<p>There are a few issues that could cause this. Roughness in your z-axis lead screw as pointed out by @TheLamestUsername is a leading contender I would say. I'd also extended that answer to include checking the belts for your X and Y axes as well as making sure that the rods the gantry slide on are smooth since the fault appears to be in about the same X-Y location as well in the one image.</p>
<p>However, there are a few alternatives as well. Check/confirm that the material that you're using doesn't have a lot of absorbed moisture in it. This can cause little bits of steam to 'pop' when they're extruded causing some bubbles</p>
<p>Because of how the material is folding at the location in the &quot;updated&quot; image this looks to be an issue with the starting and stopping. All of the layer's problems appear to be happening when the gantry moves up to the next layer. Essentially more material is coming out of the nozzle there (I think) than is what should be. Confirming material diameter with some calipers can help if there's just an offset (not too unlikely I don't think).</p>
<p>If the diameters are dead on I'd suggest reducing the nozzle temperature by a few degrees. The sensors used to measure the temperature aren't usually all that accurate, though their precision is often pretty good. While you may have it set at 200C that might not be the actual temperature. Calibration of the thermal sensors can drift over time, so while it might have been good on the last roll it may have drifted slightly. Or the material might be of slightly different composition. Try lowering the nozzle temp by 2-5 degrees and see if that has any effect.</p>
<p>You may also have a retraction setting that can be modified. Pulling the material back ever so slightly when it finishes the one layer as it moves to the next could alos reduce some of the extra material that's coming out.</p>

CC BY-SA 4.0
2020-10-14T17:22:01.473Z
2020-10-14T17:22:01.473Z
Diesel
<p>The fact that the bumps were in the same spots on multiple occasions points to z-axis problems. Turn your printer off and manually turn the z-axis all the way from bottom to top. If there are any tight spots, there is some <em>z-axis binding</em>. If there are no tight spots, skip to the last paragraph.</p>
<p>Try taking off the z-axis by removing the set screws (pictured below). Remember which side was pointing up for a later step.</p>
<p><a href="https://i.sstatic.net/GnC4r.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GnC4r.jpg" alt="enter image description here" /></a></p>
<p>Once you do that, clean the screw thoroughly with a brush, cloth, solution, or a combination of those. Put the screw back in the opposite way this time.</p>
<p>If you get no bumps, then it was indeed the z-axis</p>
<p>If the bumps are still there, try lowering your temperature some more(200 is still a little high compared to what I do for PLA), and <a href="https://all3dp.com/2/extruder-calibration-6-easy-steps-2/" rel="nofollow noreferrer">calibrate your e-steps</a> if you haven't already.</p>

CC BY-SA 4.0
2020-09-23T05:29:44.877Z
2020-09-23T05:29:44.877Z
Diatom
<p>First of all, I'm quite new to 3D printing. After printing some temperature towers, stringing and bridging tests, I wanted to print the Bechys to see everything working together. I'm getting some strange &quot;bumps&quot; in the outer walls. It looks like for 2-3 layers, the filament gets lifted up.</p>
<p><a href="https://i.sstatic.net/l0w83.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/l0w83.jpg" alt="infill before walls set" /></a></p>
<p><a href="https://i.sstatic.net/VNmNB.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/VNmNB.jpg" alt="infill before walls unset" /></a></p>
<p>I first thought, the infill is printed too far in the outer shell, so I unchecked &quot;Infill Before Walls&quot; in Cura. Surprisingly the outcome did not change and the &quot;bumps&quot; where in the exact same spots as before.</p>
<p>I am aware of a part cooling problem, but my stock cooler already sits at 100 %. I don't think, the extruder temperature is too hot, with it being only 200 °C. As you can see, the printer only has a one sided cooling solution with a very small fan conduct.</p>
<p><a href="https://i.sstatic.net/bOANt.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/bOANt.jpg" alt="fan conduct" /></a></p>
<p>Print settings:</p>
<ul>
<li>Printer: Anycubic I3 Mega S</li>
<li>Slicer: Cura</li>
<li>Material: PLA</li>
<li>Extruder Temp: 200 °C</li>
<li>Bed Temp: 60 °C</li>
<li>Print speed: 45 mm/s</li>
<li>Travel speed: 100mm/s</li>
<li>Layer height: 0.2 mm</li>
<li>Layer width: 0.4 mm</li>
<li>Nozzle: 0.4 mm</li>
<li>Infill: 10 %</li>
<li>Retraction distance: 4.5 mm<br />
Retraction speed: 40 mm/s</li>
</ul>
<p>So I am suspecting it must have something to do with the way, it is sliced. Does anyone have an idea?</p>
<p>Update:
I started the print again with aligned seams. Now you can clearly see the artifact. At the point of the seam the print is warped inwards and upwards.</p>
<p><a href="https://i.sstatic.net/TK9IT.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TK9IT.jpg" alt="aligned seams" /></a></p>
<p>I did some more prints and tried to increase retraction distance up to 10 mm and retraction speed up to 60 mm/s, but I also did not manage to improve the print. I also tried to enable the &quot;retract at layer change&quot; option and to disable &quot;Z Hop When Retracted&quot; but without success.</p>
<p>I set the travel speed down to 45 mm/s with no change in print quality.</p>

