I have a very complicated mesh from a 3D scan, so I didn’t make it. I’m kind of new to Rhino and I’ve mostly worked with NURBS or SubD but I want to 3D print this model but in two halves (I’m attaching some photos), I tried MeshSplit and BooleanMeshSplit but they both resulted in bad meshes, I used the Check command and it said that the mesh had extremely short edges and Mesh has 1 face where the face normal differs substantially from the vertex normals. or disjoint edges. I tried UnifyMeshNormals and RebuildMesh but it didn’t work. Could someone help with a way to split this model in half so the resulting meshes are good to export as an STL for 3D printing. Thanks!
Here you can share the file then the guys will be able to help you.
Hi, I tried to upload it but it said the file was too big
I usually try these commands:
SplitDisjointMesh
and delete small pieces
CollapseMeshFacesByEdgeLength
Edge Length = document absolute tolerance or longer
AlignVertices
is also sometimes helpful.
“face normal differs…” mostly doesn’t matter, sometimes is disappears with unweld
completely (180°) and RebuildMesh
Sometimes it works, if the splitting plane (a line is sufficient) is moved by document absolute tolerance several times.
A search in this forum e.g. for Mesh + Repair could give you some more useful hints.
Understanding Meshes is not easy
zip it, otherwise wetransfer or whatnot.
hi, the zip file was still too big, this is the wetransfer link Unique Download Link | WeTransfer thanks for the suggestion!
you did not include the plane you want to use to split it. so i can not test it. if you can very slightly modify your mesh and lose a very very little amount of precision you can try to use Shrinkwrap
set to 0.7 edge length which is probably one of the fasted ways to rebuild your mesh here then try again. you also try the command ReduceMesh
with something like 70% and see if the detail wtill work for you or use more or less. or use Quadremesh
with 450000 faces, all worked here but took quite some time to complete. i did not attempt to split it since i would try to split with that exact plane rather. you can still post it here (the plane only) that should be small enough to upload directly here.
edit: i tried a cut plane as close to your image as i could and tried with the shrink wrapped version, i have a mac studio m1 ultra and after 2-3 minutes that came back splitting it successfully in half with 2 closed valid meshes.
thanks for all of your suggestions, I’m not quite sure I understand what you mean in the first paragraph. Why do I need to rebuild the mesh? The issue was coming up after I tried splitting it in half, when I used Check on the 2 halves it came up with the issues I mentioned in the original post. But before that the model was fine, I’ve already 3D printed it as a whole and it came out well and exported to STL fine. So not sure why I would need to ShrinkWrap or the other things you mentioned before splitting, I’m probably missing something. The exact position of the plane isn’t too important as long as it’s close to splitting it in half (like in the photo I posted) How did you split it into 2 good meshes? Thanks for your help.
?
if you want it to work without doing anything you are not at the right place, we are not dealing with black magic here.
I think its just a lack of understanding of all the factors involved. Many of us know that splitting a mesh (adding, removing, or moving vertices) may create problems that were not present in the original mesh. For someone without a full understanding of what is happening, the act of splitting causing problems may not make sense.
if an action leads to problems then all the factors have to be reconsidered, since there are only 2 parts to this story (mesh and splitting) one of them may be the issue. i am not really sure we should expect people not to manage to think that far i hope.
Thanks so much for your help! Using SplitDisjointMesh to delete the small pieces worked!
Thanks to everyone who helped! After using SplitDisjointMesh
on the two halves, I was able to export the STL without errors.
Just to clarify my original question—since the un-split model exported and printed fine, I thought the only issue was with the split, which is why I was confused about needing to adjust the mesh beforehand. I was just trying to split it without causing new issues, and since the model worked fine before, I assumed that I had thought far enough to deduce that the issue was with the split. Like I have previously mentioned I am very new to working with meshes and know I need to do more research., I understand that splitting can cause issues not previously present, I was just troubleshooting and seeking advice from those with more experience, rather than resorting to black magic. I appreciate the constructive help!
since your check reported that something happened with the mesh you have only one option to change here (the mesh) there is nothing you can do to make split work better here itself. (or probably almost not, sometimes it might help changing the tolerance settings but that is near black magic, at least to me.)
rhino has many methods to fix something, shrinkwrap being one of them besides all the other mentioned and maybe more. shrinkwrap rebuilds the mesh and can help if you run into such issue which you should apply before splitting since shrinkwrap tends to work better on closed meshes. the method you used might be maybe better, but good to know as many options as possible, you might run into more issues at some point.
may i ask what that scan is?