Inverse Negative Volume
I'm very, very new to all of this, so fair warning!
I feel like this should be a simple thing to do, but perhaps I'm thinking of it all wrong.
I messed up a print earlier and would like to finish a small section of it and attempt to glue the pieces together. The section I'd like to reprint is a small area that can easily be described by taking a cylindrical cross-section and effectively "cutting" the rest, keeping what's inside the cylinder.
In PrusaSlicer, I can easily create holes by adding Negative Volume Shapes, but ideally, I'd like to "invert the mask" so to speak and keep the "hole" while cutting the rest of the object.
A good example of this would be if I had a cylinder and instead of making a "donut", I'd like to make a "donut hole", discarding the "donut".
RE: Inverse Negative Volume
Possible but not totally trivial. You can use your model itself as a negative space and cut out from a larger object. So in your example of a donut hole, you have to use a part that is slightly larger than the donut hole, then load a donut as a negative volume and overlay it, which will leave the donut hole.
RE: Inverse Negative Volume
Aha, thank you! I was actually on the path to doing just that, but I couldn't figure out how to save my modified model out to an STL, so I could select it as a negative volume in the menu. Whenever I save out my model to be re-used later, it doesn't save the sliced version, "merged" - instead it saves out the two separate objects I used to create the slice.
I know, I have much to learn, lol!
RE: Inverse Negative Volume
I had a similar need, where i wanted to apply a negative volume, and then add a part to the model. I finally chatted with Prusa, and they told me I could not do that.
Apparently the negative space is always dominant, and I too tried to save the file as a "merged" STL ... but it would not allow that. 🙁
RE: Inverse Negative Volume
Just do it in cad. It’s a simple task On e you are familiar with whatever software you go for. Something like this would take a few minutes to set up in blender.
RE: Inverse Negative Volume
I downloaded an stl vase that turned out to be filled on the inside.
No problem, I loaded a second copy and shrank it in x & y but left z alone. I left z alone as I wanted the waist to shrink horizontally but not vertically.
The only side effect was I lost the floor of the vase. Is there any way to load a second copy of an stl, slice the bottom off and then treat it as a negative volume so I can keep the floor? Or is there another way to use negative volumes so that the floor is retained? Shrinking in z doesn't do it as the sloping walls intersect in undesirable ways.
RE:
Two thoughts:
1. Make a copy of the model, shrink it in x and y, use cut to remove 1 mm or what at the bottom. Save, then reload as a negative space and align it with the original model.
2. The model is probably meant to be printed in vase mode. So you don't have to remove the innards, just turn vase mode on.