CC BY-SA 4.0
2020-06-18T16:37:43.110Z
Please slice with layer change aligned and post an image (20 layers should suffice), so that we can see if this is related to layer changes or not.
Davo
CC BY-SA 4.0
2020-06-18T22:00:17.990Z
Hi welcome to 3DPrinting.SE! What can be seen on the bottom photo is that your nozzle is a little too far from the bed, and you aren't using enough part cooling (see the overhanging bow).
0scar
CC BY-SA 4.0
2020-06-19T07:11:37.233Z
@0scar I am aware of the part cooling but it already sits at a 100 %. I think I will do an upgrade shortly. I have already done a temperature tower, bridging and stringing tests. The benchy was just to see everything together. How did you determine, the bed being to far away from the nozzle?
mrei
CC BY-SA 4.0
2020-06-19T08:01:20.950Z
If the fan is already at 100 %, then you print too hot or the cooling fan doesn't provide enough flow, many print fan ducts constrict airflow, we cannot see what you are using. Your first layer doesn't look that well, there are many channels, but it is hard to tell from the photo. Sometimes 200 °C is just too hot, most PLA can be printed from 185 °C. The last photo looks as if the nozzle has overpressure at the end of the outer wall or oozed out filament at the start of the outer wall.This could be a retraction issue.
0scar
CC BY-SA 4.0
2020-06-19T10:47:38.420Z
Thanks for the help so far. I'm going to play around with the retraction again and see if that helps.
mrei
CC BY-SA 4.0
2020-06-19T13:25:34.273Z
Over the course of a few testprints I increased the retraction distance and speed. Unfortunately the outcome is exactly the same. Could the printer feed to much filament or would I notice that otherwise? Are there other retraction parameters that could cause this issue?
mrei
CC BY-SA 4.0
2020-06-19T16:21:50.637Z
Nice results (not pretty, but helpful). Please try slowing down your non-printing moves to the same speed as your printing moves, and let us know if this helps. ;)
Davo
CC BY-SA 4.0
2020-06-20T10:02:06.710Z
Unfortunately reducing the travel speed didn't change anything.
mrei
CC BY-SA 4.0
2020-09-02T22:39:31.320Z
You might be overextruding a bit, causing some extra ooze when the nozzle stops for a layer change.
Adam Selker
CC BY-SA 4.0
2020-09-03T10:26:59.003Z
@mrei The heater block should probably have some thermal insulation on it. See if you can find a silicone insulator made to fit it, otherwise: [Efficient and easy way to thermally insulate the heat block of the hotend?](https://3dprinting.stackexchange.com/q/1247/11255)
Andrew Morton
CC BY-SA 4.0
2020-09-03T13:16:10.687Z
I agree with Andrew, that heater block gets cooled by the part cooling fan, which has an awkward position. Otherwise, I see that all the errors are at the start of the lines, and there is some underextrusion around it, hinting that you have to tweak your retraction distance.
Trish
<print-quality><pla><troubleshooting><anycubic-i3-mega>
Bumps in outer wall
mrei
# Bumps in outer wall

(Asked by: username_0 on 2020-06-18)

First of all, I'm quite new to 3D printing. After printing some temperature towers, stringing and bridging tests, I wanted to print the Bechys to see everything working together. I'm getting some strange "bumps" in the outer walls. It looks like for 2-3 layers, the filament gets lifted up.

[![infill before walls set](https://i.sstatic.net/l0w83.jpg)](https://i.sstatic.net/l0w83.jpg)

[![infill before walls unset](https://i.sstatic.net/VNmNB.jpg)](https://i.sstatic.net/VNmNB.jpg)

I first thought, the infill is printed too far in the outer shell, so I unchecked "Infill Before Walls" in Cura. Surprisingly the outcome did not change and the "bumps" where in the exact same spots as before.

I am aware of a part cooling problem, but my stock cooler already sits at 100 %. I don't think, the extruder temperature is too hot, with it being only 200 °C. As you can see, the printer only has a one sided cooling solution with a very small fan conduct.

[![fan conduct](https://i.sstatic.net/bOANt.jpg)](https://i.sstatic.net/bOANt.jpg)

Print settings:

* Printer: Anycubic I3 Mega S
* Slicer: Cura
* Material: PLA
* Extruder Temp: 200 °C
* Bed Temp: 60 °C
* Print speed: 45 mm/s
* Travel speed: 100mm/s
* Layer height: 0.2 mm
* Layer width: 0.4 mm
* Nozzle: 0.4 mm
* Infill: 10 %
* Retraction distance: 4.5 mm  
  Retraction speed: 40 mm/s

So I am suspecting it must have something to do with the way, it is sliced. Does anyone have an idea?

Update:
I started the print again with aligned seams. Now you can clearly see the artifact. At the point of the seam the print is warped inwards and upwards.

