First layer skips a few lines + starts to extrude blobs after a short period
 

[Solved] First layer skips a few lines + starts to extrude blobs after a short period  

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joachim.vdgoten
(@joachim-vdgoten)
Active Member

Hi,

If you look at the picture attached, I seem to have an issue where the filament suddenly stops extruding and then comes back after a few lines.

If I let the printer continue, the second layer only consists of blobs. I've been playing with the temperature and the z height. I've also ran the alignment wizard a few times. The first time I run it, I seem to correctly position the nozzle as it extrudes. The xtruded material seems fine. But when I run the wizard a second time, right after the first, I only see blobs being extruded. 

I've received this tip in a different topic:

Posted by: @an-prusa3d

Hi,

you picture does not show the same issue that we discussed here. You could open a new thread, because your picture is really helpful: It shows a repetitive pattern of underextrusion every X mm of filament.

Check your extruder visually without filament. Lift Z and do some purges or use "move axis -> Extruder" from the menu and see how or if the extrusion is inconsistent.

I noticed, that the pull force on the spool side of the extruder is weak and I had some failed prints since I printed from inside an Ikea Lack enclosure, through a filament guide (top table), out of a filament dry box. The pull force gets more and more on the spool side, less material gets extruded out of the nozzle, until the spool "snaps" and gives another few centimeters of filament. This happens all over again.

It could be a clogged nozzle but your pattern is so repetetive that I think you have some other issues going on here.

Greetings

@an-prusa3d

I only use the provided spool holder. But I did notice the occasional "pull" from the extruder. The filament is under a certain tension from the spool to the sensor. And then it pulls the filament in and the spool shifts heavily. The filament is then relaxed and the process repeats.

Support suggested to check the PTFE tube and if there was no gap between it and the nozzle. The PTFE tube itself seems to be out of tolerance. The same for the spare one that is deliverd in the box. They are both too short.

 

Best Answer by joachim.vdgoten:

SOLVED

The spring on the tension screw was not positioned correctly. I disassembled the extruder and while doing this the spring and srew fell out.

I put them back in the wrong way and this caused severe lack of tension on the filament. The spring needs to be put on the screw before putting it back in the extruder assembly.

Hard learned lesson but I am printing smoothly now.

Posted : 28/05/2020 12:24 pm
joachim.vdgoten
(@joachim-vdgoten)
Active Member

To give an update. Support is convinced that the cause is the PTFE tube that is too short.

They'll send me new ones.

I'll give it a try once I received it. If I have more news I will share it with you.

Posted : 28/05/2020 12:57 pm
crawlerin
(@crawlerin)
Honorable Member

If you want to try, disassemble hotend, clean it from remaining filament (cold pull or such), and assemble it again according to this guide https://help.prusa3d.com/en/guide/how-to-change-a-hotend-ptfe-tube-mini_119449/

It may not be a complete solution if PTFE is too short, but at least it can be a workaround to get rid of any gaps there, while you wait for new tubes to arrive. 

Posted : 31/05/2020 6:56 pm
joachim.vdgoten
(@joachim-vdgoten)
Active Member

I received the PTFE tube today and decided to test it out.

The first layer was ok, but not good. The next layers were a mess. As soon as it started printing the side walls it was fine.

Right until the top layers were printed. It all became a mess again.

It seems it has an issue with extruding while moving diagonally over the print bed. See attached.

Not sure if this is a PTFE tube issue, extruder issue, nozzle issue, ...

Posted : 03/06/2020 5:56 pm
joachim.vdgoten
(@joachim-vdgoten)
Active Member

This is the result of a cold pull I tried.

Doesn't look too bad.

 
And this is the result... Still doesn't work properly. 
 
This post was modified 2 months ago by joachim.vdgoten
Posted : 04/06/2020 8:54 am
joachim.vdgoten
(@joachim-vdgoten)
Active Member

SOLVED

The spring on the tension screw was not positioned correctly. I disassembled the extruder and while doing this the spring and srew fell out.

I put them back in the wrong way and this caused severe lack of tension on the filament. The spring needs to be put on the screw before putting it back in the extruder assembly.

Hard learned lesson but I am printing smoothly now.

Posted : 05/06/2020 8:40 am
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