1 Perimeter, 0 Top & Bottom, Open to the Inside
 

1 Perimeter, 0 Top & Bottom, Open to the Inside  

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TheRooster
(@therooster)
Active Member

Is there a way to use modifiers to get Prusa Slicer to print this STL file...

 

...to look like this?

I want to essentially chop off the tips of the pyramid shaped divots in each side.

I've tried setting the main print settings to 1 perimeter, 0 top and bottom layers, with 0% infill and then putting a modifier cube in the middle with 0 perimeters, top and bottom layers to 0, but the slicer ends up putting a perimeter around that modifier cube, like this...

I essentially want a modifier cube that just kills all extrusion inside it, and doesn't make the slicer build a perimeter just outside of that cube.

It seems like I've had this happen in the past, but maybe not intentionally. Now I want it intentionally.

Posted : 26/10/2020 6:03 am
Neophyl
(@neophyl)
Noble Member

Modifiers work by in effect changing the slicing into different areas so thats how they work. 

Can I just ask why the hell are you not using some software that is actually designed for modelling to you know, model ?  Rather than using a slicer which is designed for slicing.  Its like trying to cut some wood with a craft knife.  Yeah you can do it it but the effort is going to be more and the result isn't going to be as good.

If I had to modify that shape I'd remove the top and bottom faces in blender to leave a non manifold shape, add a cube in the middle and use it as a boolean cut to trim the pyramids off and then add a solidify modifier to make the resulting skin thickness as required.  Done.  Oh and then export naturally to get the stl.  Very simple and low effort.  Hell attach the stl, lmk how thick you want the walls and roughly how much of the pyramids you want left inside and I'll edit it.

Posted : 26/10/2020 7:23 am
towlerg
(@towlerg)
Honorable Member

So easy in PS, create a box modifier, size and position to the center, set fill to 0%, set bottom, perimeter and top layers to 0. Post the .stl and I'll create a .3mf ready to slice.

Posted : 26/10/2020 11:46 am
Neophyl
(@neophyl)
Noble Member

@towlerg

Thats exactly what he described doing but I agree that he should post the saved project file he is using or at the minimum the stl file.

Posted : 26/10/2020 12:40 pm
towlerg
(@towlerg)
Honorable Member

@neophyl

Sorry but I was just confirming that what he wanted to do was possible. If the OP knew how to do it, he wouldn't have posed the question.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Posted : 26/10/2020 1:01 pm
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 -2
(@-2)
Illustrious Member

@towlerg

Except tower - he has tried exactly that and is saying the modifier has a problem.  I've run into this issue a dozen times. It is a pain.  But, as neo said, it would be a lot easier to simply design the part right in the CAD tool in the first place. 

At issue is which faces end up as internal or external. The slicer can't decide what is inside versus outside, so places perimeters on semi-random faces.  It is the cube void within a cube problem: to our eyes, it is easy to say the inner face is external, but when the slicer gets there, it is an internal face and the volume should be filled, not a void.

Tower, if you have an example of making this work, please post the 3mf.

Here's is a quick attempt showing one of the possible outcomes ...

CubedVoid

But I think what the op is trying to get is those windows with an internal divot - basically vase mode with a top layer.

 

 

This post was modified 1 month ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 26/10/2020 3:20 pm
TheRooster
(@therooster)
Active Member

@neophyl

First, I'd love to upload files. I don't see how to do that though. I'm probably just missing it though.

Second, like tim-m30 said, I basically want vase mode, but not vase mode because there will be "islands" during printing which don't work with vase mode. Have you ever tried "hollowing" out a solid model and then slicing it? When your goal is single wall thickness, hollowing only works on vertical walls. If your goal is a 1mm thick wall, angled walls end up being more than 1mm thick when sliced horizontally.

Third, this is just a sample file which easily explains my purpose and goal. The actual file I want to work on is a lot bigger and more complex.

 

Posted : 26/10/2020 4:05 pm
TheRooster
(@therooster)
Active Member

Am I unable to attach stl or 3mf files because I'm too new?

Posted : 26/10/2020 4:13 pm
Neophyl
(@neophyl)
Noble Member
Posted by: @brian-b24

Am I unable to attach stl or 3mf files because I'm too new?

I dont think so.  You do however need to zip up stl or 3mf files or the forum doesnt accept them.  About the only file types it likes are pictures and even then it can be finicky sometimes.

Posted : 26/10/2020 4:17 pm
TheRooster
(@therooster)
Active Member

Test_Cube

Here is the 3mf file with the 25mm cube with divots and the 20mm cube in the center with what I thought should be the correct modifier. But when you slice it, you see the perimeters around the internal cube.

Posted : 26/10/2020 5:02 pm
--
 -2
(@-2)
Illustrious Member

Yep - the cube is a solid. So when you clip a chunk out with a modifier, the new face is towards the inside, at the boundary of the void you are placing. Totally expected behavior.  Where do you expect the new face to be?

It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 26/10/2020 5:21 pm
TheRooster
(@therooster)
Active Member

I didn't expect anything. I was hoping that the modifier wouldn't cut out a chunk of the solid cube before shelling it, but instead just modify the extrusion behavior within the cube. What I want is a way to make a shell of an object with the ability to "cut" holes in the side of the shell.
To get a shell, the object must be solid.

