Sudden issues printing PETG - clumping, stringing
Clear all

Sudden issues printing PETG - clumping, stringing  

New Member
Sudden issues printing PETG - clumping, stringing

I am stumped on this one. Prusa docs and forum posts have helped me with every issue to this point but I could use some input on this as I feel like I’ve tried everything. 

I’ll try to summarize the problem and what I’ve done (sorry this is long winded, wanted to be detailed):

This is a gcode file I’ve printed dozens of times. I have made no modifications to it through many rolls of filament (including different brands) and have always had positive results. Right now I am using Overture PETG printed at 100% infill, 0.20 QUALITY settings in prusaslicer. 

The problem:

My prints are coming out with clumps of filament stuck to the sides and large amounts of stringing that has never been present before. It seems particularly bad near the corners of the print but is happening on the flat faces too.

[this is what happened as best as I can recall] On my previous roll of filament, I printed 3 of these parts without issue. I started having this issue during the printing of the 4th part. My printer is in an enclosure in the same room as my washer and dryer (I know… not ideal), and we ran a load of laundry during the print. I assumed at the time that the change in humidity caused the bad print.

But the 5th print on that roll had the same issue. Then I changed filament rolls (same brand, type, color) and had the same issue. That roll was unopened and stored in a separate room that does not see humidity changes before I opened it. I am still experimenting with that roll.

Here’s what I’ve tried:

  • I’ve had this roll in the dryer for days (50 deg at first, now at 60 deg). I am pretty confident it is not a moisture issue at this point. The dryer is reading 17% humidity.
  • I printed a temp tower and had the same stringing/clumping issues through every nozzle temperature 220-260, though it got worse at the lower temps. Compared to the part I'm trying to print, the temp tower was more stringy than clumpy.
  • I’ve replaced the extruder drive gear, hotend PTFE tube, nozzle, and all bearings (bearings probably aren’t relevant but I replaced them while I was in there) to try to rule some things out.
  • I’ve experimented with recommended retraction settings from other posts on the forum to no avail
  • I’ve tried raising the nozzle by changing the live-z with no change in results.
  • I’ve tried decreasing nozzle temp to 240 and increasing nozzle temp to 260 with no success.

Other observations:

  • The first layer seems to go perfectly. I say “seems to” because I see a lot of posts about the first layer causing issues, so perhaps I’m missing something. But I’m getting good adhesion and typically no gaps between the lines unless I’m experimenting with live-z. 
  • I had issues with the second layer before I replaced the nozzle. First layer printed fine but second layer would have random tears and holes. The new nozzle seemed to fix this issue with the infill part of the print but not the clumping/stringing.

I have not tried messing with the extruder tension screw, but I am having no problems with loading filament and not hearing any unusual extruder noises.

So the main issue now is the clumping and stringing that is happening. Again, this is a part I have printed for months now with near perfect results so I am at a complete loss for why the sudden difficulties. 


  • Should I try adjusting the extruder tension screw? If so, tighten or loosen?
  • Is it possible that it is a bad roll of filament, despite the filament being dry? I’m hesitant to blame the filament because it happened across two different rolls but I haven’t received my new shipment of filament to try out yet.
  • What else can I try?


Temp tower:

Examples of the carnage:

These last three photos specifically are when nozzle temp was 260:


Posted : 20/03/2023 2:46 am
New Member
Topic starter answered:
RE: Sudden issues printing PETG - clumping, stringing

For anyone that may see this in the future... I tried loosening the tension screw on the extruder. I backed it out a full turn, tested, then another full turn and tested and it seemed to help but not fix it. 

But... I was able to solve it, kind of. I ordered an E3D Revo Micro and replaced my hotend with that and I'm not having any more of these issues. I would provide more info if I could, but I'm still not 100% sure what was actually happening. I must have done something wrong with the nozzle or hotend ptfe installation. Or maybe there was a clog somewhere. 

So if your prints look like the images above, maybe check the hotend!

Posted : 24/03/2023 12:42 am