Notifications
Clear all

Intermittent under extrusion?  

  RSS
Christian Matthews
(@christian-matthews)
Active Member
Intermittent under extrusion?

Just completed an upgrade from MK2s to MK2.5s a few days ago but am having some problems and am looking for some advice.

 

I am using Prusa Slicer and stock Prusa profiles. Printing at 0.15 Optimal with profile for Prusa PLA filament. Purchased a roll of fresh Prusa PLA (orange) as my existing stock is a bit old now. I have a fairly new 0.4mm E3D hardened steel nozzle fitted.

See photo attached.  Left, failed benchy. Center, idler cover (looks good to me), Right, same idler part failed with same settings as Center, printed directly afterwards.

What I seem to be seeing is intermittent under extrusion causing discontinuity between layers. This sometimes leads to an outright print failure. Other times things seem to rectify on subsequent layers but leaves weak adhesion between layers which make the part unviable. For reference, I have yet to successfully complete a benchy3D print, even an ugly one.

 

I have tried to be systematic and to investigate the usual avenues . Here goes...

 

Partial Blockage - I was pretty sure that this would be the problem. I was after all switching back to PLA from printing PETG for the upgrade on the mk2s. I put a length of Rigid Ink floss through the extruder at PETG preheat temperature. Loaded Prusa PLA and did a cold pull which was clean. I will note that I am currently getting some of the best first layer quality that I have ever had. I am sure as I can be that I followed the guidance on locking the PTFE tube firmly in place. I don’t *think* that what I am seeing suggests that there is a gap that is filling with melted filament.

 

Alignment - looks good. With idler door open the curvature on the filament means that it doesn’t drop directly into the PTFE tube, but with the idler in place it loads smoothly and positively. I think this is OK.

 

Tension - following the instructions in the video (link) I adjusted the screw to have enough tension for the filament to be pulled into the extruder just fine. Screw head is just slightly proud of the recess. The tension doesn’t *feel* that high. I did use the pull-through method for the captive nut. Have double checked and it is seated properly.

 

Retract Squeaking - I am getting horrible squeaking during retraction. I see that this isn’t uncommon with the ‘upgraded’ extruder. It isn’t accompanied by any clicking. My idler mount part from the upgrade turns out to have a bit of lateral flex between the shaft mount lugs due to slight delamination so I forced a bit of superglue gel into the crack and let it set. The flex is still there, in the order of a couple of hundred microns but it isn’t sloppy. I have applied a small amount of white lithium assembly grease on the idler gears (no, none on the surfaces which contact the filament facing surfaces).

 

Stringing - I don’t think I had ever seen a string on a print until recently and now I can’t print anything without spider silk thin stringing all over. I can burn them off, but I don’t understand why they are happening. I don’t think that this is a cause for the problem that I have but I include it for completeness.

 

So, after all that. Where do I go next? What have I missed, and what is worth further investigation?

Posted : 03/06/2020 11:41 pm
Christian Matthews
(@christian-matthews)
Active Member
Topic starter answered:
RE: Intermittent under extrusion?

I have been in touch with support who asked me to do some more cold-pulls. I have done another three, no obvious issue but will try again with Benchy at stock settings and see what happens. I was scheptical that this was a partial blockage but will be v.happy to be proven wrong.

Posted : 04/06/2020 2:46 pm
ARDI
 ARDI
(@ardi)
New Member
RE: Intermittent under extrusion?

I also experience under extrusion occasionally. Seems to be something MK2.5 has introduced because I have followed instructions meticulously when upgrading. It happens seldom but I'm completely at a loss as to why it happens. Filament slightly thinner in isolated sections and fails to be grasped by the extruder?

Posted : 27/06/2020 11:19 am
julian.p
(@julian-p)
Active Member
RE: Intermittent under extrusion?

I Also have been having extrusion issues.

I run Octoprint and noticed a significant hot end temperature drop when the part cooling fan turns on. The PID control of the heater tries to cope and return to nominal temperature but sometimes the filament cools too much and the nozzle blocks up. After this no amount of temperature tweaking will get the flow going again and I have to abort. Once it's all cooled, re-heating allows the filament to be removed and re-loaded and the problem goes away - until the next time the fan comes on!

I put a silicon sock on the heater block and it solved my problem. I think it must have something to do with the new part cooling shroud and the MK2.5s still having the 12V PSU.

We have three MK3s at work and they never do this, same hot end and shroud but 24V PSU

Posted : 11/08/2020 2:50 pm
Share: