Z offset between supports and object wrong by slicer.
 

Z offset between supports and object wrong by slicer.  

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Despx
(@despx)
Active Member

Good morning,
I print very small objects and often need supports.
I noticed that PrusaSlicer incorrectly calculates the Z offset between the supports and the object.
If with layer 0.06 mm I set the value of 0.2 mm of z offset I get a distance between the last layer of the support and the bridge layer of the object of almost 0.6 mm which for my prints is absurd. A correct value should be about 0.2 - 0.36 mm.
I understand that most people print very large objects and don't care about half a millimeter but there should be better accuracy from PrusaSlicer.
Another thing, why the synchronize-with-object-layer function can only be used with Z offset = 0 mm ??
It would be very convenient to have greater precision in the calculation of the Z offset. Is it not possible to unlock this function also for Z offset greater than 0 and leave the user the right to use it or not?

Below you can see the calculation error of the z Offset of the supports:
value set in the program 0.2 mm
value obtained by the slicer 0.59 mm!!

Best regards

Despx

 

Last support's layer

Bridge object's layer

Posted : 10/05/2021 6:30 pm
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(@)
Illustrious Member

I suspect you are not considering is the thickness of the various extrusions themselves. Supports often use variable layer heights and the preview doesn't capture what is really happening. It's better to measure the actual print for these types of specifics.

However - if you feel this is a defect, hop over to GitHub and post a bug report there. Include your files that demonstrate the issue so the devs can reproduce your findings. The devs don't look at this forum very often, and never for bug reports.

Posted : 11/05/2021 5:57 am
Despx
(@despx)
Active Member

@tim-2

Unfortunately there is full correspondence between what I see in the slicer and then in the print in fact the bridge layer of the object often collapses due to the excessive distance from the support and the next layer does not stick and delaminates.
In any case I see that in the forum I am not the only one to have various problems with the management of supports in PrusaSlicer, for example these other two topics have the same problem as mine:

https://forum.prusaprinters.org/forum/prusaslicer/prusa-slice-2-3-supports-problem/

https://forum.prusaprinters.org/forum/prusaslicer/bad-support-surface-bug-or-wanted-w-picture-josef-look/

It is really frustrating to see all the hours spent designing a 3D model in the best possible way ruined during printing due to a stupid bug!

I don't understand why programmers don't read this forum so I'll try again in GitHub but it seems to me that they enjoy doing like the three monkeys ... 🤨 

Regards

Despx

Posted : 11/05/2021 7:20 am
fuchsr
(@fuchsr)
Prominent Member
Posted by: @despx

I don't understand why programmers don't read this forum so I'll try again in GitHub but it seems to me that they enjoy doing like the three monkeys ... 🤨 

Hey, maybe they're just busy actually programming instead of reading scores of posts with questions about bad first layers or "bugs" in Prusaslicer that are 99% traced back to STLs with errors...  

To understand this specific issue better, would you mind sharing the 3MF project file? Supports are a weak area in PrusaSlicer and I'd like to better understand what you're seeing here. Save STL as 3MF and zip it before uploading it. Thx,

-r

Posted : 11/05/2021 12:14 pm
Despx
(@despx)
Active Member

@fuchsr

Hi, I have already sent all the necessary files on GitHub several hours ago and after some messages the matter has been clarified in a profitable way ... we just have to wait for the ver. 2.4.0 😉 

Best regards

Despx

Posted : 11/05/2021 2:17 pm
fuchsr
(@fuchsr)
Prominent Member

Great! I'll look it up on GitHub. 

Posted : 11/05/2021 2:20 pm
Despx
(@despx)
Active Member

My only regret is that I cannot thank rtyr for his patience because he closed the report. 👍 👍 👍 👍 

Posted : 11/05/2021 2:25 pm
Neophyl
(@neophyl)
Famed Member

You *can* still post to a closed issue and anyone who is subscribed to it will still get a notification, so you could still do that 🙂

Posted : 11/05/2021 3:21 pm
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(@)
Illustrious Member

@despx

github issue link, please ...

Posted : 11/05/2021 5:18 pm
Despx
(@despx)
Active Member

@tim-2

https://github.com/prusa3d/PrusaSlicer/issues/6465

Posted : 11/05/2021 5:50 pm
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(@)
Illustrious Member

@despx

Curious - that report suggests the distance never changes; I change my setting every time and it is honored by the slicer. I set 0.1 I get 0.1, I set 0.01 and I get 0.01. But the Prusa printer understands variable layer height. Does the Ender? 

Posted : 11/05/2021 10:03 pm
Despx
(@despx)
Active Member

The problem in my opinion is that PrusaSlicer manages the thickness of the object layers, support layers and bridge layer differently.
The layers of the object respect the setting given by the user instead the layers of the support are managed internally by the slicer and do not have the same value as those of the object but a height calculated so that between the last layer of the support and the bridge layer there is the space indicated in the Z offset of the support. The problem, especially in the printing of small objects, is in the bridge layer which is printed with the height equal to the nozle diameter, so the slicer adds the nozle diameter to the Z offset, as a consequence if the user sets as Z offset 0.2 mm, the slicer will calculate 0.2 + nozle diameter.
This calculation in some cases (mine and others who have found it) can cause the bridge layer and the next layer to collapse and the print is damaged by delamination at that point.
For this reason, in ver. 2.4.0 will make it possible to use synchronize-with-object-layer and optionally the bridge layer as the first layer after the support or a normal solid layer (as already happens in the case of soluble supports).
In practice PrusaSlicer will allow you to do what find in Cura, Simplify, etc.

Best regards

Despx

Ps: I hope my bad English was clear 😊 

This post was modified 1 month ago by Despx
Posted : 12/05/2021 9:07 am
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