Lately, I've been having a problem with the surface of my prints. As shown in following picture:

enter image description here

Printing material is PLA. I've changed the print core (this is the terminology, Ultimaker uses for their hot end for e.g. Ultimaker 3 and 5; these cores come in different nozzle sizes and for different materials) but even with a different print core it happens from time to time (although less frequently). To me it seems like the extruded stops printing for a while and then continues. I've not been able to catch it while it happens though. Any thoughts?

  • $\begingroup$ What's the print temperature and bed temperature? $\endgroup$ – Trish Mar 8 '19 at 11:40
  • $\begingroup$ @Trish Bed temperature: 60 degrees Celcius, print temperature: 200 degrees Celcius $\endgroup$ – Chukke Mar 8 '19 at 12:22
  • $\begingroup$ My first two guesses: 1)clogging of the nozzle. What diameter opening are you using? 2) leaking somewhere in the hotend leading to droplets; this is less likely given the bad/missing layers that align with the blobs shown in the picture $\endgroup$ – Carl Witthoft Mar 8 '19 at 14:09
  • $\begingroup$ @CarlWitthoft I think you might be spot on with the clogging idea. Seems like no filament is extruding until a sudden burst of material is released? Nozzle size is 0.4 mm $\endgroup$ – Chukke Mar 8 '19 at 14:24
  • $\begingroup$ Have you printed a lot? Ultimaker advises to clean the extruder (it can contain shavings of filament grinding, don't open the extruder housings if you're not handy, they contain some parts that jump out when you open it and need to be at the correct place on assembly again), clean the tubes and clean the cores. Core cleaning is pretty simple, heat up the hotend an disconnect the Bowden tube on top of the print head and use some higher temp material like nylon to push/pull the filament out of the core. $\endgroup$ – 0scar Mar 9 '19 at 7:24

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