Causes of over-extrusion?

1

What could be the causes of a consistent over-extrusion? I know about these:

  1. steps/mm of extruder motor set too high
  2. larger filament diameter
  3. slicer setting: filament diameter - setting it lower makes the printer extrude more filament
  4. slicer setting: extrusion multiplier - setting it higher makes the printer extrude more filament
  5. unlikely but possible bug in slicer or in printer firmware
  6. other: low/high tempereture, too much/little tension on the extruder gears, wrong nozzle fitted,...

Now to my problem. I had to replace the entire hotend assembly on my Prusa i3 MK2,5. Before that, there was no issue. After the replacement and after noticing the issue, I followed the list above. I recalibrated the extruder and in fact I had to increase the steps/mm to match the extruded length.

I have printed with different filaments and the issue is still present. Also I checked the diameter of all the filaments which are quite consistent (1,75 +-0,3 measured, 1,75 +- 0,5 given by the manufacturer). All of them were the same brand.

I also checked slicer settings and the default values that I used before were still there.

Slicer and firmware versions are the same as before the issue started occuring.

I use the same print settings as before and have checked the extruder gears tensioner multiple times over. The nozzle came with the hotend and according to the E3D dots it is in fact the default 0,4 mm nozzle. However, I cannot check the real diameter.

I know I can solve this issue by altering the steps/mm or extrusion multiplier because the over-extrusion is consistent. I want to know if there is something I am missing that could cause this.

Thank you for your valuable time and suggestions.

Edit: Image 1

Image 2

MStarha

Posted 2020-06-01T10:46:01.747

Reputation: 173

Did you ever find a solution to this? – R.. GitHub STOP HELPING ICE – 2020-07-06T22:23:52.903

No. I have once again tried recalibrating the extruder, this time I decreased steps/mm. As you have said, it is minor overextrusion so I might just roll with it. – MStarha – 2020-07-08T09:11:26.893

Answers

1

This is almost surely the source of your problem:

I had to replace the entire hotend assembly on my Prusa i3 MK2,5. Before that, there was no issue. After the replacement and after noticing the issue, I followed the list above. I recalibrated the extruder and in fact I had to increase the steps/mm to match the extruded length.

There is no plausible physical reason for extruder steps/mm to change due to replacement of the hotend. Steps/mm is purely a function of stepper motor steps per rotation and extruder gear radius. Set it back to its original value.

If the extruded length is not matching what it should, you have a problem with blockage/flow rate in the hotend restricting advance of the filament and causing the extruder gear to grind without moving it, or the motor to skip steps. Adjusting steps/mm to "compensate" will not fix this; it will just grind/skip more. Instead go back to the beginning, with steps/mm set correctly to the original value, and start looking for the cause of your hotend problem.

R.. GitHub STOP HELPING ICE

Posted 2020-06-01T10:46:01.747

Reputation: 5 311

I have disassembled and reassemled the assembly, recalibrated the extruder and still nothing. Also, your answer does not make any sense when talking about over-extrusion (it would make a lot of sense when talking about under-extrusion). A blockage in the filament path cannot increase the flow of the plastic consistently. It can do it repeatedly: pressure builds up in the fillament because of a blockage, when the pressure is large enough, the filament gets released, therefore momentarily increasing the flow of the material. But that is not what I am experiencing. My over-extrusion is consistent – MStarha – 2020-06-05T15:59:32.313

@MStarha: The overextrusion happened even before you made any adjustment to the steps-per-mm? You said you increased the steps/mm which absolutely would cause overextrusion. – R.. GitHub STOP HELPING ICE – 2020-06-05T16:03:14.403

Yes, it happened before the first extruder adjustment and after the hotend change. That's the problem, it was over-extruding even when in fact the extruded length was shorter than requested. – MStarha – 2020-06-05T19:52:11.003

What you're describing is physically impossible (less length at same diameter but more volume). Are you sure what you're seeing is overextrusion? Can you provide some pics? – R.. GitHub STOP HELPING ICE – 2020-06-05T20:41:47.703

Added pictures to the original post. I know it is not logical, thats why I am here. Cannot figure it out myself. The over-extrusion is subtle, but it is there. As long as it is there, I cant trust the dimensional accuracy. – MStarha – 2020-06-06T18:54:43.557

Are those with steps/mm reverted to original setting? Or increased? – R.. GitHub STOP HELPING ICE – 2020-06-06T19:38:10.853

I have not written down the original steps/mm. This is after all changes (first change of step/mm, dissassembly, reassembly, second calibration). It is what I have now. – MStarha – 2020-06-06T19:45:24.337

What is the value you have now? Can you not do a factory reset? The E steps per mm should be equal to (assuming a 1.8°/step motor and 16 microsteps) 3200/(pi*d) where d is the diameter of the gear. – R.. GitHub STOP HELPING ICE – 2020-06-06T20:08:26.553

The steps/mm value is 152,6. I might try a full reset, but if the end effect is only reduced steps/mm to compensate for over-extrusion, then I can set it manually. – MStarha – 2020-06-06T20:31:03.683

From the photo it looks like you have some fairly minor overextrusion and possibly a misleveled bed making it looks more severe on the bottom surface. If you're going to "set it manually", at least figure out first what the ideal value should be, based on the gear diameter, so that you know if your new empirically calibrated setting is theoretically over-extruding or under-extruding. – R.. GitHub STOP HELPING ICE – 2020-06-06T20:39:27.440

I will try to compensate for it with steps/mm then as there does not seem to be a problem with anything else. The issue with theoretical calibration is that you cannot measure the diameter of the gear since the teeth bite into the material. How much they sink in depends mostly on the material and the tension. I did a quick check and based on the step/mm value, the diameter would be ~6,6mm, which is possible. But anyways, thank you very much for your help. I will post an update. – MStarha – 2020-06-07T09:13:18.040

The gear should have a data sheet giving you an accurate measurement. And if it needs compensation for biting into filament, that's per-material so should probably be modelled in your slicer's material settings not changing esteps. – R.. GitHub STOP HELPING ICE – 2020-06-07T14:16:05.227