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I know this has been asked before - I've looked through and tested them all, and none works. I'm using Blender to create a medical implant for 3D printing. I need to make the inner and outer casing fit exactly, and have been using Boolean Difference to "subtract" the inner volume of the casing from the outer casing. Normally, Boolean subtract works, but in this case, it either gives the error message "Cannot execute boolean operator", or simply deletes the whole upper casing (see overview figure - can't attach more figures currently).

I've tried:

  • removing duplicate vertices (edit mode A, W > remove doubles)
  • recalculating the normals (edit mode CtrlN)
  • applying scale/rotation (object mode CtrlA)

Yet nothing works.
I know this has been already asked a lot, but I have yet to found a go-to guide to systemically troubleshoot to find the problems with Boolean operators. Any thoughts? Blender file attached.

object with boolean modifier

blender file

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  • $\begingroup$ If one of the answers helped you, you should mark them as answered or at least upvote them. $\endgroup$ – Samoth Apr 24 '16 at 21:19
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I add an answer to post pictures, here.

I checked your mesh, both shapes have some problems that could make boolean troubles... eg:

enter image description here

enter image description here

maybe try to fix those weird shapes...

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  • $\begingroup$ I smoothened the corner - no results there. For the edges in the middle of the ring - I've noticed them before, but they can't be dissolved - either nothing happens, or Blender gives the message "Invalid boundary region to join faces. I've messed around with this for long now - and nothing seems to work there either. $\endgroup$ – user2585222 Jan 13 '16 at 14:06
  • $\begingroup$ @user2585222 I am really new to stackexchage, so I do not understand why you add new answer instead of editing the first one, is it the recomanded practice? $\endgroup$ – atevm Jan 14 '16 at 16:07
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    $\begingroup$ @atevm, user "user2585222" didn't add another answer! I (m.ardito) added this answer. I wrote "I add an answer to post pictures" because mine is not really an answer, but it is the only way for me to add pictures to show what I thought was wrong in the model he (the OP) posted. $\endgroup$ – m.ardito Jan 14 '16 at 17:30
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In edit mode for both meshes participating.

  • Select Nothing.

  • Menu Select Interior Faces. You will see a few found faces.

  • Repair those faces. Remove Them.
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  • $\begingroup$ Thanks for the tip. Tried it, but no luck - still the whole upper case dissapears after Boolean difference. $\endgroup$ – user2585222 Jan 14 '16 at 18:44
  • $\begingroup$ Wtf, whatever you do, nothing works. $\endgroup$ – user2585222 Jan 14 '16 at 19:30
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Make sure, your mesh is non-manifold as right now it is not (meaning, it is manifold, meaning not water-tight)... The Carve library that Blender now uses internally for Boolean Operations has problems with manifold geometry.

Just select nothing in Edit mode and then hit Shift Ctrl Alt M (Select - Non Manifold, won't work with Face selection) and see what is getting selected. There are all your problems ;-)

Now you need to "water-tight" your model at these places by rearranging the connected Edges and Faces from the selected Vertices... This is manual work that can't be automated for you. See the answers to "What is non-manifold geometry?" for further help.

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