I have this weird object (vascular tree) which is empty inside, but closed from the top and the bottom: Object empty inside However, it is empty inside, which makes me unable to use boolean on a bigger object (I want to make a hole in an object through which this object will go through). So I thought I should fill it and then try to boolean. But, how do I fill it?

Thank you sincerely.

  • $\begingroup$ I believe that you are treating the Boolean operations of Blender like other CAD packages, that don't allow these operations to be done on a water-tight mesh, rather than a geometric "Solid". Booleans within Blender do have their limitations, and do not always work (when the mesh gets complex especially). However there are methods to do what you are intending to do as an end goal. Unless I'm missing the point of what you are asking here... $\endgroup$ – Rick Riggs Apr 6 '16 at 23:03
  • $\begingroup$ @RickRiggs would you suggest using a CAD package then? Do you have any specific software in mind? I would appreciate your idea. $\endgroup$ – i'm using tilt controls Apr 6 '16 at 23:05
  • $\begingroup$ I would go ahead and go thru the steps Duarte's answer provides. If you still have trouble, then post back, as there are usually always a way to help you within Blender with this big/knowledgeable community of users(In this case there are manual methods if your cleanup exercise fails). $\endgroup$ – Rick Riggs Apr 6 '16 at 23:45

All mesh - or 3D modeled virtual objects for that matter - are "hollow" or "empty inside" by definition, there is no such thing as mass, volume or matter inside them, with the possible exception of volumetric data like voxels or point clouds.

Boolean operations on meshes are always performed as a mathematical operation to simulate the existence of a dense "filled" object, by combining the surfaces of the intervening objects by cutting, intersecting and or subtracting them. These operations happen only on the "shell" or faces of the mesh surface, to give the impression of having dense matter inside them, when in reality there is none.

For that reason mostly only "closed" or watertight manifold meshes are easily usable in successful Boolean operations, outside of CAD applications that use either ACIS Solid Modeling, NURBS based surfaces or other geometry models more suited for these types of operations (and even these are all hollow as well, despite what the application may make you believe).

Open or inconsistent meshes (non-manifold) often give problems, errors, bad results, or fail completely.

That being said, in your case if you can't preform a Boolean operation on your object it is most likely either because your mesh is too complex, or there are some errors in your object like discontinuities, wholes, inconsistent normals, or any other problems that make your mesh non-manifold or non watertight and confuses the algorithm while calculating previously described operations.

What you need to do is clean it up and make sure these errors and discontinuities are gone. Stuff you can try:

  1. Removing doubles - Edit Mode > W > Remove Doubles, to merge all open or overlapping geometry

  2. Recalculate normals - In Edit Mode Ctrl + N to make sure all surfaces are facing the same direction consistently

  3. Check for holes - In Edit Mode press Space Bar and search for Select non Manifold. That should highlight any remaining wholes, or problems with your mesh which you must then solve by hand, like overlapping faces, inconsistent normals, missing geometry, etc.

  4. Ensure there are no coinciding or coplanar surfaces between the two operands - These usually confuse the algorithm making it unable to distinguish in from out.

After that your Boolean operation stand a better chance to produce good results, if your mesh is not too overly complex to successfully be processed. If that is the case the you should break it apart into smaller objects making sure that each and every one of them involved in Boolean operations is a watertight "closed" manifold mesh.


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