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After encountering extreme under extrusion on my Anycubic i3 Mega, I first cleaned the nozzle and ended up replacing the entire hotend + nozzle. Since that did not help and I couldn't see any issues with it, I went on to check my E-steps. It seems that this is the root cause of the issue.

I removed the Bowden tube to have no resistance and used G1 E100 F100 to feed 100 mm of filament through the extruder. The extruder only extruded ca. 23 mm though, so I had to adjust the E-Steps value from 92 to 398 which already seemed way off, seemingly "fixed" the issue though. When I repeated the test "under load" with the Bowden tube connected and the hotend heated to 220 °C (using PLA I normally print at 200 °C), the extruder once again only extruded a fraction of the supposed 100 mm (I don't remember the exact measurement, though approximately 30 mm). The gears seem to be fine, and the filament that is pushed against the small gear doesn't seem to slip either.

Unfortunately, that's where my experience ends, can someone tell me how to proceed to narrow down the issue? I suppose it could be the motor itself, a faulty stepper motor driver, loose cables, or the mainboard.

Edit to @Citadel: When I bought the printer it had a spare hot end that came with it. I simply replaced the old one with this one. I did not do any further hardware customization.

Edit2: Sorry for the late update, I wasn't able to check the printer before due to work. I swapped the stepper driver with one of the others on board and checked the e-steps again. Aaaand I just then I noticed I must have forgotten to save the to eeprom when I updated the e-steps last time... So of course I tried with the swapped stepper driver and original e-steps (92), but this didn't fix the issue. So the issue is not the driver. After that I changed the e-steps to 398 again and saved this time. Last time I accidentally started a print that that caused the eeprom reset before I saved the settings and tried the e-steps under load. This time it worked, even under load. I still believe this must mean that the motor is missing some steps but for now it seems to print fine. If I get issues again I'll next try to swap the motor. Thanks for your answers!

TL;DR: forgot to save the new e-steps due to starting a calibration print that reset the value before saving. New value actually works but probably indicates that something might be wrong with the motor as the stepper driver is fine.

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    $\begingroup$ Easy first step would be to swap the extruder motor with another and see if the problem follows the motor. $\endgroup$
    – allardjd
    Nov 7, 2022 at 23:17
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    $\begingroup$ Depending on the machine architecture, it might be easier to swap a motor driver board. Some are integrated, some are modular. I'm not familiar with that printer. $\endgroup$
    – fred_dot_u
    Nov 7, 2022 at 23:20
  • $\begingroup$ After you first had the under extrusion, what was the hardware failure that required replacing the hotend assembly? What new hotend assembly did you buy? Did you remove the Bowden tube because you began using a direct drive hotend? $\endgroup$
    – Citadel
    Nov 9, 2022 at 1:22
  • $\begingroup$ okolaris, could you edit your question and add the info that @Citadel has requested? Thanks in advance. $\endgroup$
    – Greenonline
    Nov 9, 2022 at 17:55

2 Answers 2

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Make sure that you do not have volumetric extrusion (E in mm3) enabled in the printer's menu system.

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  • $\begingroup$ Thanks, for the reply! Are you talking about the M200 command in marlin? $\endgroup$
    – okolaris
    Nov 13, 2022 at 19:56
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    $\begingroup$ @okolaris Not exactly. A common error is to accidentally enable volumetric extrusion in the printer's firmware, but to have the slicer set for linear extrusion. This will cause massive under-extrusion. Another common error that will cause massive under-extrusion is to set the filament diameter in the slicer to 2.85mm (Cura's default value), when your printer uses 1.75mm filament, but this has nothing to do with volumetric extrusion. $\endgroup$
    – Mick
    Nov 13, 2022 at 20:47
  • $\begingroup$ That sounds plausible. Though I am not aware that the Anycubic i3 Mega has such kind of setting in the menu. I couldn't find any info on this either apart from the mentioned Gcode? $\endgroup$
    – okolaris
    Nov 13, 2022 at 20:58
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Using a Bowden drive system, you should never need to resort to testing the drive system without the Bowden tube. The tube acts as a neutral surface that retains the force of the plastic through the hotend. Try replacing the nozzle and fully cleaning the hotend following a YouTube video. If you don't have a hotend motor with a set gear, please test the uniform turning of the gears to see if the gears are slipping on the motor.

Make sure the Bowden tube is not clamped flat in any area. 220 °C is fantastic for PLA testing.

Please check out The almighty word of the 3d printing gods regarding underextruding and use it to become a better print mechanic and to be forgiven of your 3D printing sins. This reference holds dominion over all printers in existence, wield it responsibly.

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    $\begingroup$ Hi Citadel and welcome to SE.3DP..! :-) Try not to put follow-up or clarification questions in your answer (as this might lead to the OP try to use the answer section as a follow up post with more detail). Any requests for clarification and extra info should go it the comments under the question, so that the OP can edit their question and add the info there. However, as you need 50 rep points (you are nearly there!) to leave comments I have stripped the questions from your answer and put them as comments for you. :-) $\endgroup$
    – Greenonline
    Nov 9, 2022 at 17:48
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    $\begingroup$ However, if you wish to edit the questions (that were at the top of your answer) into statements of fact, then please feel free to do so. Also, whilst linking to external sites is fine (for reference), the main points from the link should be included in your answer itself. This is because should the link die (see link-rot) then your answer won't be as useful. $\endgroup$
    – Greenonline
    Nov 9, 2022 at 17:53
  • $\begingroup$ Hi, thanks for your reply. As stated in the post, Bowden tube, hotend and nozzle are new (got them included as spare parts when I bought the printer). $\endgroup$
    – okolaris
    Nov 13, 2022 at 19:42

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