Separate in two parts a Mesh using Knife Project

Question

How can I separate this mesh:

Using this plane:

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

Objective:

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.

EDIT

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?

Related - http://blender.stackexchange.com/questions/5320/cutting-a-mesh-in-half, if it's not strictly needed to use the plane. — Mr Zak, Nov 23 '16 at 19:50

score 4 · Accepted Answer · edited Jun 10 '20 at 12:57

4

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):

edited Jun 10 '20 at 12:57

Community

1

answered Nov 23 '16 at 18:42

JakeD

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Sorry for misunderstunding, I modified the question, I'm trying to separate the mesh in two parts, not only cutting throught it. – Fabrizio Nov 23 '16 at 18:50
Ok, I'll add that to my answer in just a second...I am preparing some gifs for you. – JakeD Nov 23 '16 at 18:54
Isn't there a way to select the above mesh with an operator or something that can be done with a code? – Fabrizio Nov 23 '16 at 19:13
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: http://blender.stackexchange.com/questions/50591/how-to-select-part-of-a-mesh-by-using-a-helper-plane – JakeD Nov 23 '16 at 19:24
DIdnìt understand the examples in the given link – Fabrizio Nov 23 '16 at 19:32
Do you understand the techniques using "circle select" in my answer? – JakeD Nov 23 '16 at 19:35
Let us continue this discussion in chat. – JakeD Nov 23 '16 at 19:44
If using Bisect it's simpler to choose Clear Inner or Clear Outer options in the operator settings to delete the rest or to use the trick from the linked question. – Mr Zak Nov 23 '16 at 21:25
@MrZak Good idea, and if done programmatically, duplicate, then bisect both...one with clear inner and one with clear outer. – JakeD Nov 23 '16 at 21:29
Sorry this post is a little old but this is the most appropriate for my issue. My goal is exactly the same, split a mesh in two part but not only with a simple line (so I can't use Bisect tool) but also with a curve (that's why I need to use Knife Project tool) and with scripting, so I can't imagine to unselect parts that I don't want etc. My post : https://blender.stackexchange.com/questions/208095/split-a-mesh-with-a-curve-knife-project-tool I tried your solution JakeD with a Knife Project tool – Millhow Jan 14 '21 at 08:37