Extruder skipping and under extruding  

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Jason_M
(@jason_m)
Trusted Member

I’ve been chasing an intermittent extruder issue for the last few months now. 

I get random skipping leading to under extrusion. Sometimes I can get a 39hr print fine. Others I can’t print for 2 hours before it happens. 

so far I’ve replaced and upgraded the following 

titanium heatbreak (e3D)

nickle plated copper heatblock (e3D)

new 0.4 brass nozzle (e3D)

new heater cartridge (e3D)

new thermistor (e3D)

new ptfe tube and collet / clip (all e3D)

none of the above has solved the issue. 
the only thing left in the hotend not replaced is the motor itself. 

I am not sure if the motor can be causing the failures but at this point it’s all I have left. 

the tension screw is flush with the body of the extruder when unloaded. The grub screw on the gear is tight. I have also installed an extruder motor cooling fan as I first suspected heat creep, but this has not changed anything. 

this issue has happened with many different rolls of filament so I doubt it’s a filament issue. Same brand I’ve been using for the last 3 years without issue too. 

can a failing extruder motor or wiring cause this behaviour ? (Extruder clicking)

if anyone has any suggestions I would be happy to hear them, as I can’t continue to throw more money at the problem. 

jason. 

Posted : 14/04/2021 10:43 am
egar
 egar
(@egar)
Estimable Member

The only time I've had the symptoms you mention (skipping, under extrusion, and extruder clicking) is when I have had a partial clog in the nozzle.  You've replace all of the hot end components, but you still have the issue.  Could this potentially be a filament issue?  Are you using the same filament or type of filament in all of the situations where extruding is giving you trouble?

 

Posted : 14/04/2021 3:10 pm
Neophyl
(@neophyl)
Famed Member

The clicking is the bond tech gears slipping on the filament usually.  That would indicate that the extruder motor has enough torque so it’s very unlikely to be the motor. 
Have you cleaned out the hobbed teeth on the gears ? The bits that actually contact the filament to make sure they aren’t gummed up ?  Also you say the screw is flush with the extruder body ? On my older mk3 it protrudes a few mm out when tensioned so have you actually tried simply tightening it ?

Also check the bond tech gear that is on the door, that the axle is in both sides, iirc the axle is short and can sometimes slip out one side which can cause feed problems. 
Beyond that I can’t think of anything else at the moment. 

Posted : 14/04/2021 4:04 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @jason_m

[...] I am not sure if the motor can be causing the failures but at this point it’s all I have left. 

You haven't described what print settings (layer height, extrusion width, speed) you're using, so this is a bit of a guess. Recent PrusaSlicer start gcode has incorporated extruder motor current adjustments based on layer heights. Unfortunately, as provided, these adjustments only apply to specifically formatted Prusa settings. 

I've made essentially the same hardware upgrades, and there's nothing you've listed that should cause problems.

the tension screw is flush with the body of the extruder when unloaded. The grub screw on the gear is tight. I have also installed an extruder motor cooling fan as I first suspected heat creep, but this has not changed anything. 

I'm still using the original Mk3 extruder. My tension screws protrude roughly 1mm normally. Inspect inside the extruder to see if you've got flakes of filament being ground off. Verify the idler gear spins freely.

this issue has happened with many different rolls of filament so I doubt it’s a filament issue. Same brand I’ve been using for the last 3 years without issue too. 

Do you notice any snags as you insert fresh filament? You might try opening the extruder up and verifying filament has a smooth path into the hotend. Also, inspect for any filament feed path issues. More than one person has been burned by a filament cleaning filter that would catch unpredictably.

can a failing extruder motor or wiring cause this behaviour ? (Extruder clicking)

Anything is possible, and weak(ening) motor would react similarly. I'd expect that to be a more pervasive problem, though. Have you done a PID tune since doing the hardware upgrades? Tried different nozzle sizes? Any custom slicer settings (e.g., jerk, acceleration) made?

