The Arachne perimeter generator does not adhere to the geometry of objects?

[2go 6]

Hello! I've created a small slanted circular object to illustrate the issue. The project file is attached.

 

To minimize variables, I am using the default profile (UM2+ / PLA) that Cura ships with.

 

In the first screenshot, you can see surface irregularities where the object becomes thin enough to be printed only using skin lines, where the infill no longer fits. Another 'band' is noticeable where the perimeter generator switches to a single line of deposited filament.

 

 

If I export the G-code and load it back into Cura, the issue becomes much more pronounced.

 

 

When I print the file, the actual result in terms of wall smoothness is somewhere in between these two screenshots. I can definitely feel these 'bands' or 'ridges' with my finger.

 

I would greatly appreciate any insight into this. Both the STL and project files are attached. Thank you.

 

 

test.stl UM2_test.3mf

[Slashee_the_Cow 269]

The relevant settings I can think of for this are:

Walls > Wall Transitioning Filter Margin: Changes how much thinner/thicker than usual walls can before it will add (or remove) more walls, and

Walls > Minimum Wall Line Width: What it says on the box: the thinner your lines, the higher resolution you get when it comes to reducing them. Just be aware you're limited by your nozzle size on this, the general guideline is don't go below 60% of your nozzle diameter.

 

You may be able to use a combination of those to get a less noticeable transition (maybe set the margin to half the minimum width? I haven't tried), but unfortunately this is just one of the realities of FDM 3D printing that you can't really avoid.

 

It will also be affected by Experimental > Slicing Tolerance but that would likely only change where the transitions are.

Edited February 22 by Slashee_the_Cow

[2go 6]

Thank you @Slashee_the_Cow for your input. Unfortunately, using all of these settings, either on their own or in combination with one another, did not lead to a solution. As you correctly predicted, I was only able to adjust the problematic area up or down along the model.

 

I prepare hundreds of small models like these for printing every week and have been searching for a solution to this problem ever since the Arachne was released, so it's been almost 2 years now. I've tried all major slicers on the market, and they all seem to have issues with printing thin lines. However, the situation is definitely better than it was pre-Arachne.

 

Anyway, I just hope that in a year or two, a new Cura release will magically solve this 😄  While waiting for that, I wonder if anyone would have an idea of how to somewhat adjust the slicing behavior so that the inside wall would be smoother, even at the expense of the outer wall? Essentially, 'align' the walls at the problematic area to the inside of the model so that it is smooth there, while the outside wall becomes even more rough. I wouldn't really mind that.

[Dustin 130]

1 hour ago, 2go said:

Thank you @Slashee_the_Cow for your input. Unfortunately, using all of these settings, either on their own or in combination with one another, did not lead to a solution. As you correctly predicted, I was only able to adjust the problematic area up or down along the model.

 

I prepare hundreds of small models like these for printing every week and have been searching for a solution to this problem ever since the Arachne was released, so it's been almost 2 years now. I've tried all major slicers on the market, and they all seem to have issues with printing thin lines. However, the situation is definitely better than it was pre-Arachne.

 

Anyway, I just hope that in a year or two, a new Cura release will magically solve this 😄  While waiting for that, I wonder if anyone would have an idea of how to somewhat adjust the slicing behavior so that the inside wall would be smoother, even at the expense of the outer wall? Essentially, 'align' the walls at the problematic area to the inside of the model so that it is smooth there, while the outside wall becomes even more rough. I wouldn't really mind that.

Can you please report this as a bug on github to ensure it is properly brought to the attention of the Dev Team.
https://github.com/Ultimaker/Cura/issues

[2go 6]

Thank you, I have reported it on GitHub.

 

Also, I realize that my reply and additional question yesterday might have sounded a bit convoluted, so here is a visual aid. Currently, Cura slices this file similarly to the image on the left.

 

I wonder if there is a combination of settings that would force it to slice more like the picture on the right, preserving the geometry of the 'inner' wall at the expense of the 'outer' one.

 

[Slashee_the_Cow 269]

1 hour ago, 2go said:

I wonder if there is a combination of settings that would force it to slice more like the picture on the right, preserving the geometry of the 'inner' wall at the expense of the 'outer' one.

