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I have a simple rounded edge prism. I created a circle to use as the "knife" because I want to cut 2 holes through the prism.

I first select the circle, then select the prism, go into ortho view, click tools -> knife project, to cut it:

enter image description here

Nothing happens after cutting it except making an extra edge in the shape of a circle:

enter image description here

What am I doing wrong? Why is nothing getting but? What do I need to do to cut THROUGH the cube?

Thanks.

WindBJ
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    A knife cuts geometry - which you must understand as adds extra edges and points. It does not cut through objects. I think what you describe you want to do is Boolean https://docs.blender.org/manual/it/dev/modeling/modifiers/generate/booleans.html – Patdog Mar 25 '17 at 21:31

1 Answers1

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After using a Knife Project tool check the Cut Trough checkbox in the Tool Shelf (T). enter image description here

If you place the cutting object on the 'clean' face it'll make the hole. If the cutting object is placed so it's overlaping the edges of the cuted object it'll create a geometry (edges) on it (as @lemon mentioned in his comment).
enter image description here

Paul Gonet
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  • ...and that gets a wow from me :) – Patdog Mar 25 '17 at 22:40
  • In fact... I don't get how you obtain that. I knew this cut through option before but here this is not making a hole, just circular cuts (added edges) for both front and back faces. How do you obtain what can be seen in your gif? – lemon Mar 26 '17 at 08:07
  • @lemon Please see my updated answer, which explains how it works (for me at least :)). – Paul Gonet Mar 26 '17 at 17:56
  • @PaulGonet, thanks for this complement to your answer. But it does not work for me, even on a simple cube (a circle to cut in plain face of a cube). I always have created edges but no hole(s). Well, this is not really a problem as I can always delete the face but this difference in the behavior is weird... – lemon Mar 26 '17 at 18:04
  • One point regarding 'cut through' in knife project is that you should use an orthographic – b.reid Mar 18 '19 at 00:48
  • I'm finding it very frustrating that I am trying to do what you did with the cube - but with a cylinder. I just want to cut a shape out of a cylinder. When I use Knife Project, it selects the vertices and edges under or behind the cutting object, but it doesn't remove them. – Tango Jan 17 '22 at 08:26
  • I ran into the issue where a hole would not be made but vertices would look as they were -- it was because I was trying to cut through a hole already made – Sludge Jun 09 '22 at 19:45