Ender 3 - extruder stepper skipping

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I have a problem most likely very similar to some reported by other users: extruder stepper is visually skipping a step from time to time. It rapidly rotates in the direction opposite to the one it is supposed to rotate.

I noticed the following:

  • The extruder stepper jumps totally randomly - there is nothing specific in the pattern printed, position etc.
  • Stepper jumps more often on the infill, rarely on the walls.

Details about print:

  • PLA (Devil Design - various colors, they doesn't matter)
  • Filament guide installed on top, but not yet before the extruder (it is printing right now, I'm waiting for the ball bearings too)
  • Filament mounted on the top - in the place defined by Creality
  • Extruder is already replaced with the aluminium one
  • The mainboard is SKR E3 mini V2 (replaced recently)
  • 95% flow set in Cura
  • Printing on glass, leveled bed (the jumping occurs on all layers, not only first)
  • 215 °C hotend temperature, 60 °C bed temperature
  • Stepper motor current settings (from Marlin menu): 580 for X, Y & Z, 650 for E1

Other observations:

  • What's interesting is that extruder motor jumps even if I manually unwind some filament, so that the only force that it has to overcome is only pushing filament into the head.
  • I did a quick DIY wooden spool holder, so that the filament was fed almost horizontally. This actually seemed to make things worse - stepper jumped more often. I moved spool to the top again and it reduced jumping a little.
  • Prints are done beatifully (after changing the motherboard, that is) - no lost lines or layers, walls connected with infill, perfect first layer etc.

What may be the cause of stepper motor jumping? How can I solve it? Does it pose a threat to the motor or stepper? I need to print filament guide and spool holder with ball bearings, so that I can minimize force required by the extruder motor, but then the stepper will probably jump during the prints. I already damaged the original mainboard because of stuck filament, I don't want to destroy another one.


This is how regular extruder retraction looks:

(10 seconds)

This is how stepper skipping looks:

(13 seconds)


Today I replaced the whole heat block (radiator, heater, thermistor and nozzle) to a new one (original, for now) and motor stopped skipping - at least on the calibration cube. I will see, how will it perform on more complex prints.

However, even having the prior one in hands, I couldn't find the reason, why motor was skipping - other than the fact, that I couldn't extract the bowden tube from the radiator (so maybe some filament indeed was dripping inside?)

Spook

Posted 2020-12-12T20:40:03.983

Reputation: 141

How did you damage the mainboard from stuck filament? – R.. GitHub STOP HELPING ICE – 2020-12-14T16:00:46.577

@R..GitHubSTOPHELPINGICE, stuck filament increased resistance on the extruder - the extruder's gear's teeth became flattened at the level of filament. I suspect, that this might have caused the engine to stop sometimes and this - from what I know - would cause shorts on the engine controller. In the end of original motherboard's life the extruder was barely rotating - even if there was literally no resistance on filament (I was holding it in the air). – Spook – 2021-01-29T08:46:47.633

The bottom video shows that there is too much pressure build up (by compression of filament) for the stepper to handle, once over the tipping point, the stepper rotates back. Probably the initial resistance to overcome the stepper to rotate back is larger than when it has been set in motion, hence skipping back quite a distance. You should check your hotend, your temperature looks already quite high for PLA, or reduce print speed (don't know what that currently is). – 0scar – 2021-01-29T12:53:18.413

@0scar, the print is done at rate 50mm/sec with nozzle 0.4mm. However, this issue started when I replaced the motherboard and the extruder. At the beginning, with stock motherboard and extruder, printer printed even with speed of 60mm/sec without any issues. I bought a spare extruder motor to check, if the original one is not damaged.

Which part of the hotend do you suspect to be faulty? Clogged nozzle? Some other issues maybe? – Spook – 2021-02-02T08:12:47.007

Could be that the stepper doesn't get enough current? – 0scar – 2021-02-02T08:15:05.023

@0scar, how can I check that and possibly fix? – Spook – 2021-02-02T08:48:03.823

Answers

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I have a problem most likely very similar to some reported by other users: extruder stepper is visually skipping a step from time to time. It rapidly rotates in the direction opposite to the one it is supposed to rotate.

These two sentences are saying something totally different, and the latter is not what a skipped step looks like. It sounds like retraction, which is totally normal.

R.. GitHub STOP HELPING ICE

Posted 2020-12-12T20:40:03.983

Reputation: 5 311

Skipping happens regardless of the retraction. Also, retraction is fluid (stepper rotates) and the jump is rapid. Finally, jumps happen during drawing infill (like, in the middle of the line), so I hardly believe this is intentional behavior of the printer. – Spook – 2020-12-14T15:57:24.147

@Spook: Can you post a short video clip of it happening? From your question it sounded like the print still comes out ok. Is there underextrusion where the skip happens? – R.. GitHub STOP HELPING ICE – 2020-12-14T15:59:52.027

I just edited my question. Sorry for the delay. There are two videos: one with regular retraction and one with skipping. You can even clearly hear the "thud" sound when it happens in the second video. – Spook – 2021-01-29T08:53:16.773