<p>What you see on the outer surface is called "<a href="https://www.simplify3d.com/preventing-blobs-on-3d-print/" rel="nofollow noreferrer">zits and blobs</a>".</p>

<p>These small imperfections you experience are "zits" (larger ones are referred to as blobs). As the extruder needs to start and stop as it moves around during a print, it is difficult to create a seamless joint, so the over-extruded filament represents the location where the extruder started (or ended) printing a section of the outer perimeter of your print model. Sometimes it returns to the same spot in a single extrusion run, in other cases the perimeter is constructed of multiple sections.</p>

<p>It is possible to do something to minimize the effects depending on the slicer you use, but the general solution is to prevent too much plastic being deposited at either the start or the end of that seam. E.g. incorrect retraction settings may cause too much plastic to be extruded at the start, and pressure build-up in the nozzle may cause an excess of plastic to be extruded, both lead to the imperfections you experience. First you have to find out which of the two effects is happening with your prints. Once identified, you can play with settings like retraction, priming, and coasting to counteract on these imperfections. A more detailed description can be found <a href="https://www.simplify3d.com/support/print-quality-troubleshooting/#blobs-and-zits" rel="nofollow noreferrer">here</a>.</p>

<hr>

<p><strong><em>Edit</strong>:
Please read the addition posted in the comment by @Trish; the comment describes that this may also be related to over-extrusion!</em></p>

CC BY-SA 4.0
2018-07-08T10:07:38.243Z
I have experiences, that slight overextrusion also can result in only being visible at the point where the outer shell meets.
Trish
CC BY-SA 4.0
2018-07-08T12:06:20.580Z
@Trish Yes true, nice addition!
0scar
CC BY-SA 4.0
2018-07-10T03:47:23.373Z
Retraction speed is slow, retraction distance is high, wipe nozzle :/ ...
Fernando Baltazar
CC BY-SA 4.0
2018-07-08T09:47:34.183Z
2018-07-08T21:53:21.453Z
2018-07-08T21:53:21.453Z
0scar
<p>Your <strong>retraction-related setting &quot;Extra Restart Distance&quot;</strong> = 0.12 mm could be the cause of your issue, by using a too-high value.</p>
<p>I don't know which slicer you use, but it seems that this setting is the equivalent of &quot;Retraction Extra Prime Amount&quot; in Cura, there explained as follows:</p>
<blockquote>
<p>Some material can ooze away during a travel move, which can be compensated for here.</p>
</blockquote>
<p>So if retraction happens on layer changes in your case, then this setting could be too high, leading to the observed zits.</p>
<p>Indeed your value is quite high. It is equivalent to <span class="math-container">$\pi \times (\frac{1.75 mm}{2})^2 \times 0.12 mm = 0.29 mm^3$</span> (assuming 1.75 mm filament). Each of your zits is roughly a half cylinder of 0.6 mm in diameter and 0.35 mm in height, so <span class="math-container">$0.5 \times \pi \times (\frac{0.6 mm}{2})^2 \times 0.35 mm = 0.05 mm^3$</span>. It is easy to imagine that your 0.29 mm<sup>3</sup> extra prime amount could be too much by 0.05 mm<sup>3</sup>.</p>

CC BY-SA 4.0
2023-05-19T01:57:41.023Z
Yes, the problem in this question was entirely "extra restart distance" which is **always wrong** and should always be set to zero. There is simply no way that any constant value will do the right thing. I've even seen people with it "reasonably low" who had giant prints fail from nozzle collisions once they got to a part with lots of travel because the over-extrusion added up and had nowhere to go but up.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2023-05-18T21:09:28.960Z
2023-05-19T22:22:42.580Z
2023-05-19T22:22:42.580Z
tanius
<p>I have a Bowden extruder in my printer setup. Everything works great except this effect which must be related with retraction and is generated on Z layer change:</p>

<p><a href="https://i.sstatic.net/vasJH.jpg" rel="noreferrer" title="Print layer effect"><img src="https://i.sstatic.net/vasJH.jpg" alt="Print layer effect" title="Print layer effect"></a>  </p>

<p>The model itself, is printed in one layer perimeter / outline shell, with 0.25&nbsp;mm layer height with the following settings:</p>

<p><a href="https://i.sstatic.net/D66PI.png" rel="noreferrer" title="Printer settings"><img src="https://i.sstatic.net/D66PI.png" alt="Printer settings" title="Printer settings"></a></p>

CC BY-SA 4.0
2018-07-09T03:54:23.723Z
Turn off coasting. You should see some improvements right away.
electrophile
<print-quality><bowden>
What do you call this effect in 3D printing and how can I remove it?
OrElse
# What do you call this effect in 3D printing and how can I remove it?

