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Negative Volumes  

Kurt Matson
New Member
Negative Volumes


I am using negative volumes and a pause to insert magnets into a print.

The problem I am having is that the position of the negative volume has to be pretty accurate and each time I move the negative volume cylinder in PrusaSlicer it disappears! The object obscures the view of the negative volume. 

Is there a way to position the negative volume more accurately? For example, can you make the model a bit transparent so you can see where you are putting the negative volume, rather than guessing?

Any help would be much appreciated. 🙂


Posted : 18/03/2023 11:40 pm
Active Member
RE: Negative Volumes

I center my part on the grid and then use the move command to line up the neg volume with the grid lines. It has worked so far. 


Posted : 19/03/2023 12:48 am
Famed Member

If the part is your own design it's always best to incorporate the space in the original file.

If you must place them in slicer use the Object manipulation coordinates in the right hand pane for accurate positioning.


Posted : 19/03/2023 6:47 am
Famed Member

Unfortunately not.  It was a feature request I put in to github quite awhile ago though as I find the same problem.

There have also been a few others requests for basically the same feature. etc

The only work around is to place meshes in your design software in the correct positions and then split to PARTS and then change the parts to negative volume type.

This post was modified 2 days ago by Neophyl
Posted : 19/03/2023 9:05 am
Estimable Member
RE: Negative Volumes



I agree with Diem and Neophyl,

However I don't consider placing meshes in your design software in the correct positions a workaround, I consider it the proper way.  It's best to do this in your CAD software, and change the imported part to the type you need, e.g. negative Volume, Modifier, Enforcer, etc,,. (with it already positioned correctly).

If however you Don't know how to use CAD "yet", you can use this workaround in PrusaSlicer, But learn CADD or you will suffer.



For this example we'll use the bunny model in the Shape Gallery.


First make sure PrusaSlicer is in expert mode,  then right click on your Platter, Add Shape/Gallery/and select the bunny.stl, select OK.

Next right click on the Object, select "Add part" and add a "Box", once added make sure the box is dropped to the Platter. ( It should be by default but its always good to check) then just move the box out of your way while keeping it on the Platter. I usually just  push it to the back left corner.

Next, Right click on the bunny Object, and select "Add negative volume" and add a "Cylinder" you can scale it if you like. It doesn't matter at this time.

Next in the "Sidebar" go to the Object menu. In there you should have.

<Object> bunny.stl

            <Part> bunny.stl  <--- This one

            <Part> Generic-Box

     <Neg Vol> Generic-Cylinder

Now Select the <Part> bunny.stl and right click on it, Select "Change type" and from the resulting menu you can choose "temporarily" to change the part to a:

Negative Volume: Gray

Modifier: Yellow

Support Blocker: Red

Support Enforcer: Blue

All of these types are See-through. If any of  them are selected they will turn from their Base color to Green See-through.

For this example I'm going to suggest Selecting "Negative Volume" from the menu as this will give the highest contrast when placing thee negative volume for your Magnet.

After positioning your Magnet (Neg Vol) Select the bunny.stl (Neg Vol), and "Change type" back to a Part, If your certain that your done positioning your magnet you can also delete the Box we added in the beginning of the tutorial. The box acted as a placeholder while we changed the type of the bunny.stl Slicer always wants to have a Part on the Platter.


Now your all set to slice.



Use the Move Gizmo to position the Neg Vol for your Magnet, while parts can only be selected from the Object menu, Negative volumes, Modifiers, & Support Enforcers/Blockers can be selected directly on the Platter. Using the Move Gizmo will give you the control you need in all directions.

As long as your Not using 2.6 alpha (you shouldn't be) then I will recommend that you can, and should also use the "Part manipulation" pane to more precisely position your parts.

If however you are trying to do this in the 2.6 alpha I can only wish you luck, as the coordinate system in the alpha is currently a complete mess and the results will be pot-luck.


Anyway Hope this helps, and learn CADD.




Posted : 19/03/2023 3:47 pm
Kurt Matson
New Member
Topic starter answered:
RE: Negative Volumes

Thank you, Henry, Diem, Neophyl and R&D !!!

I create all my own meshes but didn't think of placing one mesh inside another.

Changing the type to a negative volume after the import is the trick. This method is what I was looking for. Thanks 🙂

Having said that I think it would add lots of functionality to PrusaSlicer if the negative volume were visible while you moved it inside another mesh. 

Awesome forum.

Thanks Again. 😎❤️👏

Posted : 20/03/2023 2:04 am