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I found my Ender 3 was skipping extruder steps a lot, mainly while printing infill (tri-hex at 30%), to the point I saw several layers of infill with spotty extrusion or nothing adhered at all.

When I pulled the filament, I had to use pliers to get enough grip to back it out of the hot end. I disassembled the hot end and found melted filament in the end of the Bowden tube, though I'm not sure that indicates heat creep, because I had to dismount the fan in order to reach the heat block and nozzle with the wrenches, and then preheat to get the nozzle out (meaning the heat sink got a lot hotter than it normally would with the constant blast of its fan).

Since the nozzle was full of melted plastic as well, I simply replaced it, made sure the heat break was clear by pushing the Bowden tube through it (and removed all melted plastic from the end of the Bowden tube), then reassembled the hot end with a brand new 0.4 mm nozzle. I then started a new print, gratified initially by the clean, even extrusion.

Until it stopped printing infill about 10 layers into the print.

At that point, I simply aborted the print and turned everything off, as I didn't have time to deal with another disassembly cycle (Sunday evening and had to be up early for work today).

What should I look for in trying to troubleshoot this issue with the nozzle or hot end clogging repeatedly?

I'm printing Amazon Basics PLA, a spool that was purchased the first week in May but only unsealed two days ago; my nozzle is set to 200 °C and the coated glass bed (now using a glue stick wash for adhesion assistance) at 55 °C. My nozzle clearance is set by homing, jogging the Z axis up by 0.075 mm, and leveling snug on a 0.08 mm feeler gauge (set so I can barely push the feeler under the nozzle and have palpable drag when in place, done with bed and nozzle preheated); this should give clearance between 0 and .005 mm. My first layer (standard 0.2 mm thickness) was perfect, no extruder step skipping and nice, even line width; this problem started only when the machine began to print infill -- infill prints faster than walls and top/bottom, but I'm not sure this is related to that, as I could see skipping on the walls on the second or third infill layer. This part was printing with 3 line walls and 30% tri-hex infill.

The Bowden tube was replaced when I installed a new hot end two weeks and ten or so prints ago (which included a new nozzle, the same one that I was using until yesterday); I made the cut in the PTFE with a tubing cutter (the kind with a wheel that revolves around the tube), so I'm confident it's square, and I ensured the tubing was butted firmly on the nozzle and the lock ring installed on the push-in coupler.

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  • $\begingroup$ Usually extrusion completely stops with heat creep. Does you Ender 3 still not have an enclosure? Thus, better heat sink cooling. Your description indicates that the Bowden tube fits against the nozzle. Have you verified that your heater-block termperature is correct with an external measurement? $\endgroup$
    – Perry Webb
    Jul 12 at 13:01
  • $\begingroup$ No enclosure. In normal operation, the tube coupler end of the heat sink is only warm (comparable to the heated bed temperature of 50+ C). I have no reliable way to externally measure heat block or nozzle temp, but I can't manually extrude PLA (by pushing the filament through a disengaged extruder) until nozzle temp reads about 185 C, so I don't think it's off by a lot. And extrusion stopping completely isn't far from where I'm at... $\endgroup$
    – Zeiss Ikon
    Jul 12 at 14:23
  • $\begingroup$ @PerryWebb Hmmm. And now, after sitting for almost 24 hours, I'm getting another perfect first layer. I wonder if it'll run five-plus hours this time, or if it'll start clogging again in a half hour or an hour? $\endgroup$
    – Zeiss Ikon
    Jul 12 at 22:10
  • $\begingroup$ ...and it finished the print nicely. The infill I saw before going to bed printed without a single lost extruder step (had a few in the second layer, but that cleared up on its own). I swear, this machine is haunted (and the part I'm printing is the last of the support brackets to immobilize the relocated power supply). $\endgroup$
    – Zeiss Ikon
    Jul 13 at 8:56
  • $\begingroup$ That sounds like heat creep. It sometimes happens when the extruder doesn't cool down before starting the next print. $\endgroup$
    – Perry Webb
    Jul 13 at 8:58
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I sounds like you are on the edge of almost heat creep if you start printing before the extruder cools off. See if letting the extruder cool down to near room temperature solves the problem.

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  • $\begingroup$ It occurred to me this morning that I had kept the machine preheated, bed and nozzle, for a longish time before printing that day -- I'll try switching to preheating only the bed (to ensure the glass is as warm as the thermistor reads the aluminum bed). It seems okay when actually printing -- filament flow soaks up excess heat -- but when idle and hot, there's nothing carrying that heat out the nozzle. $\endgroup$
    – Zeiss Ikon
    Jul 13 at 11:07
  • $\begingroup$ Starting from a cold nozzle before Print from TF", I've now gotten two successful prints (one 5+ hours, the other just over an hour) from the *same nozzle that clogged right after being installed. $\endgroup$
    – Zeiss Ikon
    Jul 14 at 13:03
  • $\begingroup$ I've seen the same need to let the nozzle cool before starting a new print when printing PETG. $\endgroup$
    – Perry Webb
    Jul 14 at 14:02
  • $\begingroup$ Got an all metal hot end on the way, should be here in the next week or two (from China) -- that should improve things some (I think). $\endgroup$
    – Zeiss Ikon
    Jul 14 at 14:12

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