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I can't get it to work using any of the existing answers to this question. I have a box that has been subdivided.

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I want to cut a square hole into it. I've tried using Knife Project and the Boolean modifier to cut the hole but I get the same kind of result. In both cases there are weird artifacts in the hole.

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In the other questions about this type of problem they were saying something about how the subdivision modifier works better with quads but I'm not sure what that means. They were trying to cut circles and I'm trying to cut a square and a square has four points so I was hoping it would just magically be a quad or something.

Can you advise on how to cut this hole?

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    $\begingroup$ I doubt that you need that many subdivisions for such a simple object. Use smooth shading and no more than 3 subdivisions on subsurf. Quads are polygons with 4 vertices, and yes try to use quads. Then the question for you is what shape are you expecting out of the "hole" a straight cut or a circluar one? $\endgroup$ – cegaton Jul 4 at 18:04
  • $\begingroup$ Here it seems that the boolean modifier is set before the subdivision. Try to invert that: place the subdivision modifier before. If using knife project (or other cut), you'll need to apply the subdivision firt. $\endgroup$ – lemon Jul 4 at 18:04
  • $\begingroup$ If you are learning blender try to avoid boolean operations as much as you can and learn proper modeling. Watch this video: 8 ways of cutting holes. $\endgroup$ – cegaton Jul 4 at 18:07
  • $\begingroup$ Following the comment by @cegaton, yes you should use bevel instead of subdivision modifier. That will round the edges without adding to many geometry in the faces. $\endgroup$ – lemon Jul 4 at 18:07
  • $\begingroup$ @lemon, tried it but I'm still getting the same thing. $\endgroup$ – user875234 Jul 4 at 18:09
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When 'they' say subdivision surface works best with quads, they mean that if you can get your pre-subdiv model to only use quad faces, you get a better result. Generally you would want to make the hole before applying the subdivision modifier. enter image description here

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To avoid 'cutting circles', you need to add supporting geometry around edges that you want to 'harden'. There are many ways to go about this. You can do it manually by simply adding additional edge loops and sliding them into place.

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You could also use a bevel modifier above your subdivision modifier in the stack.

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