Wrong Slicing ! A critical bug of Cura 4.8?

[blackgun 0]

Hi guys

I was excited to upgrade to Cura 4.8.0 but so frustrated by the supporting issues. 

It slicing algorithm seems has a serious bug, getting a wrong result. I didn't notice that, and realized it after a 10 hours printing work. 

I couldn't believe how it's released with such serious problems. I have 3 printers , printing for 5 years, this is my first time of such experience.

I was printing with Tree support, but Normal type support has same issue.

My env: MacOS v11.1 Big Sur, Macbook Air M1, Cura 4.8.0. 

 

 

 

 

Edited December 20, 2020 by blackgun

[GregValiant 1,251]

What exactly is your wrong result?

 

Support Density = 1% and Support Line Distance = 120mm.  That is very, very sparse support.  Almost none.

 

Are features missing as well?  Since they don't appear in the preview they are either too fine to print (doubtful with a 0.3 nozzle) or is it possible there is a flaw in the model?

[blackgun 0]

There's no problem with the support, I hided them in the screenshots.  

The problem is Cura slicing changed the model.

 

[ahoeben 1,948]

I'm sorry you lost 10 hours worth of printing. Always check the preview before starting a big print.

 

There could be a problem with the model that affects how it is sliced. There are also many settings that affect the slicing.

 

Please save and share a project, so we can see the model and the settings you used to slice it. Then we can see if it is indeed a problem with Cura, your model or your settings.

[blackgun 0]

OK. All objects have the model changed issues, I saved one of the objects in the attached project file. 

The models slicing works well with Cura 4.6.1 on another computer. 

AI3M_HS_B.3mf

[stan_bulgaria 4]

Hello Blackgun,

 

I'm using Creality Ender 3 V2 on OpenSUSE Leap 15.2 with Cura 4.8.0. 

 

I opened your project and sliced it as it is, so it has only 2 hours and 23 min estimated printing. But it is missing the hole in the bottom. However all the rest is present.

 

I turned the detail to lay on one side. It has the holes that were missing but now the hole that appears on the bottom is missing.

 

So the issue may be connected with the initial layers.

 

I switched off the infill colors to see better the inprints/holes.

[GregValiant 1,251]

Using Cura 4.8.0

With the part vertical and the Anycubic Mega X the active printer I got the same results as you - no slots.  So I switched to my Ender3Pro and the slots showed up.  All features are there.  Nozzle was .4 and the layer height was .2.

 

So it isn't Cura.  That leaves your printer definition and/or the material profile.

 

I reloaded the 3mf file and with the Anycubic active selected "Generic PLA" and when prompted I hit "Discard Settings".  The slots and all other features showed up.  I then re-selected Generic PETG and re-sliced and everything was good.  All the model features were there.

There is something in your printer settings that is interfering with the material settings or vice-versa.  I made some changes to the Cura print settings and saved this 3mf file.  Take a look.  You will probably want to make further changes.  If the slots disappear again you will have found the setting that is causing the interference.

 

 

 

Rev_AI3M_HS_B.3mf

[blackgun 0]

@stan_bulgaria, that's also what happened to me, changing the object placement in any direction will still have the model changed, like filling the hole feature or adding some pyramid at the bottom side. 

 

@GregValiant, that's a solution, it's solved by switching the filament general PETG->PLA->PETG. Many thanks. But I don't think the printer setting or filament setting should change the model or modify the feature, that's definitely a software bug. 

 

[GregValiant 1,251]

It could be.  I just use the program.  The thing is that the printer settings are submitted by other printer manufacturers or (as in the case of Creality) by users of the printers.  I would think that Ultimaker checks them a bit but they don't go out and buy other manufacturers printers and build other peoples software for them.  "Open Source" does not imply "Non-Profit".  Ultimaker sells their own printers.

Regarding the material settings I would think that they come from a manufacturers recommendations.  Does Ultimaker have a laboratory where they test other manufacturers products?  It would seem unlikely.

Cura is not bug free but from all of the posts here and there on the web in the year I've been hanging around these sites, there aren't a lot of bugs.  This problem may indeed be a bug in Cura but it involves a third party description of their printers capabilities and a fourth party description of what their filament requires.

[ahoeben 1,948]

12 hours ago, blackgun said:

All objects have the model changed issues, I saved one of the objects in the attached project file.

 

In the project you shared, the "Make overhang printable" setting is turned on. Turn it off, and the model will sliced as expected. Cura did nothing wrong, it did as you instructed it to do.

 

Out of shear interest, why did you turn it on in the first place? The past few weeks I have seen at least 3 people complaining that Cura was not slicing right because they had this setting turned on. Was it featured in some tutorial? The setting has its uses, but it is not supposed to be turned on for all models. It will add extra geometry to the model and it can easily fill up bottom-facing holes.

[GregValiant 1,251]

Aaah Haaa.  And that is why discarding the settings worked.  The PETG went back to default and "Make Over Hang Printable" was turned off.  I had played with settings for an hour and missed it.

I tell ya, if I knew what I was doing I'd be dangerous.  Once again I fumble around, come up with a fix that works but it's for the wrong reason.  Thank you @ahoeben.  My knowledge of things Cura goes up another notch.

[nallath 1,120]

7 hours ago, ahoeben said:

 

The past few weeks I have seen at least 3 people complaining that Cura was not slicing right because they had this setting turned on.

We are seriously considering renaming it to "Force Overhangs Prinable" or something. Make printable sounds like something you'd always want (whereas it's clearly not what you'd want. To be honest; I don't think that this is something people should enable at all!)

[blackgun 0]

@ahoeben @nallath Oh good, it's a feature instead of a bug 😵 (I haven't seen its benefit, maybe move it to the add-on plugin if it's only useful for very few users) I thought I never touched that setting, I don't know why it's checked. If you found many people has such strange situation, it couldn't be an accident or misunderstanding from my software product experience.   It might be caused by some bug, think about why changing filament (PETG->PLA->PETG) can solve it, that might be a clue. 

 

Another minor bug is sometimes (30% chance) the object models are not movable/controllable, restart the app will solve it.  (Env: MacOS v11.1 Big Sur, Macbook Air M1, Cura 4.8.0. )

 

 

[stan_bulgaria 4]

On 12/22/2020 at 5:54 PM, nallath said:

We are seriously considering renaming it to "Force Overhangs Prinable" or something. Make printable sounds like something you'd always want (whereas it's clearly not what you'd want. To be honest; I don't think that this is something people should enable at all!)

I looked in the settings of my print settings. I have made  visible "Make Overhang Printable", but it is not switched on. The description when the cursor is over it is clear.

[ahoeben 1,948]

On 12/22/2020 at 4:54 PM, nallath said:

We are seriously considering renaming it to "Force Overhangs Prinable" or something

Something along the line of "Remove overhanging features" might better indicate that the model is being modified.