Top thickness not respected when using adaptive layers

[mechamecha 64]

I've noticed that Cura doesn't respect the "top thickness" setting when adaptive layers are used. I haven't been able to test this extensively, but I've had a number of failed prints (brittle top surfaces with holes in them) if top layers are calculated to use very thin layers in the specified adaptive layers range.

[mechamecha 64]

In such cases, I've had to multiply my top thickness setting by 2 or 3 to get acceptable top surfaces.

[kmanstudios 1,120]

If your top layer gets the lowest value layer (Say 0.04 VS 0.4) it will need the multiplier because it is a much thinner layer. It will also depend on the percentage of infill and type.

[mechamecha 64]

24 minutes ago, kmanstudios said:

If your top layer gets the lowest value layer (Say 0.04 VS 0.4) it will need the multiplier because it is a much thinner layer. It will also depend on the percentage of infill and type.

 

Yes, that's pretty much what I said. But that's not the way it should be. Adaptive layers shouldn't be completely ignoring the top thickness setting.

[kmanstudios 1,120]

No, that is not what you said. And it cannot be both. Adaptive layers changes the thickness of the layer, ergo, you have to compensate. Cura is not magic, you do have to do some work ya know.

[cjs 34]

@mechamecha Do you set your top thickness as mm or as layer count? 

[kmanstudios 1,120]

23 minutes ago, cjs said:

@mechamecha Do you set your top thickness as mm or as layer count? 

Excellent question..... :)

[mechamecha 64]

7 hours ago, kmanstudios said:

Excellent question..... ?

 

C'mon, guys, give me some credit here... I set it by mm. If I set it by layers, I wouldn't be posting this.

[mechamecha 64]

9 hours ago, kmanstudios said:

No, that is not what you said. And it cannot be both. Adaptive layers changes the thickness of the layer, ergo, you have to compensate. Cura is not magic, you do have to do some work ya know.

 

If you take into consideration that I'm talking about setting the top thickness in mm, then, yes, that is pretty much what I said. For example, if I have my top thickness set to 1 mm and adaptive layers are calculated to use something like .07 mm for those layers, I need to double (at least) my top thickness setting (therefore, something like 2 mm) to get an acceptable top surface.

 

I'm not sure why anyone would set their top/bottom thickness in layers instead of mm...

Edited May 20, 2018 by mechamecha
Clarification

[kmanstudios 1,120]

34 minutes ago, mechamecha said:

 

C'mon, guys, give me some credit here... I set it by mm. If I set it by layers, I wouldn't be posting this.

How we do we know that? People come here all the time and do not state credentials or, in your case, provide full information of procedure. Why take it personal?

 

29 minutes ago, mechamecha said:

If you take into consideration that I'm talking about setting the top thickness in mm, then, yes, that is pretty much what I said.

Now that we know that, it does make a difference.

 

30 minutes ago, mechamecha said:

I'm not sure why anyone would set their top/bottom thickness in layers instead of mm

Specific count and not having to do math......people do things all the time that may not make sense to you or me or anybody but themselves. That is why a better reporting of methodology, specifics as well as screenshots help. We cannot read the forum poster's minds or intentions. That is why @cjs asked a most pertinent question as it solved a bit of the mystery of what you were stating.

[mechamecha 64]

I apologize if my replies came across as snippy. I'm not taking any of this personally; I just thought it was kind of funny. I probably should have clarified in my original post that I was merely reporting a bug and not necessarily asking for assistance.

 

But, seriously, if Cura was doing exactly what it was supposed to do (printing 5 top layers when 5 top layers were specified), I wouldn't have posted this. I know this forum receives posts from people with a wide range of 3D printing expertise, but we shouldn't just assume that everyone is new and confused.

 

I do appreciate both of you for taking the time to respond.

