Supports on a slanted surface - failing
 
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spiff72
(@spiff72)
Trusted Member
Supports on a slanted surface - failing

Hello all,

I run into this issue frequently when supports are needed above a slanted surface.  See attached image and 3mf file.  Is there a way to make the supports not be placed in a way that the bottoms of them are floating in midair?

Posted : 22/10/2020 4:03 am
spiff72
(@spiff72)
Trusted Member
Topic starter answered:
RE: Supports on a slanted surface - failing

3mf wouldn't attach - sorry.  Here is another image unsliced showing the feature that it is trying to support.

Posted : 22/10/2020 4:05 am
Neophyl
(@neophyl)
Famed Member
RE: Supports on a slanted surface - failing

You need to zip up most file types like 3mf files or stl files r the forum doesn’t accept them. 

Posted : 22/10/2020 5:10 am
spiff72
(@spiff72)
Trusted Member
Topic starter answered:
RE: Supports on a slanted surface - failing

HP_Stands_Shell_102120a

 

Here is a 3MF file (zipped)

Posted : 22/10/2020 12:01 pm
Neophyl
(@neophyl)
Famed Member
RE: Supports on a slanted surface - failing

The thing is those features at the front do not require support and will print fine (well they would on my MK3).  I think even the top under section with the steep bridging would print ok without support, just be a little rough, in an area you cant see anyway 🙂  Prusa Slicer is over aggressive on supports and they will grow outwards from the feature they are supporting, however as they are on a slope of the part it cant handle that as it is dumb and doesnt extend them down (the lower layers are already sliced by that point so it only goes down as far as when the support was started which is why it hangs in the air).  As I say though you shouldn't need supports at all for those anyway.

Also one thing about the support settings you were using (the defaults) that contact distance of 0.1 will absolutely weld them to the part, especially with petg.  You need minimum of 0.2 to have even a hope of separating them. 0.25 would be even better.  I've attached a modified 3mf file with a support enforcer for the top to only generate supports there and I changed the support angle to 90 degrees as it makes them more stable with this model (short zig zags rather than a couple of long ones from side to side of the part).  Personally Id turn support off as I think it will print without.  Any any supports with petg are usually a pain to remove.

Other changes I made was to increase perimeters from 2 to 3, and decreased infill.  Perimeters make a part much stronger than any equivalent infill increase.  This will result in a stringer stand that prints in less time.

Anyway take a look and print it if you want.

Attachment removed
Posted : 22/10/2020 1:08 pm
spiff72
(@spiff72)
Trusted Member
Topic starter answered:
RE: Supports on a slanted surface - failing

Thanks for those tips.  I think I understand WHY the slicer wants to put supports in there, since the notches in those sloped ribs will create a weird overhang (just where the notches are).  I will check out your 3mf momentarily.  

The part finished printing since I posted, and the part turned out fine despite the terrible supports.  I will be tweaking those default support settings because you are correct - the supports have been difficult to remove on my parts!

Posted : 22/10/2020 1:30 pm
spiff72
(@spiff72)
Trusted Member
Topic starter answered:
RE: Supports on a slanted surface - failing
Posted by: @neophyl

The thing is those features at the front do not require support and will print fine (well they would on my MK3).  I think even the top under section with the steep bridging would print ok without support, just be a little rough, in an area you cant see anyway 🙂  Prusa Slicer is over aggressive on supports and they will grow outwards from the feature they are supporting, however as they are on a slope of the part it cant handle that as it is dumb and doesnt extend them down (the lower layers are already sliced by that point so it only goes down as far as when the support was started which is why it hangs in the air).  As I say though you shouldn't need supports at all for those anyway.

Also one thing about the support settings you were using (the defaults) that contact distance of 0.1 will absolutely weld them to the part, especially with petg.  You need minimum of 0.2 to have even a hope of separating them. 0.25 would be even better.  I've attached a modified 3mf file with a support enforcer for the top to only generate supports there and I changed the support angle to 90 degrees as it makes them more stable with this model (short zig zags rather than a couple of long ones from side to side of the part).  Personally Id turn support off as I think it will print without.  Any any supports with petg are usually a pain to remove.

Other changes I made was to increase perimeters from 2 to 3, and decreased infill.  Perimeters make a part much stronger than any equivalent infill increase.  This will result in a stringer stand that prints in less time.

Anyway take a look and print it if you want.

Attachment removed

I already have this part printed, so "it's all good" at this point, but I am curious about the issue with Prusaslicer not being able to handle supports on the angled surface of a part...

Is this a bug in the software that will eventually be addressed?  Or it is just "the way it is"?  I tried dumping that same model into Cura 4.7.1, and it does a much better job of handling those supports:

 

Posted : 26/10/2020 8:33 pm
Neophyl
(@neophyl)
Famed Member
RE: Supports on a slanted surface - failing

If you think it’s a bug then open an issue over on GitHub. 

Posted : 26/10/2020 9:51 pm
-- liked
spiff72
(@spiff72)
Trusted Member
Topic starter answered:
RE: Supports on a slanted surface - failing
Posted by: @neophyl

If you think it’s a bug then open an issue over on GitHub. 

I created an issue on Github 

Don't know if it will go anywhere, but I tried 😉

I did a quick "demo" model to try to demonstrate the issue on a smaller, simpler part but it didn't misbehave as badly as the model I shared in this thread.  I included both models in the 3MF file that I attached to the issue (along with a screen shot showing both of the support issues).

Posted : 27/10/2020 7:28 pm
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