How can I separate this mesh:

Using this plane:


In two separate parts, the on above the plane and the one under?


What I want to achieve is to separate the mesh in two part like a boolean modifier (extruding the plane a little bit, in the way to have a 3d mesh instead of a 2d one) would do.


The hard part is to make two separate meshes using the separate by loose parts operator, like after a boolean difference operator as explained above.

Why I don't use boolean:

I cannot use the boolean modifier due to some non-manifolds (or overlapping) vertices and edges in the mesh.

Is this all possible or not?


1 Answer 1


After further research, I have decided to scrap everything that I had before (it isn't that complicated). You can see my edits if you'd like to see the "old" way.

1. Select all vertices

This is pretty self-explanatory. Make sure you're in edit mode, then hit A

2. Use the Bisect tool

Just drag and you should get a live display of where it will cut. (You can alternatively use the plane and knife project at this stage if you'd prefer. Just make sure to enable "cut through.") When you are done with Bisect or Knife Project, you should have the "cut" selected.

3. Rip/Tear the selected ("cut") vertices

For this step, hit V, then left-click before moving the mouse. This essentially makes a nice set of double vertices on the edge of the cut.

4. Select the top or bottom

Deselect all, then you can use the L select linked tool on the top or bottom. Make sure you get everything in the top including the half of the cut line.

5. Separate the mesh

Use P + Selection to quickly separate.

Here is the complete GIF (I finished the operation in 30 seconds):

enter image description here

  • $\begingroup$ Sorry for misunderstunding, I modified the question, I'm trying to separate the mesh in two parts, not only cutting throught it. $\endgroup$
    – Fabrizio
    Commented Nov 23, 2016 at 18:50
  • $\begingroup$ Ok, I'll add that to my answer in just a second...I am preparing some gifs for you. $\endgroup$
    – JakeD
    Commented Nov 23, 2016 at 18:54
  • $\begingroup$ Isn't there a way to select the above mesh with an operator or something that can be done with a code? $\endgroup$
    – Fabrizio
    Commented Nov 23, 2016 at 19:13
  • $\begingroup$ If you had the add-on that let you rotate the view, you could do it in one operation with the box select tool. For some other elaborate ideas see this: blender.stackexchange.com/questions/50591/… $\endgroup$
    – JakeD
    Commented Nov 23, 2016 at 19:24
  • $\begingroup$ DIdnìt understand the examples in the given link $\endgroup$
    – Fabrizio
    Commented Nov 23, 2016 at 19:32

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