escher
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Extruder randomly retracting

Mar 10, 2019 5:11 am

Ever since I upgraded to the latest firmware and Slic3r on my MK2, I get random retractions on my first layer. If you watch the screw, you can see it skip backwards when it's supposed to be printing just a clear, flat line. You can see a gif at https://imgur.com/f06Ey0A. It won't embed for some reason.

If I make it through the first layer, everything will be fine for the rest of the print, but I'm only getting through the first layer maybe 10% of the time without these random retractions.

It's worth noting that I've tried four different filaments, and been through all sorts of tweaks on the longer screws keeping the tension on the extruder, but nothing seems to have made any difference. And, to be honest, watching the motor run backwards for a split second makes me pretty sure it's either in the software or in the extruder itself.

Any help would be greatly appreciated.

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tim.m30
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Re: Extruder randomly retracting

Mar 11, 2019 8:24 pm

The motor retracts filament when lifting the nozzle for some moves. Perfectly normal.

A better video would be of the part showing where the nozzle isn't extruding.

escher
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Re: Extruder randomly retracting

Mar 12, 2019 4:42 am

My point is that it shouldn't be retracting in this video: it's just going back and forth filling a flat base layer on the bed. But because it's retracting, instead of getting a clear line, I get gaps.

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tim.m30
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Re: Extruder randomly retracting

Mar 12, 2019 9:22 am

A photo of the part that isn't being printed correctly can also help.

Without looking at the slice, it is impossible to tell if retraction is planned or abnormal. If it's a simple square pattern sure, there shouldn't be much lifting, but if the part is complex, the slicer can do odd things.

That said, it's unlikely - but a bad Einsy motor controller could be wigging out. I'd do more testing to rule out simpler causes. Try printing this.

https://www.thingiverse.com/thing:2700178

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PJR
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Re: Extruder randomly retracting

Mar 12, 2019 3:25 pm

There's a few things that could cause this; here's a few suggestions:

Check the E motor cabling. Make sure it's not pinched between the extruder body and the X axis mount
Change the nozzle; there may be a partial blockage
Make sure you are not printing in silent mode (lower E-motor power)
Increase temp by 10 to 25 degrees (useful if your filament is damp or even wrongly labelled)
Ensure your filament feed is good and that the filament is not tangled on the spool
Clean your drive gears and check alignment with inlet and PTFE

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

alexander.s27
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Re: Extruder randomly retracting

Mar 12, 2019 6:08 pm

tim.m30 wrote:
Mar 12, 2019 9:22 am
Try printing this.
https://www.thingiverse.com/thing:2700178
Since this being a bed level test and the "retracts" most probably occuring during the 1st layer it could
well be that the live-z is too low.
With the above mentioned low-power settings and a too low nozzle a extruder-step-skip is most likely
which looks pretty well like a retract.
I wouldn´t exclude a broken cable or short what indeed was my 1st thought, too.
But that could be easily tested printing a small object (20x20x20 cube) and checking whether this still happens after the 1st few layers.
Provided a gcode we could have a look if that maybe comes from the slicer (which I believe not).

escher
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Re: Extruder randomly retracting

Mar 13, 2019 2:21 pm

PJR wrote:
Mar 12, 2019 3:25 pm
Check the E motor cabling. Make sure it's not pinched between the extruder body and the X axis mount
Change the nozzle; there may be a partial blockage
Make sure you are not printing in silent mode (lower E-motor power)
Increase temp by 10 to 25 degrees (useful if your filament is damp or even wrongly labelled)
Ensure your filament feed is good and that the filament is not tangled on the spool
Clean your drive gears and check alignment with inlet and PTFE
Thanks for all the suggestions!
  • I gave this a spot-check, but I'll look again tonight after work.
  • Nozzle is clear.
  • I am printing in silent mode, but I have been for the past two years without issue. I'll try in normal mode tonight.
  • I've varied both the temperature and the filaments to no effect.
  • Feed and spools are both good.
  • I cleaned the gears and everything looks fine.
From the next post:
  • I'll try with a higher z-level adjust and see if that has any impact. I may reset things and redo the leveling calibration as well.

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PJR
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Re: Extruder randomly retracting

Mar 13, 2019 3:15 pm

escher wrote:
Mar 13, 2019 2:21 pm
  • Nozzle is clear.
  • I am printing in silent mode, but I have been for the past two years without issue. I'll try in normal mode tonight.
When was the last time you changed your nozzle. For me, it's every 2 to 3 months.

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

escher
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Re: Extruder randomly retracting

Mar 14, 2019 4:54 am

PJR wrote:
Mar 13, 2019 3:15 pm
When was the last time you changed your nozzle. For me, it's every 2 to 3 months.
Interesting. I've never changed the nozzle at all.

New followup: I redid all the calibration, and it happens even during the built-in Z-level adjustment print. You can see the places that the extruder skipped here:
IMG_1425.jpg
IMG_1425.jpg (2.53 MiB) Viewed 65 times
This occurs on high power, auto power, and silent mode. It's worth noting that if the extruder is going to retract, it'll happen in roughly those spots on the x-axis. It also *always* happens at the end of the pre-print extraction at the front of the bed, in case that adds more information.

alexander.s27
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Re: Extruder randomly retracting

Mar 14, 2019 6:31 am

This really looks like a defect in the wiring, now!

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