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I have really strange problem. Thing is that my print (first layer) started ok, not good nor perfect but ok and everything was going well but then all of a sudden, near the end of a print, quality drops drastically. I'm not really sure but I think this happened because of under extrusion. I'm not so good with English so here are pictures of finished print and some more details.

enter image description here

enter image description here

I'm using custom build Delta printer with RepRap and Repetier firmware, CURA for slicing and Repetier-host for printing.

Slicing parameters in CURA are:
- ABS 250 °C hotend and 70 °C heatbed
- Layer height 0.2 mm (initial layer 0.18)
- Printing speed 50 mm/s (30 mm/s outer walls)
- Infill 40 %
- Extrusion multiplayer 0.96 (96 %)

Do anyone have any ideas? What this can be? How can I fix this?

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  • $\begingroup$ Is this towards the end of any print (regardless of height and size) or it is something that triggers at a specific z-axis height for all prints, or...? $\endgroup$ – mac Jan 10 '18 at 7:27
  • $\begingroup$ This doesn't happen on all prints, and it seems that this is height independent because it happens near the end no matter how high object is. $\endgroup$ – Rakic Jan 10 '18 at 14:47
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Do anyone have any ideas? What this can be? How can I fix this?

At least judging from the pictures, that does seem like under-extrusion. Some ideas for further investigating the issue.

The problem may be due to the gcode being wrong. In this case, your printer is merely executing correctly... the wrong commands. To check if this is the case:

  • The easiest, but inconclusive way, would be to re-slice a model that fails consistently, with a different slicer. If the second print came out good, than you would know that the problem is with the slicer. This method is inconclusive because you wouldn't not if the gcode is bad or if it simply happens that your printer cannot print well that specific sequence of commands (which may still be emitted by the other slicer under different conditions).
  • The more conclusive analysis would be to look at the gcode of a failed print where the fail happens between two geometrical identical layers. This seem to be the case for the print in the picture, btw. You should then compare the gcode of the layer that printed good with that of the layer that printed poorly. If the gcode differs... then you positively know the slicer doesn't work as it should.

The problem may be due to a mechanical fault with the printer. Here the only idea I have to offer is overheating of the steppers and/or their controllers. This may in turn make the extruder servo skip some steps and therefore extrude less filament. If you perform the conclusive test above, you will know if this is the case.

The problem may be due to a firmware bug. This is difficult to investigate, my only suggestion would be: upgrade to the latest and greatest, if you haven't done it already.

The problem may be filament-related. This could be a number of things, but since the problem seems to happen at towards the end of the print, and your are printing at relatively high temp, an idea could be that too much heat reaches the cold end of the extruder, interfering with its extrusion. The easiest test here would simply be to re-print a failed print with a different filament. In your case I would suggest some PLA, just to decrease the temperature and change the chemical composition too.

These are more or less all shots in the dark, but - together with asking here - it would be what I would do to debug, had I the same problem. Keep up posted! :)

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  • $\begingroup$ Firstly thank you for answer. I roughly checked Gcode for these few layers and there is no significant difference in E parameter. I also have decent cooling on motors and driver's so I think overheating have a very little change here, mechanical stability is not so good but shouldn't than all layers be bad? Firmware is upgraded, and last thing to try is decreasing printing temp to 230. $\endgroup$ – Rakic Jan 11 '18 at 0:22
  • $\begingroup$ @Rakic, actually reducing the temperature is the first thing to try, because it's way too high for your printing speeds. Also check that your temperature sensor gives correct values (ideally you have spare thermocouple) and is in contact with your hotend. $\endgroup$ – ZuOverture Jan 11 '18 at 3:15
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    $\begingroup$ Ok, so I just finished print successfully. I actually decreased temperature (from 250 to 230) and increase extrusion multiplayer a bit (from 0.96 to 0.98) and for now it seems to work. Thank you! $\endgroup$ – Rakic Jan 11 '18 at 17:42
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This doesn't look like a configuration error.

It seems very likely this is a partial hotend jam.

This happens sometimes because of stale filament but most often by not cooling down the heat sink (the part just over the heat break) enough which generates heat-creep, e.g heat creeps up through the filament, which eventually melts too early, creating a blob.

It's main characteristic is that at first the print is impeccable but after some amount of time, you get a complete jam or under extrusion.

This can be mitigated by higher print speeds, higher layers (so that the filament moves faster), printing at colder speed (if possible), lower retraction or usually completely solved with a fan cooling down the heat sink.

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  • $\begingroup$ I didn't know that, really useful information, thank you. By the way I already solved problem by lowering printing temperature. $\endgroup$ – Rakic Jan 11 '18 at 17:39
  • $\begingroup$ Good you fixed it! So it was most probably heat creep then ;-) Get a cooling fan for the heat sink, it will save you lot of trouble in the future! $\endgroup$ – Valmond Jan 12 '18 at 9:07
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I had a similar problem with PLA after upgrading to all metal hotend. My printer was in a cabinet and after some time in print had the same problem (heat creep). In the end, it was resolved by turning bed off after first 3 layers and turning on a fan to keep the cabinet cool.

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You can try to reduce your retractions (try setting it to half what it is now and try again)

If your retraction is too big you can pull hot plastic into the cold area of the hotend and create a partial clog - this happened to me yesterday when I tried to intentionally print with way too much retraction to make demonstration photos for the retraction test model I uploaded to thingiverse.

note/disclaimer: that model I talked about above is here, I'm the author of that model

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  • $\begingroup$ Good point but on this part of the print there is no retraction. I already solved problem by lowering temperature. $\endgroup$ – Rakic Jan 11 '18 at 17:37

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