Simplifying and closing open polysurface of detailed topography

Hello all!
I am a college student trying to CNC Mill a topography map out of baltic birch plywood. I imported a 3d print file, scaled and cut it to the proper size, and then converted the mesh to a polysurface. In order to CNC it, I would like to simplify the file greatly and need it to be a closed polysurface. I have tried intersecting the surfaces and then lofting the curves to no avail but I am also very limited in my ability.
Happy to send the file but it is .3gb so I cannot attach it. Here is the link to the file.

Thank you! Sorry in advance for my poor execution.


ID: 1b517cca-abdb-4d2a-84d6-6545b0166d6b (4)
Object name: tttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttttt
Layer name: polysurface model
Render Material:
source = from layer
index = -1

Invalid polysurface.
open polysurface with 112986 surfaces.
One or more surface normals are not oriented.
Edge Tally:
5 boundary edges
171028 manifold edges
= 171033 total edges
Edge Tolerances: 0.000 to 0.001
median = 0.000 average = 0.000
Vertex Tolerances: 0.000 to 0.001
median = 0.000 average = 0.000
Render mesh: 112986 meshes 342063 vertices 115686 polygons
Created with fast meshing parameters.
Analysis mesh: none present

Well, my main comment is that your approach is not optimal. I would not have converted the mesh into a polysurface, I would machine directly on the mesh. Many CAM programs can toolpath directly on meshes, RhinoCAM for example. The file size will also be much smaller. You also do not need closed objects to CNC machine, open surfaces or meshes work fine. I have machined many terrain meshes similar to what you show in your image.


I would also attempt to mill the mesh.

However if you really want a surface, you can do this in a few simple steps.

I deleted the sides and the bottom of your object so only the topography was left.

Then I exploded the mesh and duplicated the borders. With the borders still selected I created mesh faces with Mesh from Polyline. I joined everything, ran AlignVertices with a distance to adjust of 0.01 mm and finally stitched a few points and the resulting mesh should not have any internal open edges anymore.

I created a surface below your mesh and from here on Iā€™d use Grasshopper.

The surface is divided as many times you want. The points are projected vertically onto the mesh and a surface from points is created.

A simple way to join the three dimensional surface with the horizontal base is by creating a bounding box of both objects and boolean difference the terrain surface with flipped normals.

The result is a more or less smoothened, lightweight polysurface.

The Rhino file below contains the mesh I rebuilt, a planar base surface and the baked polysurface from Grasshopper.

surface_rebuild.3dm (4.9 MB) (14.0 KB)