Advise on colour bleed
I’ve got my MMU2S printing very consistently but I’m having some difficulty calibrating purge values. Problem I’m having is my purge values are are pretty high (Or so I think) and I’m still getting off colours in the print. Mainly the lighter colours although yellow to black slightly discoloures the back. In the picture attached I changed every value in advanced purge options to 250 (2 perimeters, 15% infill, no sparse layers). Do I just need to go higher or is there something I’m missing? The purge block is pretty large at these values and I see pictures on the internet and other peoples purge blocks are tiny compared to mine. Not only is it added time to the print, the extra material cost mounts up and I’m still not happy with the results. Not using cheap filament Either.
I've had results like that and I suspect it comes down to the shape of the hotend's cavities, and the temperature, which determines whether the unloading pulls out almost all of the filament (little purge needed) or leaves a blob (lots of purge needed).
What do the tips of the filaments the MMU unloads look like for you? According to the manual, they should be nicely shaped to the hotend, not having any melty look or string, but mine have always had strings.
Unfortunately the only real way to solve this is to increase the purge amount. Any light color printing after black, brown, red, blue, and green will need to have a massive purge. I usually set mine at 300 minimum.