<p>This can be caused by various problems, of which an <a href="/a/7901/5740">aforementioned</a> filament diameter is only one of multiple possible causes.</p>

<p>The observed phenomenon is called <strong><em>under-extrusion</em></strong>. Temporary under-extrusion can also be caused by filament friction on the spool, too low or too high filament extruder gear friction (pressure on the filament by the roller), or friction in a Bowden tube (dust particles). </p>

<p>Please ensure your spool unrolls freely (not entangled; entangled filament is audible like "ker-chunk" when the filament is rearranged on the spool by force of the extruder pulling) and check the extruder for friction or slip. If the extruder gear slips, this is also accompanied by an audible "click" that is called clicking. This generally implies that there is too much friction in the hot end, or an obstruction/clog.</p>

<p>Considering that your print recovers from the problem, and that it occurs randomly, the best guess is that your filament in entangled now and then.</p>

CC BY-SA 4.0
2019-01-07T16:53:18.247Z
Thanks Oscar.  How do I check the extruder for friction and slip?  Is there a calibration process or similar for it?
BanksySan
CC BY-SA 4.0
2019-01-07T17:05:50.530Z
I just realised, I occasionally hear a loud "ker-chunk" which I'd attributed to the spool turning ungracefully around the holder.  I'm wondering not if that's when the bad layers appear.
BanksySan
CC BY-SA 4.0
2019-01-07T18:22:16.940Z
@BanksySan If you hear that, it means your filament is entangled on the spool, this causes extra friction, it is most probably your actual problem. Checking the filament that comes out if the extruder will reveal if you have too much or too less tension on the roller, you see that by the indentation the gear leaves in the filament. There are many pictures to be found on that topic. If you have a direct drive extruder you need to un-mount the hotend.
0scar
CC BY-SA 4.0
2019-01-07T18:38:02.330Z
@BanksySan Ker-chunk can also be a skipping extruder. It hints to a clogged nozzle often
Trish
CC BY-SA 4.0
2019-01-07T18:46:22.963Z
I've had similar problems related to friction in my bowden tube. The extruder will make frequent clicking sounds as it skips. Certain filaments seem more prone to this as well. I've found that lubricating the tube and/or filament fixes it. There are several sponge holders on Thingiverse; add a little cooking oil to the sponge and install it where the filament enters your extruder.
mbmcavoy
CC BY-SA 4.0
2019-01-09T12:31:11.030Z
@mbmcavoy Shortening the bowden tube a little also can help
Trish
CC BY-SA 4.0
2019-01-07T15:29:01.647Z
2019-01-10T05:12:49.423Z
2019-01-10T05:12:49.423Z
0scar
<p>One of the reasons for such a defect may be a local decrease in the diameter of the filament. Carefully check your filament.</p>

CC BY-SA 4.0
2019-01-07T17:04:34.023Z
Thanks Dmitry, what do you mean by _check the filament_?  It looks OK.  It's gray and long and thin.
BanksySan
CC BY-SA 4.0
2019-01-07T17:56:43.007Z
@BanksySan, measure the diameter of the filament with the micrometer or caliper in several points (>=10) on length about 5-10 meter
Dmitry Kasatsky
CC BY-SA 4.0
2019-01-07T18:02:03.367Z
@BanksySan, can you disassemble the extruder? The extruder gear can be loosely fixed to the motor shaft.
Dmitry Kasatsky
CC BY-SA 4.0
2019-01-07T13:45:52.863Z
2019-01-07T13:45:52.863Z
Dmitry Kasatsky
<p>I can print a reasonably high quality print, but then there will be a millimetre or two of rubbish.</p>

<p><a href="https://i.sstatic.net/9ppdc.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9ppdc.jpg" alt="Bad layer"></a>
<a href="https://i.sstatic.net/9kreD.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9kreD.jpg" alt="Bad layer"></a></p>

<p>This can happen at the start of a print, in the middle or at the end.</p>

<p>It doesn't seem to be bad G-code as I can reprint with good results.</p>

<p>There seems to be a correlation between the bad layers and walls.  They seem to occurs when there is a transition to printing a horizontal wall.</p>

<p>The latter if there two images if the tail end of a thirteen hour print.</p>

<ol>
<li>What's causing this?</li>
<li>Is it something I can fix or is it that the (new) printer is failing?</li>
</ol>

CC BY-SA 4.0
2019-01-07T13:00:25.090Z
that looks like 3 or 4 bad layers before recovery and then again... can you do a 2 cm diameter, 10 cm high pillar test print and check if that error always happens at the same height?
Trish
CC BY-SA 4.0
2019-01-07T13:34:43.193Z
@Trish I did some narrow cylindrical prints, 0.5 cm by 10 cm with a curved base for support.  The first failed the first millimetre then reduced, the second no failures (both had wobbly profiles but good adhesion).
BanksySan
CC BY-SA 4.0
2019-01-07T13:35:59.507Z
@Trish I'll print your recommendation, any specific settings that are good for a test print?  The prints above were 0.1mm layers.
BanksySan
CC BY-SA 4.0
2019-01-07T13:38:02.067Z
Thanks for the test. a larger diameter would allow to rule out thermal troubles with printing narrow objects (at some point they just blob). Just the diameter and some arbitrary hight that is larger than where you get errors is needed - if it always appears in the same hight on prints one after another it hints to the movement while random placement hints to extrusion. I suggest no infill and 2 or 3 walls - and no top layers
Trish
<print-quality><troubleshooting><quality>
Bad layers in otherwise good prints
BanksySan
# Bad layers in otherwise good prints

