I recently started swapping out my nozzle for different sizes. After a few times using a 0.4 mm, then 0.8 mm, then back to 0.4 mm, I now have this "clumping" going on when printing. The photos are of PLA but this happens with PETG also. Before I started changing nozzles, my prints were perfect.

The blue filament is Overture PLA, printing at 45 mm/s 210 °C (I lowered the temp to 200 °C and it's still happening).

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Some things I've noticed (which did not exist when my prints were good):

  • Melted filament on the rubber piece that covers the underside of the extruder. Could something be backing up, melting, and then falling in a clump on top of my print?

  • The bottom metal piece on the extruder is slightly loose. It's the flat piece attached to the main extruder body with two screws. I don't know what it's called, so I couldn't even search for how to tighten it.

The questions:

  1. Does this "clumping' have an actual name?
  2. What did I potentially do when swapping nozzles that could have caused this (if that's in fact how it started)?
  3. How can I fix it?


The print stopped and I removed the shroud. My train of thought was spot on as I saw a pool of blue PLA inside the housing and on the nozzle. But I still don't know how this happened.

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  • $\begingroup$ Looks to me like the bed level is just too high and there's thereby more material extruded than fits in the space. $\endgroup$ Jun 2, 2020 at 17:40
  • $\begingroup$ @R..GitHubSTOPHELPINGICE I added an update, does it concur with your line of thinking or are we now at a different problem? $\endgroup$
    – Shades
    Jun 2, 2020 at 17:43
  • 2
    $\begingroup$ That means you have at least one other major problem. Probably the nozzle was not properly tightened and material exited at the gap. Having the pressure of the bed being too high would have contributed, but you had a problem either way.. $\endgroup$ Jun 2, 2020 at 17:45
  • 1
    $\begingroup$ @R..GitHubSTOPHELPINGICE I had assumed nozzles from the same manufacturer were the same height, but I did need to lower the bed. And I tightened the nozzle as much as possible. Problem solved. Thank you $\endgroup$
    – Shades
    Jun 2, 2020 at 18:54
  • $\begingroup$ I've adapted these comments into an answer, with some additional content. $\endgroup$ Jun 2, 2020 at 19:12

1 Answer 1


From your initial photos, it looks like the bed level was too high, and there was thereby more material extruded than fit in the space. Even with an "identical" nozzle, the distances involved here are on an order of magnitude (less than 0.1 mm) that you're not going to get identical distance to the bed from one nozzle to another.

Further, as you found out following up, not having the nozzle tightened all the way will affect its height, and allow molten material to exit around the gap. It's always a problem not having your nozzle tightened all the way to make a good seal (I actually had nearly the same problem the first time I ever changed a nozzle), but having the bed too close probably made even more material ooze out at the gap due to backpressure.

Hopefully fixing these two things gets you back to printing right. It might be some work to clean out any material left in the hotend, especially if it worked its way around into the threads where the nozzle screws in. Be gentle if you have to clean that out further, since it's easy to strip the threads if you use abrasive tools, and then you'll be looking at replacing the heater block.


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