Originally shared by Patrick Ryan
What fresh hell is this? New behaviour from a filament that’s always been pretty well-behaved in the past, on a printer that’s been pretty dialled in. It’s obviously cyclic in nature. Anybody seen anything like it before?
(Printrbot 1405 XL)
Some kind of problem on your extruder stepper motor?
I thought the same thing as @Michael_Vaughan when I saw the pic. Try bumping the temp up 5* and/or check extruder gear. I eventually found though that I had to replace my hotend and my wacky print problems went away.
I’m no expert. I’m one of those softies who bought a Replicator 2, so I only have a vague familiarity with the mechanics.
It’s repeating on what might be a one-revolution basis, which would mean something needs cleaning or re-aligning. I often do a warm pull (q.v.) on my nozzle when it’s getting wonky.
Dust on top of the filament roll? Moisture?
Hmm… some good ideas there, thanks guys. I think I might try bumping up my temp first, since that’s the easiest solution! 
Ah! I just looked closely at my extruder gear and noticed there’s a spot where it’s a bit gummed up with filament dust - maybe it ground the filament at some point. Wonder if that could cause a little slipping?
I have had that happen from time to time and I’ll use a very small, jeweler type screw driver to get in there and pick away at the filament within the knurled teeth. I think though that this slippage can also happen if you’re having problems with melting the filament. It shouldn’t take much tension to drive the filament through, but when I was having extrusion problems, I kept cranking up the tensioner thinking it was slipping at the extruder gear when the real problem was the temp of the hot end.
If the gear isn’t super-sharp, a toothbrush will usually do the trick. Of course, if you have a lot of gup that’s a sign something else bad is happening…
I’m relatively new to 3D printing but I’d guess 1) your print surface isn’t 100% flat, slightly domed 2) moisture in your filament. I’m doing a 5.5L Cake box mod to mine to keep the stuff moisture free after a batch I had stopped printing after a series of good prints the previous day.
Someone posted lately saying that the ir heated be was not stabelized in temperature and was raising and lowering as it heated and cooled resulting in Z ribbing. I imagine if you had such a problem it could cause this too. Of course, there are a number of things that could cause this. I just wanted to mention the possibility though.
Figured it out! Looks like it actually wasn’t temperature or a gummed up hobbed gear - I seem to have had my extruder idler tension too low. I’m guessing a very slight out of true on the round for the hobbed gear meant that at one spot during each rotation, the pressure against the idler dropped off enough that some slipping occurred.
Thanks for the suggestions!
Aha! I had that when I first switched over to a stepper-driven extruder. Cranking the setscrew on the drive gear was enough to make the gear just that little bit nonconcentric with the shaft. So the slipping was a symptom rather than a cause…
Oh. It was @Eclsnowman who spotted a heat bed temperature fluctuation that was causing a print surface height difference. If it was your hobbed pulley though, maybe you don’t need to bother looking for his post about it.
@NathanielStenzel I noticed that post, actually - but since I don’t have a heated bed installed at present, I’m guessing that’s not my current issue…
@Patrick_Ryan LOL I guess not then.