[![aligned seams](https://i.sstatic.net/TK9IT.jpg)](https://i.sstatic.net/TK9IT.jpg)

I did some more prints and tried to increase retraction distance up to 10 mm and retraction speed up to 60 mm/s, but I also did not manage to improve the print. I also tried to enable the "retract at layer change" option and to disable "Z Hop When Retracted" but without success.

I set the travel speed down to 45 mm/s with no change in print quality.

**Tags:** print-quality, pla, troubleshooting, anycubic-i3-mega
> **Comments:**
> **username_1**: Please slice with layer change aligned and post an image (20 layers should suffice), so that we can see if this is related to layer changes or not.  
> **username_2**: Hi welcome to 3DPrinting.SE! What can be seen on the bottom photo is that your nozzle is a little too far from the bed, and you aren't using enough part cooling (see the overhanging bow).  
> **username_0**: @0scar I am aware of the part cooling but it already sits at a 100 %. I think I will do an upgrade shortly. I have already done a temperature tower, bridging and stringing tests. The benchy was just to see everything together. How did you determine, the bed being to far away from the nozzle?  
> **username_2**: If the fan is already at 100 %, then you print too hot or the cooling fan doesn't provide enough flow, many print fan ducts constrict airflow, we cannot see what you are using. Your first layer doesn't look that well, there are many channels, but it is hard to tell from the photo. Sometimes 200 °C is just too hot, most PLA can be printed from 185 °C. The last photo looks as if the nozzle has overpressure at the end of the outer wall or oozed out filament at the start of the outer wall.This could be a retraction issue.  
> **username_0**: Thanks for the help so far. I'm going to play around with the retraction again and see if that helps.  
> **username_0**: Over the course of a few testprints I increased the retraction distance and speed. Unfortunately the outcome is exactly the same. Could the printer feed to much filament or would I notice that otherwise? Are there other retraction parameters that could cause this issue?  
> **username_1**: Nice results (not pretty, but helpful). Please try slowing down your non-printing moves to the same speed as your printing moves, and let us know if this helps. ;)  
> **username_0**: Unfortunately reducing the travel speed didn't change anything.  
> **username_3**: You might be overextruding a bit, causing some extra ooze when the nozzle stops for a layer change.  
> **username_4**: @mrei The heater block should probably have some thermal insulation on it. See if you can find a silicone insulator made to fit it, otherwise: [Efficient and easy way to thermally insulate the heat block of the hotend?](https://3dprinting.stackexchange.com/q/1247/11255)  
> **username_5**: I agree with Andrew, that heater block gets cooled by the part cooling fan, which has an awkward position. Otherwise, I see that all the errors are at the start of the lines, and there is some underextrusion around it, hinting that you have to tweak your retraction distance.  

---

## 2 answers

### Answer by username_6 on 2020-10-14. Score: 2

There are a few issues that could cause this. Roughness in your z-axis lead screw as pointed out by @TheLamestUsername is a leading contender I would say. I'd also extended that answer to include checking the belts for your X and Y axes as well as making sure that the rods the gantry slide on are smooth since the fault appears to be in about the same X-Y location as well in the one image.

However, there are a few alternatives as well. Check/confirm that the material that you're using doesn't have a lot of absorbed moisture in it. This can cause little bits of steam to 'pop' when they're extruded causing some bubbles

Because of how the material is folding at the location in the "updated" image this looks to be an issue with the starting and stopping. All of the layer's problems appear to be happening when the gantry moves up to the next layer. Essentially more material is coming out of the nozzle there (I think) than is what should be. Confirming material diameter with some calipers can help if there's just an offset (not too unlikely I don't think).

If the diameters are dead on I'd suggest reducing the nozzle temperature by a few degrees. The sensors used to measure the temperature aren't usually all that accurate, though their precision is often pretty good. While you may have it set at 200C that might not be the actual temperature. Calibration of the thermal sensors can drift over time, so while it might have been good on the last roll it may have drifted slightly. Or the material might be of slightly different composition. Try lowering the nozzle temp by 2-5 degrees and see if that has any effect.

You may also have a retraction setting that can be modified. Pulling the material back ever so slightly when it finishes the one layer as it moves to the next could alos reduce some of the extra material that's coming out.


---

### Answer by username_7 on 2020-09-23. Score: 0

The fact that the bumps were in the same spots on multiple occasions points to z-axis problems. Turn your printer off and manually turn the z-axis all the way from bottom to top. If there are any tight spots, there is some *z-axis binding*. If there are no tight spots, skip to the last paragraph.

Try taking off the z-axis by removing the set screws (pictured below). Remember which side was pointing up for a later step.

[![enter image description here](https://i.sstatic.net/GnC4r.jpg)](https://i.sstatic.net/GnC4r.jpg)

Once you do that, clean the screw thoroughly with a brush, cloth, solution, or a combination of those. Put the screw back in the opposite way this time.

If you get no bumps, then it was indeed the z-axis

If the bumps are still there, try lowering your temperature some more(200 is still a little high compared to what I do for PLA), and [calibrate your e-steps](https://all3dp.com/2/extruder-calibration-6-easy-steps-2/) if you haven't already.


---