Things I do when I get extruder clicking, more-or-less in this order:

  • Verify Maximum volumetric speed (rate) does not exceed hotend capacity. This depends entirely on the nozzle and print settings you are using. A 0.4mm nozzle can push roughly 11.5mm^3/s of PLA filament through the E3D V6 hotend used on the Mk3. Prusa uses 15mm^/s which is a tad optimistic IME. If you are using non-standard layer height, extrusion width, or speeds, you can easily push a bit above this which will cause skipping. You'll see this as the print moves into large infill areas that print at higher speeds. Quick test: Dial speed back 50% using the front knob. If the skipping stops, start by verifying your print settings are within spec.
  • Do cold pulls with cleaning filament (part of regular PM, especially when switching from higher-temp filament like PETG to lower temp like PLA).
  • Verify filament feed path is free of friction.
  • Check extruder tension screws (Bondtech feeder).
  • Inspect Bondtech extruder gears for wear and cleanliness.
  • Check Bondtech idler spins freely.
  • Check condition of PTFE tube (under Bondtech gear).
  • Confirm ambient printing temperature is < 40C.
  • Confirm airflow at extruder (around extruder motor). Check fan orientation and flow
  • Confirm airflow at hotend (part cooling fan). Check fan orientation and flow, verify fan is not blowing on heater block. Consider silicone sock. (Cooling fan blowing on block will cause problems.)
  • Do a PID tune, particularly if I've upgrade firmware or changed any hardware in the hotend.
  • Inspect PTFE at top of hotend. Verify not damaged below Bondtech gears.
  • Confirm thermal paste was applied to (and only to) top of heatbreak on assembly.
  • Increase nozzle temp slightly (workaround more for testing). If this works, try regular temp but with reduced cooling.
  • Verify retraction settings (particularly if the issue seems to be with small details). Does the problem seem to be associated with printing particular feature types?

These steps might help if your prints have lots of fine top details that cause intensive retractions. I resolved this  with the following settings under Printer Settings->Extruder 1->Retraction:

  • Adjusted Minimum travel after retraction to 2. (Prusa default is 1 which can allow a lot of closely-spaced retractions.)
  • Adjusted Retraction Speed to 50. (Faster retraction speed reduces stringing.)
  • Adjusted Deretraction Speed to 25. (Slower reduces hammering of filament back into hotend. YMMV.)

I found that if I calibrate my filament extrusion multiplier for each filament, I can use much more conservative retraction settings. I can use 0.2-0.4mm retraction, 0.4mm z-lift, and disable wiping completely.

 

 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 14/04/2021 4:09 pm
bobstro
(@bobstro)
Illustrious Member

Update: When the problem occurs, test the temp on your extruder motor. If it's getting hot, that can contribute to heat creep into the upper extruder assembly, causing lower-temp filaments like PLA to soften prematurely and deform in the extruder, usually between the Bondtech gears and PTFE tube. Try to diagnose why it's getting hot 1st (often retraction or ambient temps). Consider adding motor cooling (fans, heatsinks) as a last resort.

More notes here.

This post was modified 1 month ago by bobstro
My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 14/04/2021 4:20 pm
Jason_M
(@jason_m)
Trusted Member

Some good info there. 

thanks. I will check over stuff on the weekend. 

I should add I have a sock on the block, and I did the pid tune after the upgrade. 

also, I have a hot end extruder motor cooling fan attached as initially I suspected heat creep. The cooler uses a sunon fan. 

Also, new ptfe tube was installed when the upgrade was done. Heat paste was applied only to the heatsink side of the heatbreak. 

ambient room temperature is around 20°c so that should not be an issue  

filament loading and unloading is normal with no resistance or unusual looking tips  

this new hotend has had nothing but pla+ Through it  and a total of around 20 hours print time.

All print settings have been default prusa for pla at .15 layers and only changing the temps to suit my filament. 220 first layer 210 all others and 60 bed. 

I will go over the hot end again on the weekend looking at the suggestions posted here. 

hopefully I find something and solve the issue. 

thanks again 

jason 

Posted : 15/04/2021 2:48 am
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