(Asked by: username_0 on 2019-01-07)

I can print a reasonably high quality print, but then there will be a millimetre or two of rubbish.

[![Bad layer](https://i.sstatic.net/9ppdc.jpg)](https://i.sstatic.net/9ppdc.jpg)
[![Bad layer](https://i.sstatic.net/9kreD.jpg)](https://i.sstatic.net/9kreD.jpg)

This can happen at the start of a print, in the middle or at the end.

It doesn't seem to be bad G-code as I can reprint with good results.

There seems to be a correlation between the bad layers and walls. They seem to occurs when there is a transition to printing a horizontal wall.

The latter if there two images if the tail end of a thirteen hour print.

1. What's causing this?
2. Is it something I can fix or is it that the (new) printer is failing?

**Tags:** print-quality, troubleshooting, quality
> **Comments:**
> **username_1**: that looks like 3 or 4 bad layers before recovery and then again... can you do a 2 cm diameter, 10 cm high pillar test print and check if that error always happens at the same height?  
> **username_0**: @Trish I did some narrow cylindrical prints, 0.5 cm by 10 cm with a curved base for support.  The first failed the first millimetre then reduced, the second no failures (both had wobbly profiles but good adhesion).  
> **username_0**: @Trish I'll print your recommendation, any specific settings that are good for a test print?  The prints above were 0.1mm layers.  
> **username_1**: Thanks for the test. a larger diameter would allow to rule out thermal troubles with printing narrow objects (at some point they just blob). Just the diameter and some arbitrary hight that is larger than where you get errors is needed - if it always appears in the same hight on prints one after another it hints to the movement while random placement hints to extrusion. I suggest no infill and 2 or 3 walls - and no top layers  

---

## 2 answers

### Answer by username_2 on 2019-01-07. Score: 2

This can be caused by various problems, of which an [aforementioned](/a/7901/5740) filament diameter is only one of multiple possible causes.

The observed phenomenon is called ***under-extrusion***. Temporary under-extrusion can also be caused by filament friction on the spool, too low or too high filament extruder gear friction (pressure on the filament by the roller), or friction in a Bowden tube (dust particles).

Please ensure your spool unrolls freely (not entangled; entangled filament is audible like "ker-chunk" when the filament is rearranged on the spool by force of the extruder pulling) and check the extruder for friction or slip. If the extruder gear slips, this is also accompanied by an audible "click" that is called clicking. This generally implies that there is too much friction in the hot end, or an obstruction/clog.

Considering that your print recovers from the problem, and that it occurs randomly, the best guess is that your filament in entangled now and then.

> **Comments:**
> **username_0**: Thanks Oscar.  How do I check the extruder for friction and slip?  Is there a calibration process or similar for it?  
> **username_0**: I just realised, I occasionally hear a loud "ker-chunk" which I'd attributed to the spool turning ungracefully around the holder.  I'm wondering not if that's when the bad layers appear.  
> **username_2**: @BanksySan If you hear that, it means your filament is entangled on the spool, this causes extra friction, it is most probably your actual problem. Checking the filament that comes out if the extruder will reveal if you have too much or too less tension on the roller, you see that by the indentation the gear leaves in the filament. There are many pictures to be found on that topic. If you have a direct drive extruder you need to un-mount the hotend.  
> **username_1**: @BanksySan Ker-chunk can also be a skipping extruder. It hints to a clogged nozzle often  
> **username_3**: I've had similar problems related to friction in my bowden tube. The extruder will make frequent clicking sounds as it skips. Certain filaments seem more prone to this as well. I've found that lubricating the tube and/or filament fixes it. There are several sponge holders on Thingiverse; add a little cooking oil to the sponge and install it where the filament enters your extruder.  
> **username_1**: @mbmcavoy Shortening the bowden tube a little also can help  

---

### Answer by username_4 on 2019-01-07. Score: 1

One of the reasons for such a defect may be a local decrease in the diameter of the filament. Carefully check your filament.

> **Comments:**
> **username_0**: Thanks Dmitry, what do you mean by _check the filament_?  It looks OK.  It's gray and long and thin.  
> **username_4**: @BanksySan, measure the diameter of the filament with the micrometer or caliper in several points (>=10) on length about 5-10 meter  
> **username_4**: @BanksySan, can you disassemble the extruder? The extruder gear can be loosely fixed to the motor shaft.  

---

