Started to print "Spongy" layers
I kicked off a print last night and it went well for two hours and I thought it everything was fine but when I woke up I found the print had "completed" but the top half was a "spongy" consistency. The general form of the model was correct but it just wasn't solid. The model looks fine in the slicer and I am not doing anything unique.
I did kick off another print but it still printing "spongy", even from the start now.
It didn't seem like stringy problem and aren't sure how to even search for this type of problem. Any ideas on what in the world happened? Any advice is welcome.
Michael S.
RE: Started to print "Spongy" layers
I just woke to the exact same problem! Mine is nylon, giving me no end of grief. I am playing with idler tension, it was tight (somewhat spongy result), so I went to very loose and got an even spongier result, the print actually stopped without finishing and the filament had a crack in it, I guess it jammed up? I am now trying again with about 0.5mm screw head protrusion. So many variables, what a pain!
RE: Started to print "Spongy" layers
That looks like under extrusion caused by a partial nozzle clog. Read up on doing cold pulls to clear the nozzle from the inside. I recommend using cleaning filament, but you can use other filament types.
I am not a fan of trying to clear partial clogs using needles or bits because you can damage the opening around the nozzle which can result in fine stringing.
If this happens repeatedly, you might need to bump your temperatures slightly. It looks like the filament flows nicely at the start but starts to clog up as it gets higher. A bit more heat can help with flow. Reducing speeds and retractions might also help.
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RE: Started to print "Spongy" layers
Not sure about original poster, but I have done daily cold pulls debugging this, I don't think it's a clog unless they are forming regularly. On nylon, I've seen people recommend large retraction settings (like 2mm), the Prusa default is 0.8mm and when I tried to increase it (twice) it jammed up and seemed to break the filament above the idler. Does that tell anyone something about whether my idler screw is too tight, or loose?
RE: Started to print "Spongy" layers
Have the same problem!
Cant solve it tried everything, even 10 cold pulls in a row to be sure... I tried to do multiplier calibration extrusion afterwards, and this is the result (picture) at start it is ok, then BS happens. I tried also to replace nozzle (0.4 for new 0.4) no help. 
RE: Started to print "Spongy" layers
Wow. Well, I can't tell if that's the same issue as mine, "sponginess" was a surface texture issue (holes and fluffy stringy voids), but this is just walls. I would say that in your case all bets are off after the wall loses integrity, so you can ignore the top part probably. What is that lowest failure, I can't tell? Is it too melted and loses form, or not adhering and loses integrity?
For now, I gave up on the .25mm nozzle I was trying to use and went back to 0.4, spongy issues went away. I can add that I learned the extruder idler tightness has a sweet spot and you need to be in it or things go bad.
RE: Started to print "Spongy" layers
Its actually sponge, but sometimes it creates a blob, I believe the sponge is underextruding (by caused by uknown element) then suddenly everything is pushed at once creating blob, and it is repeating. I was printing 40x40x40cube spiral vase (for precise filament extrusion calibration). This happens on all of my prints. I cant basically use the Mini anymore.
These clicking and underextrusion happens almost anytime. Tried various filament, temperatures, cleanup extruder gears, everything in a path of filament and no damn help...
RE: Started to print "Spongy" layers
Clicking, you say? Quick thoughts:
- make sure nothing is pulling on the feed line
- make sure the idler gears turn freely, and clean and lube as per Prusa forums
- play with that idler screw (screws? not sure how the Mini works) to see if more loose or more tight works.
- I think it's possible to have misalignment between the idler gears, and that PTFE tube, and the other parts down to the nozzle. I think a gap, or too tight, can cause this.