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Layer shift, stringing & filament globs on larger print  

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José Rivera
(@jose-rivera)
New Member
Layer shift, stringing & filament globs on larger print

Hello all!

I got my Prusa running for a few months now and have printed PLA without much issue. I noticed some layer shifting on taller prints, but slowing down the print to 85% seemed to resolve it. However, recently I’ve been having some nasty layer shifts and globing when printing a desktop hydroponic system ( https://www.thingiverse.com/thing:5380016). Not too sure what the issue is. Following the filaments recommended settings, slowed the print down to 75%

Any thoughts or advice would be greatly appreciated. Thanks in advance for your time!

Posted : 19/07/2022 2:42 pm
Robin
(@robin)
Prominent Member
RE: Layer shift, stringing & filament globs on larger print

Usual suspects: loose grub screw on motor shaft and low belt tension. 

If at first you don't succeed, skydiving is not for you.

Posted : 24/07/2022 5:27 pm
Jose Rivera
(@jose-rivera-2)
Active Member
RE: Layer shift, stringing & filament globs on larger print

Thanks Robin - made some adjustments in the slicer settings that seemed to resolve the layer shifting issues. However, these blobs are out of control! I’m using a silicon sock to try to keep some of the heat off the PETG (Overture) but I have no idea what what’s causing this. I didn’t have this problem with PLA

Any thoughts is much appreciated!

 

 

Posted : 02/08/2022 7:15 pm
Robin
(@robin)
Prominent Member
RE:

My bet would be on a leaking hot end. That would also explain the layer shifts (blobs colliding with the object). Do you use normal mode with collision detection?

Can you post pictures of your hot end? Different angles, no silicon sock, complete heat block in frame would be helpful. 

PS I am printing PETG 90% of the time and have no blobs whatsoever without a silicon sock…

If at first you don't succeed, skydiving is not for you.

Posted : 02/08/2022 7:26 pm
Jose Rivera
(@jose-rivera-2)
Active Member
RE: Layer shift, stringing & filament globs on larger print

Will do - could that have been leaking from the factory? I never changed extruders

Posted : 02/08/2022 7:28 pm
fuchsr
(@fuchsr)
Famed Member
RE: Layer shift, stringing & filament globs on larger print

Have you changed nozzles? If not done correctly that can also lead to leaks.

Posted : 02/08/2022 8:42 pm
Jose Rivera
(@jose-rivera-2)
Active Member
RE: Layer shift, stringing & filament globs on larger print

Nope - haven’t changed nozzles - forgive my noob parlance, I meant nozzles instead of extruders.

 

I think Robin is right, I just don’t know what is causing the leak.

Posted : 02/08/2022 9:27 pm
Jose Rivera
(@jose-rivera-2)
Active Member
RE: Layer shift, stringing & filament globs on larger print

Update. Got 10 hours left on a print,  but look at this spent sock. It’s gotta be a hot end leak

 

Posted : 02/08/2022 10:06 pm
jsw
 jsw
(@jsw)
Famed Member
RE: Layer shift, stringing & filament globs on larger print

Leaks usually occur at the nozzle to heat break interface within the heater block.  (Diagram below)

There's really a lot of pressure on the molten filament, intended to squirt it out of a sub-milimeter hole, and if there's any other way for that molten filament to get out, it will find it.

I would suggest a good inspection of the hot end, looking for exactly where the molten plastic is coming from and, of course, correcting it.

The heat break and nozzle must make a tight seal, and there must not be any debris on the mating surfaces of those items.

Please pay particular attention to the gap between the head of the nozzle and the bottom of the heater block.

Posted : 03/08/2022 12:25 am
fuchsr liked
fuchsr
(@fuchsr)
Famed Member
RE: Layer shift, stringing & filament globs on larger print

I just want to re-emphasize one point @jsw made:

Please pay particular attention to the gap between the head of the nozzle and the bottom of the heater block.

It's important to note that this gap has to come about naturally as a consequence of the heat break being properly screwed into the heater block. In that case, when you screw in the nozzle, its end will meet the end of the heat break and a good seal is formed. At this point you can't screw the nozzle in any further and the gap is formed naturally. If the heat break sits too high in the heater block, the end of the nozzle will not meet the end of the heat break but instead the wider part of the nozzle will eventually hit the heater block without forming a gap. Manually creating a gap by unscrewing the nozzle not only won't help but is counterproductive as now you're creating a gap between the nozzle and the heat break through which material can escape. 

Obvious if you look at the diagram and know how the hot end works but I've seen a lot of people who don't get it, have a broken heat break installation, and are surprised while "leaving a gap" when they screw in the nozzle isn't working… 

Posted : 03/08/2022 12:39 am
Robin
(@robin)
Prominent Member
RE: Layer shift, stringing & filament globs on larger print

As we are emphasising stuff: Do not try to dis-/assemble a cold hotend! Tight seal does not mean high torque, do not use more than 2,5Nm to tighten the nozzle and 3Nm to loosen it.

refer to: https://help.prusa3d.com/guide/how-to-replace-a-heatbreak-heatsink-heaterblock-mk3s-mk3s-mk2-5s-mmu2s_16104

If at first you don't succeed, skydiving is not for you.

Posted : 03/08/2022 7:21 am
fuchsr liked
Jose Rivera
(@jose-rivera-2)
Active Member
RE: Layer shift, stringing & filament globs on larger print

Thanks very much for everyone’s input. After inspection of the hot end and review other posts on this forum its pretty clear that there is a hot end leak. Perhaps the tolerances became loose with use? I never changed the nozzle. I’m going to take this time to do so since I have to swap it out anyway. (I got a diamondback .4) Thanks again for all the help!

 

Here are some pictures with the sock off

Posted : 03/08/2022 1:46 pm
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