Cracked filament
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I tend to print in short bursts with a long period of the printer sitting idle. When printing PLA, and with the printer having sat at least one or two weeks between prints, the filament ends up cracking. As far as I can tell, it is only that portion of filament that has been un-spooled and my suspicion is that the process of unspooling causes micro cracks and eventually the filament becomes brittle and breaks. For the longest time I thought this was only an issue with filament that was exposed to air since generally the section of filament that was in a feed tube would not exhibit the cracking issue.
Today I found myself needing to print a couple of items and found that not only had the filament in front of the feed tube cracked where it usually does but it had cracked in many many places inside the feed tube as well. I suspect it has been well over a month since my last print. The problem was that at every point where it was cracked, there was a slight kink between broken segments and the net effect was that the filament was pretty much stuck. I could pull out an inch or two from the ends but the center didn't budge because of very high friction caused by all the kinks/breaks.
I eventually managed to clear the feed tube but it was a substantial hassle since it had to be removed from the printer.
I am wondering if anyone has come up with a reliable method of preventing this kind of a thing?
A couple of points - the filament spool sits out in the open but I am in a very low humidity environment. While unloading the filament is possible, it is a hassle. I run four filaments so all four have to be unloaded. The more annoying problem is loading of the filament - there are a number of possible spots where the filament can catch and it becomes a bit of a pain to feed a single filament, never mind four of them. Spending 5 minutes on feeding a single filament is not unusual.
I would also like to point out that while I could possibly store the spools in a dryer box next to the printer, the end of the feed tube will always be open to the air and as I found out, cracking inside the tube is a thing.
Based on the fact that this is the first major case of filament getting stuck and previously it was only the exposed filament that had been un spooled that cracked, I am assuming it is a matter of air exposure after the filament was un spooled and presumably had micro cracks from straightening out the spool shape that had set in the filament.
I can have PLA sit out literally for months and months without it getting brittle but any section that was straightened at one time will become damaged in a week to two weeks.
Oh, I am running a direct feed extruder if that makes a difference.Thoughts ?
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@jens55 This won't help but I understand completely. I use multi input hot ends so have experienced exactly the same issues. I get it with ABS too although not as badly. Clear PLA is the worse of all - much worse than coloured.
I read somewhere on the internet that it's exposure to UV light which causes it but that won't cut it in my case because the printer sits inside a semi sealed booth inside my garage which has no natural light. The air inside that booth is kept at low humidity so the problem isn't moisture.
As you say, one can pull couple of metres off a spool and it'll print just fine without any breakages.
I think you might be on to something when you say it's the action of leaving the filament in a straightened out position. Presumably it's wound when it is freshly made and probably still warm which might set up stresses when it is unwound and straightened. -
@jens55 I have PLA spools sitting out for months, left on the printer, so theres like 0.5-0.7m of unwound filament. I have never ever seen such behavior where it would develop visible cracks on its own... Only seen PLA become really brittle presumably from absorbing moisture, but even then it looked fine, until you touched it haha.
PLA can be oxidized and it does reduce its molar mass, meaning it becomes more brittle and weaker, but I've only seen studies pointing out that this is an appreciable effect at 70ish degrees C, not so much below that point.
Could it be that you have some chemical vapor producing items nearby?
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I've had a very old spool (>4 years) of PLA that came with a used printer that disintegrated into 5-15mm long bits when I tried to feed it. Other filaments I have open for weeks/months without exhibiting brittleness.
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My setup is in the basement, no windows and no UV. Although leaving the filament in a straightened out position will necessarily hasten the cracking, I believe that micro cracks develop as soon as you unwind the filament and even if re-spooled, I believe the damage is done. I do believe re-spooling slows down deterioration as the micro cracks have a chance to closes - or more likely they don't expand more because the filament is relaxed again.
The cracks are not visible until the filament disintegrates
Most of the time the filament breaks close to the entry into the feed tube and it does so spontaneously without touching it. By the time the filament is in that state, looking at it funny will cause it to break. I highly doubt that chemical vapours are present at a high enough concentration in my printing area.
It does seem that some filaments are worse than others but every PLA I have tried does this to some degree. I have some ABS sitting in another printer that has been untouched for between 6 months and a year and there is no hint of the filament getting brittle.
