Is this a slicing issue?

[pastorhealer 0]

Wonder if someone can tell me why I'm having print quality issues at corners?

I just finished printing a cab for a Switcher engine and was surprised that there were
flaws in the print.  As with any 3d print, we can have flaws, but I'm wondering if
these were produced by the slicing. 

The reason I think this might be the case is the flaws have patterns in them.  As the
rows go up, the print is exactly the same, flawed, but slightly offset from the previous
row.

 

You will note that the problems are around corners and breaks in the row.

Any ideas?

[pastorhealer 0]

I realized I'm probably not going to get an answer to this post because there are too many variables.  So I decided to dissect the G-Code produced by Cura.

When I look at the code one layer at a time, in areas of this model, I see inconsistencies in where my print nozzle will be during the print.  Another words,
if the layers are the same going up one layer at a time, printing the mirror of the last layer, why would the gcode change?
 

For example;

 

 

 

When I look at the vertical walls of this part, the have a wave in them.  But the wave has a pattern in it. 

When I look at the corners where windows in the cab were placed, the print quality dived.  But not all along the Z axis.  Only when there was
a transition in the way the previous layer had been laid down.

I guess where I don't get this is I should be seeing code that looks like a mirror, row by row when the print is the same going upwards.

Secondly, why do corners or changes in layer right angels or even small angles change the print quality unless it's the code...

Forgive me if I don't know what I'm talking about.  Just trying to get good parts produced.

 

[yellowshark 153]

I had a similar problem in my early days, I would not have known how to decode g-code back then, but yours is very random whereas as mine was consistent. I was printing architecture and every time I jumped across  a window the resumed printing would produce an effect like yours; with the smaller models normally right across the front face (4 windows) until it settled down on the side walls (no windows). The areas below/above the windows were perfect. I resolved it in the end by slowing the print speed - whether or not I also played with retraction settings I do not recall. 

[pastorhealer 0]

Thanks for your reply.  I'm going to play with this more after I get the current project I'm working on finished.  I think I will cut out the overlapping layers from the full g-code file and print them, making subtle changes. Then examine what the results are.

 

What bugs me about this problem is that the majority of the windows in the Locomotive cab face printed perfectly.  So I know that the translation from model to gcode works.  What I also know is the problem occurs when the layer changes going up.  There has to be a transition bug in the software.  What I don't know is why it fixes itself over time as the layers go up.

Hopefully someone in Cura is going to take this post seriously and look into what is not only causing it, but how to overcome it.

And Cura... if you're listening...  I LOVE YOU GUYS! 

 

[yellowshark 153]

Copying @SandervG will make sure it comes to the attention of the developers although someone is normally watching.

[Brulti 177]

I have absolutely no idea how to decode gcode, but the visual effect reminds me of what happens when there's some underextrusion. It creates very similar patterns.

[SandervG 1,521]

Hi! 
If you are interested in learning more about gcode commands, this is an interesting page to fall back on. If I look at your first snippets of the gcode it seems to deploy the X and Y layers at the same location, you can see the coordinates are the same. The E varies, and E indicate extrusion. I am not entirely sure, but I believe in corners the extrusion flow could vary a bit and it relates to acceleration and jerk. F1200 refers to the speed of the printhead. 

I think you are probably affected by suboptimal acceleration settings. Are you using the latest firmware / Cura, to have an idea what you are slicing with? (would you care to upgrade if you don't?)

 

[SandervG 1,521]

Also, I think this also touches @tinkergnome's excellent field of expertise. (And @nallath for:

11 hours ago, pastorhealer said:

And Cura... if you're listening...  I LOVE YOU GUYS! 

 

[pastorhealer 0]

I have since upgraded to 3.2, but I was using 3.1 during this print. 

I'm going to test snippets of the original gcode to see if it is repeatable and whether changing any settings makes a difference.  I'll let you know...  Thanks