I build a primitive pool table model with holes where the pockets would be but cutting the holes via the Boolean modifier left me with really bad looking lines in the table surface.

enter image description here

I could very well take the time to smooth them out but I'd like to prevent them in the first place. How would I go about this?

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    $\begingroup$ What type of Boolean operation did you use? $\endgroup$ – Gwen May 23 '13 at 6:33
  • $\begingroup$ This might help. $\endgroup$ – Quazi Irfan Jun 10 '13 at 5:15
  • $\begingroup$ that looks like it shows the backfacing part of the slice too? If you subdivide the plane you use to intersect with, does that produce better geometry? $\endgroup$ – zeffii Jul 4 '13 at 12:04
  • $\begingroup$ Note, you are asking 2 questions here: 1) How to clean. 2) How to avoid the problem in the first place, both have very different answers and I think it isn't leading to such useful results, especially because the image shows an example which you are probably better off not using booleans for. $\endgroup$ – ideasman42 Jul 4 '13 at 23:39

The short answer:
To get nice results with booleans on polygons you have to make the two entities have a similar level of division. If you can align the geometry for both entities then you will get mostly clean topology too.

The realistic answer:
If you can get away with avoiding the boolean operations then you will learn a lot more about modelling, and you will work faster (have more control, and be capable of fixing issues). The idea of a boolean operation is more based in maths than in practical polygon modelling, but it is possible and can look good. Here is a quick youtube search for this topic

Booleans have become really quite nice in Blender 2.5+ onwards after implementing the CARVE library. But don't expect the convenience of a solid modeller like SolidWorks or other CAD packages that represent geometry internally as mathematical equations.

The time spent trying to line up two entities for a clean boolean might be better spent modelling by hand (in this case). Using a few circle polygons and a mirror modifier you'd be surprised how much easier this is to model - plus the added bonus that you can quickly change the geometry without having to individually boolean the whole thing.

example image
mirrored over x and y angle view

the geometry here isn't optimal if you want to bevel the sharp edges, that requires a bit of planning - and beyond the scope of this answer,

example .blend (shows all the steps to get the basic idea) At least when you do it by hand you can take into account that you might want to bevel a few edges and create the extra guiding geometry to do that.

Try doing a bevel on booleaned geometry, it's a world of pain.

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In your case, it looks like the large ngon is tessellated (which in this case blender internally converts into skinny triangles before running the boolean function).

So for better results you could make the large ngon into smaller. more evenly spaces faces, or if its not an ngon, just avoid having many skinny triangles as input since these tend to give worse output.

Also check geometry for sanity (normals pointing correctly, no holes in geometry)

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