<p>I ultimately concluded that the material isn't great. I printed this part with multiple other PLAs and never observed any problem. The Polyalchemy PLA looks great, but for any part that has some sort of mechanical constraint, it behaves poorly.</p>

CC BY-SA 4.0
2021-08-27T09:52:41.340Z
2021-08-27T09:52:41.340Z
JPFrancoia
<p>I am looking at your picture, and I realize that it is not only that the perimeter is detaching from the infill, but also that the perimeter is breaking.</p>
<p>Once the perimeter breaks, the weaker connection with the infill will surely break, too.</p>
<p>You could try:</p>
<ol>
<li>Using more than two perimeter layers.  Go big. Try five.</li>
<li>Add a fillet where the ring attaches so that the force is not focused on a point.</li>
<li>Choose an infill percentage and pattern that maximizes the contact between the perimeter and the body.</li>
<li>Change the angle on the bed at which the keychain is printed so that the infill maximally connects with the breaking point.  That might make the ring be 45 degrees off the X and Y axes.</li>
</ol>

CC BY-SA 4.0
2021-08-24T16:17:21.017Z
If the perimeter breaks, it's likely at a seam that didn't fully bond due to a retraction problem just before the wall was started, where the start of the wall was underextruded or missing entirely. Note that slicer settings usually prefer making the seam at the sharpest concave corner, which matches where the break in the picture was.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-08-24T19:41:20.393Z
@r.. then may I assume that you would recommend turning on random seams, if the slicer supports it?  Perhaps also changing the retraction settings?
cmm
CC BY-SA 4.0
2021-08-24T20:18:37.937Z
No, diagnosing and fixing the retraction settings or whatever it is causing the weak seam. Random seams just come out really ugly and aren't even reproducible, which is bad for getting parts you can test and improve.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-08-24T13:35:31.510Z
2021-08-24T13:35:31.510Z
cmm
<p>I'm printing with a Prusa MK3, with the following settings:</p>

<ul>
<li>3 perimeters</li>
<li>50&nbsp;% infill</li>
<li>infill overlap: 50&nbsp;%</li>
</ul>

<p>The filament is Polyalchemy emerald green (PLA). Nozzle temperature: 210&nbsp;°C.</p>

<p>On a simple part (it's a keychain), the shell detaches if I apply a bit of force on a zone of the part that is "fragile". See picture. You might not be able to see it, but only the 2 external perimeters detach from the rest of the part. I used to print this part on another printer, and I never observed this problem.</p>

<p>Any idea on how to solve this problem? It seems the 3 external perimeters didn't fuse properly.</p>

<p><a href="https://i.sstatic.net/cUI0O.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cUI0O.jpg" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-12-14T19:07:44.413Z
What is the printing speed? You are probably printing too fast. I've seen this happening a lot with PETG.
0scar
CC BY-SA 4.0
2019-12-14T19:22:53.503Z
Not particularly high, 45 mm/s for the internal perimeters, 25 for the external ones. Infill 80.
JPFrancoia
CC BY-SA 4.0
2019-12-14T21:13:28.257Z
Nope, it's not the speed: I reduced by 50% the speeds above and got the same results, the part is brittle at the same place.
JPFrancoia
CC BY-SA 4.0
2019-12-14T22:48:57.310Z
Belts tight? Under extruding?
0scar
CC BY-SA 4.0
2019-12-16T00:19:06.663Z
What slicer? Any weird setting?
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2019-12-16T17:58:15.730Z
The overlap between infill and perimeters may be too low. Or there is underextrusion. I would try 3% higher extrusion rate.
FarO
CC BY-SA 4.0
2019-12-16T23:00:05.060Z
210 is quite hot for PLA, you might try to tone it down to 200 or such. How many top layers do you use? I use 4 to 6 on a mere 9% infill and get quite sturdy parts (with 2-3 shells).
Trish
CC BY-SA 4.0
2019-12-18T23:11:07.943Z
Did you calibrate your e-steps? what are your nozzle size and line/wall width settings?
Quad
CC BY-SA 4.0
2019-12-18T23:47:08.243Z
I think the problem is underextrusion. I normally use Slic3r by Prusa. I tried the same print today, sliced with Cura: same fragility of the piece. I then tried with ABS, sliced with Slic3r: no problem. I then tried again with the green PLA from polyalchemy, with 1.1 extrusion factor: still failing. At 1.3 extrusion factor, the part is as solid as I would expect (I should also have tried with another PLA for a proper control...). I think I just need to dial in the extrusion for this filament. The sweet spot is between 1.1 and 1.3 (which seems a bit high, but ok).
JPFrancoia
<prusa-i3><pla>
Shell detaches from the rest of the part
JPFrancoia
# Shell detaches from the rest of the part

