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(note : my understanding of manifold is that the object is solid, closed. Tell me if I'm wrong)

I'm working in an industry. I use Blender to adapt ingeniery/simplify CAD 3D models of a power plant for making virtual tour. Part of this work is about making a cut in the plant (like a cake you cut a part to see the inside).

The 3D models are very complex and requires a lot of work to be manifold (because the CAD software we use makes ugly 3D, with disconected faces and the vertices rarely are where they should be). I don't have the time to make all of them manifold (a power plant is a lot of machines...).

If no error of me, Blender Boolean requires Manifold geometry, and I can't always have it. So to boolean-cut I'm stuck in using 3DSmax where there is the « Boolean » tool, which accept non-manifold geometry (edit: but just cut, it doesn't create new faces).

It's a pain to switch between 2 3D softwares, and I would like to continue using Blender. Is there a way in blender to cut non-manifold geometry?

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I will demonstrate my approach on Suzanne so that it is a bit more complex than say, a cube.

  1. Setup the "knife cutter". For this I use a simple mesh with 3 vertices. Notice that the cursor is set to the pivot point for easy rotation control.

enter image description here

  1. Perform the knife project.

enter image description here

  1. Clean up the cut out vertices. Notes: use wireframe mode so the selection goes "through" the mesh, don't select the verts along the cut line...just the ones inside.

enter image description here

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  • $\begingroup$ I'm happy with, thanks :) Here a variation of your 3rd step; after cut you can select the vertices of the cut and then Ctrl+E (Edge Split) to divide in two parts (most of the time it work) $\endgroup$
    – LeDucSAS
    Commented Dec 13, 2016 at 8:52
  • $\begingroup$ Correction of what I said : your 3rd step works better than using edge split $\endgroup$
    – LeDucSAS
    Commented Dec 13, 2016 at 10:42

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