Help needed with clipping planes and mesh objects


#1

Hi, I used a structured light scanner to scan one side of a virtually identical six sided finial, i.e all six sides are the same. My thinking was to minimize scan time by using one scan.

My plan was to employ two clipping planes, set at 60° to each other, to remove all poorly scanned surfaces, and then use polar rotate to create the six sided object.

Questions:

  1. Can I actually use polar rotate with meshes or does the mesh have to be converted to surfaces first, and if so, with what command?
  2. Why do the clipped away areas insist on reappearing when I erase the clipping planes.
  3. Aren’t the clipping planes supposed to permanently erase unwanted areas?
  4. What is the difference between clipping planes and cutting planes?

#2
  1. ArrayPolar will work fine with meshes.
  2. & 3. Clipping planes are just a visual trick, they don’t modify geometry. You might try ExtractMeshFaces or ExtractMeshPart to get rid of the bits you don’t want.

I’m not sure I understand # 4

Sam


#3

@antons987,

in addition to Sams answer above, i guess you will need to split the mesh using real planes (which would be cutting planes). To create a plane surface from your clipping plane, use the command _Plane with _3Point option, then click on the corner points of the clipping plane.
You might have to enable End snap to get the corner points picked.

Once you have your cutting plane, which is just a planar surface, make sure it is large enough to split your mesh. The splitting can be done using _MeshSplit command.

c.


#4

Thank you very much, Sam & Clement, for clearing this up. I’m not sure “about #4” either…they’re two separate commands. I was BTW able to simply split the scanned object (essentially a six sided organic (toy) top by using Clement’s suggestion recommending the _MeshSplit command. It works nicely, but I’ll need to fiddle with my XYZ=0 alignment of the object to enable my first and sixth mesh edges to come together properly. I’m wondering (having not tried yet) whether I should be rotating 300° rather than 360°, which probably accounts for the object not properly holding after command execution. If I, for example, rotate through 180°, the resulting object sticks.
The endgame here is employing a rotary 4th (indexing) axis to CNC this object on a router, using Vectric Aspire. I’d import the completed object, scissor split one edge, laying the unrolled, flattened mesh down for toolpathing, then re-rotating the object and paths for machining. I have a ways to go.
I generally work primarily in AlphaCAM, but only Rhino offers the CAD power necessary here. Thanks again!


#5

I haven’t zoomed in yet for a close look, but does the MeshSplit command using a cutting plane leave re-sewn mesh polygon edges that aren’t ragged? That would be highly desirable for creating a 360° object.


#6

you must know that mesh splitting commands in Rhino are not very reliable and many times, especially with complex meshes, will not that well as or right now.

One thing you may try if your mesh is not super heavy is to use MeshToNURB to convert your mesh to Polysurface, use Rhino regular Split or Boolean commands, and then convert the result back to Mesh.
Sometimes MeshSplit or SplitMeshWithCurve would work fine…

-jarek