The way you designed your model, it does exactly that: you have a flat inner wall and the outer wall slopes inwards. Here's what it looks like going through layer view from above with an orthographic projection:

<tries to upload GIF, fails>

Okay, the video in the zip file I attached to this will show you that as you scroll through the layers, the inner wall remains constant.

cura inner wall preserve.zip

[2go 6]

@Slashee_the_Cow Thank you for taking the time to record the video. Yes, it does look just fine from the top-down view, slightly zoomed out.

 

However, to replicate the issue, all I need to do is slice the project, export G-code, load the G-code back into Cura, and zoom in to the problematic area. I have attached a screenshot.

Both the inner and outer skin walls are offset inside by a small amount. It also prints this way, so it's not just a display issue. 

 

P.S. It looks better when I slice the project file; however, the actual printed result is more similar to the one I get by loading the exported G-code back into Cura. You can see the difference in the screenshots in the first post of this thread.

 

[2go 6]

P.P.S. <Tries to record a video, fails.> Here is a zoomed-in screenshot, an orthographic view. This represents one of the top layers, printed in a single line, not aligned with where an inner wall should be.

 

[Slashee_the_Cow 269]

Fair enough - the 3mf file you uploaded in your first post only contains the model (try setting up everything and slicing it, then save the project) so I can't see your settings.

 

About the only things I can think of off the top of my head (and it slightly mitigates, not fixes the problem) is to use the thinnest lines possible (for all lines, not just set the minimum) - on a 0.4mm nozzle I usually set 0.26mm as the minimum, but the "general rule" for line width is between 60-150% of your nozzle size.

And I've never tried this one myself (so you should at least look at the gcode to test it) but Walls > Outer Wall Inset. You wouldn't want it very high (as in start at like 0.1mm) but it's designed to get the outer walls to overlap the inner walls instead of the model, so might come in handy. Or might ruin everything. That's why you test in either small scale or viewing the gcode, not printing it full size every time you make a minor change.

[2go 6]

On 2/27/2024 at 12:02 PM, Slashee_the_Cow said:

Fair enough - the 3mf file you uploaded in your first post only contains the model (try setting up everything and slicing it, then save the project) so I can't see your settings.

 

Oh, I was not aware of it. Anyway, as I mentioned originally, it is just a default UM2+ profile 'Normal' that ships with Cura. That's on purpose, so as not to introduce new variables, since my printing profiles are heavily modified.

 

On 2/27/2024 at 12:02 PM, Slashee_the_Cow said:

About the only things I can think of off the top of my head (and it slightly mitigates, not fixes the problem) is to use the thinnest lines possible (for all lines, not just set the minimum) - on a 0.4mm nozzle I usually set 0.26mm as the minimum, but the "general rule" for line width is between 60-150% of your nozzle size.

And I've never tried this one myself (so you should at least look at the gcode to test it) but Walls > Outer Wall Inset. You wouldn't want it very high (as in start at like 0.1mm) but it's designed to get the outer walls to overlap the inner walls instead of the model, so might come in handy. Or might ruin everything. That's why you test in either small scale or viewing the gcode, not printing it full size every time you make a minor change.

 

As I mentioned previously, I have been trying to crack this for almost two years, printing models like this in the thousands every month. I will make sure to post a solution if I find one, in case anyone Googles this thread in the future. I will try offsetting walls at a specific height using the 'cutting edge' modifier next, so it affects only specific layers. It's convoluted and unnecessarily complicated, but it might work.

[Slashee_the_Cow 269]

You could try manually editing the gcode, which isn't something I'd normally suggest. If you use the "Arc Welder" plugin from the ever awesome @ahoeben it will convert circles from a long bunch of linear moves to a few arc moves. You can then find a layer with the circle you want, then copy its moves (excluding the height, but Cura usually changes height in a separate move anyway, and the extrusion rate, but that's usually a simple G1 F<number> E<number> and if you're using arc moves those are G2 and G3 anyways) to the upper layers.

 

Difficult? Depends on how much time you've spent playing with gcode. If you know what you're looking for and where to find it, not too hard. Fiddly? Heck yes. I can't guarantee it would work but sometimes you have to get your hands dirty instead of leaving your fate in the hands of the computers.

 

(I guess you could try it without using Arc Welder, but it'd be a lot more hassle)

[ahoeben 1,950]

Note that in order for ArcWelder to work, your printer firmware has to properly support arc movements. Not all firmware versions do.