My multi-color/-material printers

[spegelius]

Printing ~3 years old PVA is a b!tch. PVA is a water soluble maerial, similar to BVOH but not as good. I bought a roll of FormFutura PVA some time during 2017 I think, with the intention of actually using it. Well after some tests the roll went to the back of my filament storage and was kinda forgotten, because with my first dual color setup, Prometheus, the results weren't very good. The PVA didn't stick too well to PLA and during filament changes it would break way too often when it was being pulled out of the nozzle.

But occasionally I have thought about using it, it wasn't cheap. Now that I have the MMU2S, I thought to give it another go. There was a mention somewhere that the roll should be used within 12 months, but f that.
So the first attempt resulted in a hotend jam so bad that I had to remove the nozzle and use 1.5mm hex to push the clog out. Was not fun. After that I did get it flowing, but there was intermittent popping and hissing and very uneven extrusion so I put the roll to the oven (~60c) for few hours since PVA seems to like to suck in moisture. This helped quite a lot, the filament flow is consistent with only very occasional pops I can't seem to get rid of no matter how long I let the roll cook in oven.
Actually doing multi-material printing with this particular PVA seems to be very time consuming, not sure if the filament has actually gone bad or if it's just this way. At first the filament changes would fail practically every time when switching from PVA to PLA. The PLA just jammed every time with extruder clicking or the gears eating a hole in the filament. I tried tuning the temperatures and ramming settings in PrusaSlicer for the PVA, but lowering the temperature just made PVA print quality worse, didn't help with the problem. After a while I ditched PrusaSlicer. I sliced the model with KISSlicer and post-processed it with filaswitch because in filaswitch I have much more control over the filament change sequence. After some tuning and retries I got it working quite reliably, with something like 8 to 1 success/fail ratio. The problem seems to be that the PVA leaves long strings to the nozzle after it's pulled out, which cause the PLA to jam.

The result is this, a hilbert cube printed with PLA and PVA https://www.thingiverse.com/thing:16343. I didn't use PVA as slicer generated support, instead I printed the main model with PLA and the provided 'support' model with PVA which is a solid block. I tried using PVA as regular supports, but that just resulted in a great big mess of bits of PVA all over the place. Printing solid stuff with this PVA seems to work better and actually results in better overhangs.

The print itself took some 8 hours of actual printing, but it happened in a span of 3 days. I had to babysit the machine all the time because of the high possibility of failed filament changes. Each night I paused the print in Octoprint and turned off the heaters and just continued the next day when I felt like it. Also I stopped the print at least 3 times, edited the gcode file by hand to change the filament change sequence and started the print with the new file. Luckily the machine doesn't loose track of it's position when print is stopped from Octoprint. Supprisingly all this worked, although there were a couple of issues that could have resulted in a fail.

Not sure if the time sitting beside machine was well spent. Still, it was mostly playing mobile games and reading a book, occasionally tending a clog which luckily was mostly just selecting 'Change filament' from Prusa's menu, cutting the tip of the PLA, refeeding the filament and continuing the print. Not that bad actually, especially when it's possible to pause the whole ordeal for longer periods of time.
IMG_20201010_161815.jpgIMG_20201011_121943.jpgIMG_20201011_121947.jpg

PVA isn't very fast to dissolve. The pic above is after the part had been soaked for about 12 hours. Apparently having the water flow would help. I think I have a aquarium pump somewhere, might try putting it in the vat to speed up the process. I'm also dissolving PVA in the purge block, I'm thinking about building a filament recycling setup in future so I'll be saving the waste.