(Asked by: username_0 on 2019-12-14)

I'm printing with a Prusa MK3, with the following settings:

* 3 perimeters
* 50 % infill
* infill overlap: 50 %

The filament is Polyalchemy emerald green (PLA). Nozzle temperature: 210 °C.

On a simple part (it's a keychain), the shell detaches if I apply a bit of force on a zone of the part that is "fragile". See picture. You might not be able to see it, but only the 2 external perimeters detach from the rest of the part. I used to print this part on another printer, and I never observed this problem.

Any idea on how to solve this problem? It seems the 3 external perimeters didn't fuse properly.

[![enter image description here](https://i.sstatic.net/cUI0O.jpg)](https://i.sstatic.net/cUI0O.jpg)

**Tags:** prusa-i3, pla

> **Comments:**
> **username_1**: What is the printing speed? You are probably printing too fast. I've seen this happening a lot with PETG.  
> **username_0**: Not particularly high, 45 mm/s for the internal perimeters, 25 for the external ones. Infill 80.  
> **username_0**: Nope, it's not the speed: I reduced by 50% the speeds above and got the same results, the part is brittle at the same place.  
> **username_1**: Belts tight? Under extruding?  
> **username_2**: What slicer? Any weird setting?  
> **username_3**: The overlap between infill and perimeters may be too low. Or there is underextrusion. I would try 3% higher extrusion rate.  
> **username_4**: 210 is quite hot for PLA, you might try to tone it down to 200 or such. How many top layers do you use? I use 4 to 6 on a mere 9% infill and get quite sturdy parts (with 2-3 shells).  
> **username_5**: Did you calibrate your e-steps? what are your nozzle size and line/wall width settings?  
> **username_0**: I think the problem is underextrusion. I normally use Slic3r by Prusa. I tried the same print today, sliced with Cura: same fragility of the piece. I then tried with ABS, sliced with Slic3r: no problem. I then tried again with the green PLA from polyalchemy, with 1.1 extrusion factor: still failing. At 1.3 extrusion factor, the part is as solid as I would expect (I should also have tried with another PLA for a proper control...). I think I just need to dial in the extrusion for this filament. The sweet spot is between 1.1 and 1.3 (which seems a bit high, but ok).  

---

## 2 answers

### Answer by username_0 on 2021-08-27. Score: 1 | Accepted answer

I ultimately concluded that the material isn't great. I printed this part with multiple other PLAs and never observed any problem. The Polyalchemy PLA looks great, but for any part that has some sort of mechanical constraint, it behaves poorly.


---

### Answer by username_6 on 2021-08-24. Score: 0

I am looking at your picture, and I realize that it is not only that the perimeter is detaching from the infill, but also that the perimeter is breaking.

Once the perimeter breaks, the weaker connection with the infill will surely break, too.

You could try:

1. Using more than two perimeter layers. Go big. Try five.
2. Add a fillet where the ring attaches so that the force is not focused on a point.
3. Choose an infill percentage and pattern that maximizes the contact between the perimeter and the body.
4. Change the angle on the bed at which the keychain is printed so that the infill maximally connects with the breaking point. That might make the ring be 45 degrees off the X and Y axes.

> **Comments:**
> **username_2**: If the perimeter breaks, it's likely at a seam that didn't fully bond due to a retraction problem just before the wall was started, where the start of the wall was underextruded or missing entirely. Note that slicer settings usually prefer making the seam at the sharpest concave corner, which matches where the break in the picture was.  
> **username_6**: @r.. then may I assume that you would recommend turning on random seams, if the slicer supports it?  Perhaps also changing the retraction settings?  
> **username_2**: No, diagnosing and fixing the retraction settings or whatever it is causing the weak seam. Random seams just come out really ugly and aren't even reproducible, which is bad for getting parts you can test and improve.  

---