 

 

[mechamecha 64]

This isn't even a difficult bug to reproduce. All you need to do is take a cube, fillet the top surface, then slice it in Cura with adaptive layers turned on. If I slice the attached STL using .15 mm as the base layer height, 0.1 as the maximum variation, and top thickness set to 1 mm, there will be 7 top layers generated, and each layer will be approximately .05 mm thick. That results in a top surface that is approximately .35 mm thick, not anywhere close to the specified 1 mm.

adaptive_layers_bug.stl

Edited May 20, 2018 by mechamecha
Corrected decimal position in base layer height value

[mechamecha 64]

So Cura is apparently calculating the number of top (and probably bottom) layers relative to the base layer height, and not on the calculated adaptive layer heights.

[cjs 34]

Great that you spotted this "wrong" behaviour @mechamecha and also reported it with a guide to reproduce! 

I will link @ctbeke as he worked on the adaptive layer feature. Maybe it's an easy fix.

[mechamecha 64]

Thanks, @cjs!

[ctbeke 133]

We’re aware of this issue, but it’s not an easy fix. It comes down to Cura engine only receiving the amount of top/bottom layers and skin from the UI, not the absolute thickness in mm or something. To fix it, the way the setting are passed has to be changed, and also the algorithms that calculate the skins and top layers from those values. We’ll probably work on this first when we ever come around to improving adaptive layers. I’m currently not in the Cura team, so can’t give any details on further planning. 

[mechamecha 64]

Thank you for replying, @ctbeke!

[yellowshark 153]

19 hours ago, mechamecha said:

>>snip

 

I'm not sure why anyone would set their top/bottom thickness in layers instead of mm...

Lol I do neither/ both. I decide how many layers I want and then convert that to mm. No I cannot defend that or promote it; it is a bit like eating Weetabix for breakfast, although I can defend that ?

[Adam324 13]

Thank you for this thread.  I have been going crazy trying to find out why my top layers have been getting holes in them when they worked fine on the same stl files a month ago.  In coincided with using adaptive layers.  I do specify my layers in mm.

Edited May 25, 2018 by Adam324

[Adam324 13]

To add to this.  I realized that on a print that has top layers at different heights, some of the top layers were ok and others were not.  It turns out that some top layers were at near maximum layer thickness and others were at the minimum layer thickness.  You can compensate by adding more mm to the top layer height setting (double or 4 times as much) but then your thicker layers would take up 4 times as much filament... not just the thin layers.  That could add up to a lot of extra filament depending on the object.

Edited May 25, 2018 by Adam324

[mechamecha 64]

Exactly right, that's why it would be really nice if they're able to fix this bug very soon.

[AbeFM 35]

I think I mentioned this some months back - that the top thickness, set by mm, should be respected.

 

In general, the variable layer heights takes a poor approach - we'd be much better served with an AVERAGE layer height.

 

Every print you either decide not to care, or tweak the numbers again and again and again until you kinda get the behavior that:

 

Respecting TOP and BOTTOM thickness

Enforcing an AVERAGE layer height

 

Those two changes could make the feature a LOT more user friendly and produce better results. It's been beating a dead horse for me, I hope you have more luck with it.

[mechamecha 64]

I'm currently trying Slic3r's variable layers to see if it does a better job for me. It's not automated, but so far I like the way it allows you to "paint" on where you want the thinnest and thickest layers to be instead of forcing you to have variable layers for every single detail in your print.

[UbuntuBirdy 56]

Does anyone know if there will soon be a solution to this problem? Would be really great, because in my opinion adaptive layers are one of the most important opportunities in slicing.

[AbeFM 35]

+1

 

I guess no action for a month followed by more talk and then redoubled efforts of no dev participation labels it a "just live with it" topic.

 

In the meantime, you could try taking the top thickness you want, dividing it manually by the layer height, and changing the number. 😛

 

 

More seriously - is there something the Devs need to move forward on this? Is it "not an issue", a user error, or is there some benefit to parts missing their tops that we just don't see? If you're just busy, could you engage us just enough to let us know?