Hey I am fairly new to Rhino but I am trying to get a mesh that I have to be cut into a certain shape using a curve or surface and nothing I have tried seems to work. I found a couple of discussions suggesting extractNonManifoldMeshEdges, cullDegenerateMeshFaces, extractDuplicateMeshFaces and then using splitmeshwithcurve but none of these options seem to work. As well I tried the basic splitmesh and cleaned and repaired the mesh with a variety of commands. Any thoughts or suggestions? Here is the mesh (sorry for the wetransfer link its too big for a direct upload):
Hello - you don’t say what shape, and I do not see any curves in the file…?
In any case the meshes are bad - (Check command) they have many duplicate faces for example and non-manifold mesh edges… this will take a bit of work, I would say.
-Pascal
In this case I need to cut it with a couple of different curves, but they are generally just rectangles of varying size. I know the mesh is not good but it was sent by a client and can’t be redone on my part. I am trying to get them trimmed to size to 3d print. Any suggestions on how to go about simplifying them to be trimmed?
fiber single.3dm (1.0 MB)
As well, here is just a single fiber so the wetransfer doesn’t have to be downloaded, the principle is the same and even a single fiber can’t be split as is it seems.
Right - the meshes are no good - in Rhino it is probably simpler to sort out one fiber and array the good one. Even better would be to get a curve or polyline from the top face of the zig-zag and array that and trim it with your rectangles using CurveBoolean. then extrude the results, and mesh that.
I’ll see if I can make you an example.
-Pascal
Ah ok that makes sense, not too sure how to do that but if you wouldn’t mind making the example that would be super useful 
Hello - It may not be so bad - in the Top view, select the wires and run MeshOutline - sit back and wait for a bit and then when it’s done run SimplifyCrv on the result.
You can then trim the curves with whatever shape and you’ll need to close them off so CurveBoolean might be a good way to go, with a closed curve or curves as the cutters.
Then ExtrudeCurve > Solid=Yes .8 units, all at once. Then Mesh the result.
Fibers (both directions)_Maybe.3dm (1.4 MB)
-Pascal
Ok this was super useful thank you so much! rhino is awesome but there are so many features it is a bit overwhelming sometimes