraction is probably more than just a normal retraction. Filaswitch doesn't do that and I think I'm not going to implement that as it involves quite a lot of gcode ananlysis. However, this wipe-retract might also show as a discrepancy in retraction in model vs. the tower.

I updated the filaswitch code to slow down printing of the wall. I'll also add option add extra length to the tower retract so it can be fine-tuned better. Currently printing another benchy and it already seems better even with only the wall speed tuning done.

Oh and my MMU2S is finally shipped, nice