PrusaSlicer doesn't like slicing this obj file
Hey all,
I am generating an .obj file from Three.js. PrusaSlicer can load it just fine. However when I go to slice, I get these weird gaps in the print. I get an even worse result with STL even after running the STL repair.
I am 99% sure this is an issue with my file rather than PrusaSlicer, I am just struggling because the only time the letters go all funny is after slicing, they render fine in Blender for example.
Has anyone seen this kind of issue with slicing before and can give me some clues about what is going wrong?
Many thanks indeed.
Leo
Before slicing:
Sliced:
In Blender:
RE: PrusaSlicer doesn't like slicing this obj file
Run blenders 3D print tool analysis on the file and see what it comes back with.
RE:
Thanks for your reply. Here is the result of that tool:
Non manifold edge: 3034
Bad Contig. Edges: 0
Intersect Face: 1077
Zero Faces: 92
Zero Edges: 4
Non-Flat Faces: 5
Thin Faces: 57
Sharp Edge: 0
Overhang Face: 3395
I wasn't aware of this tool, that is very helpful! Using the "Make Manifold" cleaned up the model and it slices fine... However now I need to work out what is going wrong in Three.JS to cause such a poor output (I can take that to the ThreeJS forum though of course).
RE: PrusaSlicer doesn't like slicing this obj file
Non Manifold edges are the killer for slicing. While a slicer 'may' be able to guess what needs fixing with those its a gamble. One that usually you lose.
Even Netfabb often 'fixes' them incorrectly depending on the geometry. I'm not familiar with three.js but its usually related to boolean operations performed. You have to be extremely careful with those in Blender too (or any other software).
Any yes that 3d print tool is VERY handy 🙂
RE:
Boolean operations in which faces are coincident are a common cause for those errors. Here's a good explanation from the OpenSCAD manual.
Note: It is mandatory for all unions, explicit or implicit, that external faces to be merged not be coincident. Failure to follow this rule results in a design with undefined behavior, and can result in a render which is not manifold (with zero volume portions, or portions inside out), which typically leads to a warning and sometimes removal of a portion of the design from the rendered output. (This can also result in flickering effects during the preview.) This requirement is not a bug, but an intrinsic property of floating point comparisons and the fundamental inability to exactly represent irrational numbers such as those resulting from most rotations.
The solution (at least in OpenSCAD) is to add a tiny amount to the dimension of one of the Boolean partners, so they overlap.
Of course, there are other possible causes for errors in the STL.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE: PrusaSlicer doesn't like slicing this obj file
Hm, ok! Thanks for the useful pointers, much appreciated.