(Asked by: username_0 on 2018-07-08)

I have a Bowden extruder in my printer setup. Everything works great except this effect which must be related with retraction and is generated on Z layer change:

[![Print layer effect](https://i.sstatic.net/vasJH.jpg "Print layer effect")](https://i.sstatic.net/vasJH.jpg "Print layer effect")

The model itself, is printed in one layer perimeter / outline shell, with 0.25 mm layer height with the following settings:

[![Printer settings](https://i.sstatic.net/D66PI.png "Printer settings")](https://i.sstatic.net/D66PI.png "Printer settings")

**Tags:** print-quality, bowden

> **Comments:**
> **username_1**: Turn off coasting. You should see some improvements right away.  

---

## 2 answers

### Answer by username_2 on 2018-07-08. Score: 4 | Accepted answer

What you see on the outer surface is called "[zits and blobs](https://www.simplify3d.com/preventing-blobs-on-3d-print/)".

These small imperfections you experience are "zits" (larger ones are referred to as blobs). As the extruder needs to start and stop as it moves around during a print, it is difficult to create a seamless joint, so the over-extruded filament represents the location where the extruder started (or ended) printing a section of the outer perimeter of your print model. Sometimes it returns to the same spot in a single extrusion run, in other cases the perimeter is constructed of multiple sections.

It is possible to do something to minimize the effects depending on the slicer you use, but the general solution is to prevent too much plastic being deposited at either the start or the end of that seam. E.g. incorrect retraction settings may cause too much plastic to be extruded at the start, and pressure build-up in the nozzle may cause an excess of plastic to be extruded, both lead to the imperfections you experience. First you have to find out which of the two effects is happening with your prints. Once identified, you can play with settings like retraction, priming, and coasting to counteract on these imperfections. A more detailed description can be found [here](https://www.simplify3d.com/support/print-quality-troubleshooting/#blobs-and-zits).

---

***Edit***:
Please read the addition posted in the comment by @username_3; the comment describes that this may also be related to over-extrusion!

> **Comments:**
> **username_3**: I have experiences, that slight overextrusion also can result in only being visible at the point where the outer shell meets.  
> **username_2**: @username_3 Yes true, nice addition!  
> **username_4**: Retraction speed is slow, retraction distance is high, wipe nozzle :/ ...  

---

### Answer by username_5 on 2023-05-18. Score: 3

Your **retraction-related setting "Extra Restart Distance"** = 0.12 mm could be the cause of your issue, by using a too-high value.

I don't know which slicer you use, but it seems that this setting is the equivalent of "Retraction Extra Prime Amount" in Cura, there explained as follows:

> Some material can ooze away during a travel move, which can be compensated for here.

So if retraction happens on layer changes in your case, then this setting could be too high, leading to the observed zits.

Indeed your value is quite high. It is equivalent to $\pi \times (\frac{1.75 mm}{2})^2 \times 0.12 mm = 0.29 mm^3$ (assuming 1.75 mm filament). Each of your zits is roughly a half cylinder of 0.6 mm in diameter and 0.35 mm in height, so $0.5 \times \pi \times (\frac{0.6 mm}{2})^2 \times 0.35 mm = 0.05 mm^3$. It is easy to imagine that your 0.29 mm3 extra prime amount could be too much by 0.05 mm3.

> **Comments:**
> **username_6**: Yes, the problem in this question was entirely "extra restart distance" which is **always wrong** and should always be set to zero. There is simply no way that any constant value will do the right thing. I've even seen people with it "reasonably low" who had giant prints fail from nozzle collisions once they got to a part with lots of travel because the over-extrusion added up and had nowhere to go but up.  

---

