<p>While doing the setup of a new machine I printed a small retraction test which showed that layers at different heights present a varying section. The whole area of the layer is expanding and contracting similarly in both the x and y directions and simultaneously in both the towers.</p>
<p><a href="https://i.sstatic.net/O9GPB.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/O9GPB.jpg" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/NVwk2.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/NVwk2.jpg" alt="enter image description here" /></a></p>
<p>The layer area is very small and <strong>I did not see the same effect printing larger parts</strong>.</p>
<p>The printer has a long bowden tube, and that may be a source of a number of weird behaviors. But what I like to think is a squish resonance: let's say that for any reason (even a mechanical one) the height of a layer is slightly larger, the deposed material will not get squished out as far as for the previous layer, resulting in a slightly taller layer but with smaller cross section. Depending on how the situation evolves, we may hit the opposite case few layers later, with the top of the print that has raised close to the nozzle so the layers now are getting squished more.</p>
<p>I could do several more tests with other temperatures, different filaments... but it is quite a corner case, so I do not really need to invest a bunch of time studying it, still I would like to get a better understanding of the phenomenon.</p>

CC BY-SA 4.0
2021-08-06T12:17:17.260Z
Do you have some reason to believe in inconsistent material flow or inconsistent Z positioning?
Davo
CC BY-SA 4.0
2021-08-06T16:16:24.277Z
If you're printing that object by itself, that is a difficult print due to lack of time to cool.  Have you tried printing multiples of the same object in a single print?
Perry Webb
CC BY-SA 4.0
2021-08-08T02:37:22.697Z
It may be informative to see if the issue is still seen with all forms of retraction disabled.  Or if available for your printer a test of the same print with stock default slicer settings.
Kezat
CC BY-SA 4.0
2021-08-08T02:40:13.503Z
If this is a standard off the shelf printer, information as to the model of printer might be helpful. Along with the slicer used.
Kezat
CC BY-SA 4.0
2021-08-11T16:53:13.397Z
Out of curiosity, Is your bed heated? Can you test the print with the heated bed off and report the results?
craftxbox
CC BY-SA 4.0
2021-08-12T06:19:29.027Z
@craftxbox the bed was heated very slightly to 40 C. It is a very large bed 500x500 mm and I was printing in a corner on the top of a supporting screw, which is not directly heated. I will see if I can get some time to do further experiments, but, as stated in the question, that is very low priority now.
DarioP
CC BY-SA 4.0
2021-08-12T11:29:45.767Z
Ah okay, yeah, disregard the test then. Had a thought it might be to do with PID fluctuations causing the Z height to vary, usually only manifests in minor banding on parts but since the part is so small I thought it mightve manifested in a larger problem.
craftxbox
<fdm><bowden><layer-height>
Weird layer cross section resonances
DarioP
# Weird layer cross section resonances

(Asked by: username_0 on 2021-08-06)

While doing the setup of a new machine I printed a small retraction test which showed that layers at different heights present a varying section. The whole area of the layer is expanding and contracting similarly in both the x and y directions and simultaneously in both the towers.

[![enter image description here](https://i.sstatic.net/O9GPB.jpg)](https://i.sstatic.net/O9GPB.jpg)

[![enter image description here](https://i.sstatic.net/NVwk2.jpg)](https://i.sstatic.net/NVwk2.jpg)

The layer area is very small and **I did not see the same effect printing larger parts**.

The printer has a long bowden tube, and that may be a source of a number of weird behaviors. But what I like to think is a squish resonance: let's say that for any reason (even a mechanical one) the height of a layer is slightly larger, the deposed material will not get squished out as far as for the previous layer, resulting in a slightly taller layer but with smaller cross section. Depending on how the situation evolves, we may hit the opposite case few layers later, with the top of the print that has raised close to the nozzle so the layers now are getting squished more.

I could do several more tests with other temperatures, different filaments... but it is quite a corner case, so I do not really need to invest a bunch of time studying it, still I would like to get a better understanding of the phenomenon.

**Tags:** fdm, bowden, layer-height

> **Comments:**
> **username_1**: Do you have some reason to believe in inconsistent material flow or inconsistent Z positioning?  
> **username_2**: If you're printing that object by itself, that is a difficult print due to lack of time to cool.  Have you tried printing multiples of the same object in a single print?  
> **username_3**: It may be informative to see if the issue is still seen with all forms of retraction disabled.  Or if available for your printer a test of the same print with stock default slicer settings.  
> **username_3**: If this is a standard off the shelf printer, information as to the model of printer might be helpful. Along with the slicer used.  
> **username_4**: Out of curiosity, Is your bed heated? Can you test the print with the heated bed off and report the results?  
> **username_0**: @username_4 the bed was heated very slightly to 40 C. It is a very large bed 500x500 mm and I was printing in a corner on the top of a supporting screw, which is not directly heated. I will see if I can get some time to do further experiments, but, as stated in the question, that is very low priority now.  
> **username_4**: Ah okay, yeah, disregard the test then. Had a thought it might be to do with PID fluctuations causing the Z height to vary, usually only manifests in minor banding on parts but since the part is so small I thought it mightve manifested in a larger problem.  

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## 0 answers

