It's my first question on Stackexchange :)

I've been using Blender for a long time now, but I'm still a big noob about it. I use it to create or modify future 3D prints for my personal use.

I'm facing a problem : I would like to separate a part from a model. I did this a lot of times : I select all the vertices and I click on "separate". But as you well know, when you disconnect a part from a model, you only get the outside of this part, because the faces sticking directly to the model simply didn't even exist.

Is there a way to disconnect a part from a model, but without those holes ? You know, a "closed" disconnected part, with the shape of where it was attached...

I did a simple example in those pictures, part separated from a cube


See ? I know it makes sense in Blender because all models are "empty", but is there any way to keep those parts "full" ? Thanks !

  • 1
    $\begingroup$ I don't know any way to keep the parts "full", but an easy way to patch that, is to select all the edges around the part you don't want to be empty, and then press the "F" key on your keyboard (F stands for fill) $\endgroup$
    Oct 26, 2020 at 23:08
  • $\begingroup$ Thank you Ethan, it could work on model with very few polygons, but when the model is very curvy, it doesn't work anymore $\endgroup$ Oct 26, 2020 at 23:39
  • $\begingroup$ that is true, I'm not sure what to do in that case $\endgroup$
    Oct 26, 2020 at 23:41
  • $\begingroup$ Thanks anyway :), but the problem with my issue is that the "data" I'm looking for simply doesn't exist, it has to be created... $\endgroup$ Oct 27, 2020 at 1:11
  • $\begingroup$ The Bisect tool is close to what you want but it cuts a straight line and it delete half of your object, but If you duplicate it and repeat the operation on the copy? $\endgroup$
    – moonboots
    Oct 27, 2020 at 7:48

1 Answer 1


Simply use an object with almost-zero thickness for a Boolean difference.
That will get you a clear cut, with 'filled' holes.

Using a 0,01mm thick plane for a Boolean difference enter image description here

  • $\begingroup$ Wow! That's really useful, and makes no sense at all! (Shows how little I use Booleans) .. and Intersect does the other side? Flipping normals doesn't seem to make any difference to the direction? $\endgroup$
    – Robin Betts
    Oct 27, 2020 at 9:23
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    $\begingroup$ Sure, that way no geometry is removed. But unless you worry about losing 0,001mm of geometry, there's no need. If the plane has at least some thickness, it reliably fills both parts (since it's a standard boolean) :). $\endgroup$ Oct 27, 2020 at 9:43
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    $\begingroup$ I suppose there's always Bisect with fill, but it's infuriating, trying to make both halves. $\endgroup$
    – Robin Betts
    Oct 27, 2020 at 10:03
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    $\begingroup$ I'm wondering if it is what he/she wants, as " I select all the vertices and I click on "separate"."... so the separation is based on existing vertices (?). $\endgroup$
    – lemon
    Oct 27, 2020 at 10:48
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    $\begingroup$ Like a non axis aligned version of this.blender.stackexchange.com/a/133136/15543 Could use a plane mesh as a proxy for the cutting plane. $\endgroup$
    – batFINGER
    Oct 27, 2020 at 11:07

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