This post was modified 1 month ago by TheRooster
Posted : 26/10/2020 5:40 pm
--
 -2
(@-2)
Illustrious Member

I made this, but was in a hurry and made the shell 1mm, should have mage it .45 mm ... but, it shows how it works.

Cubed

This post was modified 1 month ago by --
It is always wise to get more than one opinion... as for trusting Prusa? No way man....
Posted : 26/10/2020 5:40 pm
TheRooster
(@therooster)
Active Member
Posted by: @tim-m30

I made this, but was in a hurry and made the shell 1mm, should have mage it .45 mm ... but, it shows how it works.

Cubed

Now try and make that so that the part is made by 100% single thick extrusion walls. Make your external perimeter 1mm wide and see if it slices... Spoiler alert, it won't make a single wide wall. You can tweak your extrusion width to 0.5mm for a 1mm wide walls and it will make a double pass (full loop) but the sloped walls will have gap filler between them because sloped walls are greater than 1mm thick in the flat plane.
Believe me, I've tried this both by solidifying the exterior planes and by hollowing out the original solid object. It doesn't give me what I want.
So, back to my original question. Is there a way to make a modifier that just cuts out the extrusion and doesn't cut out a chunk of the solid model?
My goal is to take a relatively large model, with lots of details, and quickly print a shell of that model. To do that and not end up with a flimsy print, I increase my external perimeter width to 0.9mm and print with 0 top and bottom layers and 1 perimeter. (You should try it, it's a really useful way to print if your models are compatible.)
Using your method (which again, I have already tried) I end up with some areas with holes because it ends up being thinner than two extrusion widths, and other areas with gap filling between the two extrusions. So not only does the print take over twice as long (0.45 extrusion width x2 to make 0.9mm walls) but on the sloped walls, it takes even longer because it has to go back and fill the gaps.

Posted : 26/10/2020 5:53 pm
TheRooster
(@therooster)
Active Member

I still have two replies that are awaiting moderation, so I'll try and summarize here.

I want a single wall shell. Like vase mode, but not actually using vase mode because I don't want one continuous extrusion from bottom to top. The only way to do that is to have a solid model, like when making a vase using vase mode. But I also want to cut holes in the side of that shell.

This file is a simple example of what I want to do. So hopefully there is a way to do what I want. If not, then I'd like to request a way to do it from Prusa.

Posted : 26/10/2020 5:57 pm
TheRooster
(@therooster)
Active Member

...and now that I have enough posts to not be a newbie, there is an "Attach file:" option. So yeah, new forum accounts have to use the "Add Media" button to attach zip files.

Posted : 26/10/2020 5:59 pm
Neophyl
(@neophyl)
Noble Member

@brian-b24

Attached are 2 versions one with .45 walls and the other with 0.9 walls.  The .9 wall version slices with a single perimeter if 'Detect thin walls' is enabled, otherwise it doesnt like the corners as when an angle changes its actually smaller than the average wall thickness (which is why domed structures also have iisues with even wall thickness).  Making it thicker is very easy in blender , as I can just type in a desired wall thickness so if you want it tweaking its a 2 second job.

Posted : 26/10/2020 6:18 pm
Neophyl
(@neophyl)
Noble Member

Exceeded the edit time.  No you cant use a modifier to do what you want and its not really the slicers job.  You should learn to use some modelling software, that way you can do what you want much easier.  Slicer for slicing and CAD for modelling.  

Posted : 26/10/2020 6:21 pm
Neophyl
(@neophyl)
Noble Member

Played around with the thickness options a bit and got an even better one from a sliced with single perimeter point of view.

 

 
This post was modified 1 month ago by Neophyl
Posted : 26/10/2020 6:28 pm
-- liked
TheRooster
(@therooster)
Active Member
Posted by: @neophyl

Exceeded the edit time.  No you cant use a modifier to do what you want and its not really the slicers job.  You should learn to use some modelling software, that way you can do what you want much easier.  Slicer for slicing and CAD for modelling.  

Dude.

That's twice you've told me to "learn some modelling software." That's quite the assumption you've made and not helpful. I know how to use pretty much all of the modeling software. I do use Blender, which actually has a pretty crappy solidify modifier when models get complex. Even with the "even thickness" checkbox checked.

So unless you have actual advice other than "get good", you're no help at all.

And in opposition to your thought that this isn't what slicing software is for, I think that this is exactly what slicing software is for. I am trying to modify how the slicer recreates a solid model. I want to turn off the extruder in a specific area. Trying to modify a complex stl model to mimic a single extrusion shell by solidifying it is a fool's errand. That is the definition of a hack. It might work for some models, like my simple example, but isn't a robust solution.

Maybe, just maybe, I know what the hell I'm talking about and asked a specific question in order to get a specific answer. Either Prusa Slicer can do what I'm asking, or it can't. If it can't, that's fine, but I'd like to request a feature to do what I'm asking for. I don't think it's unreasonable.

I'd like a way to "cut" a hole into a single extrusion (vase-like) wall using a modifier object.

Posted : 26/10/2020 6:50 pm
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