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I'm new to Blender, so I feel I must be missing something. I'm modelling something that's bound for a 3D printer and I need to cut some specifically shaped (and spaced) holes in it.

I've tried knife, knife project, bisect, and boolean modifiers, all with limited success. Knife (and knife project) were particularly infuriating, as they worked great on the outside of the object, but when I needed to cut the holes on the interior they failed miserably. It seemed my only options were to cut nothing or all the way through from the current view. I finally got the surface I want, but only after hacking the faces to death with the knife and merging edge loops a couple of times. It left the mesh rather a mess...

Is there any better way to do this? What about cleaning up the mesh a little?

Desired result finally:
smooth, clean looking cuts alternate view

Ugly, underlying topology: ugly topology

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    $\begingroup$ The topology actually seems pretty okay to me (considering what you are trying to do). Most of the tris could probably be converted to quads with a quick Alt J (with everything selected in edit mode). What happened when you tried boolean modifiers? $\endgroup$ – gandalf3 Jun 19 '14 at 6:12
  • $\begingroup$ @gandalf3 I'm not sure I was doing it correctly, honestly. I fiddled with the options, trying to subtract an extruded version of the desired hole shape from the larger object. I think I may have gotten the right combo and just didn't know it. None of them looked quite right. I'll try it again next time around. $\endgroup$ – Alan Hensley Jun 19 '14 at 6:17
  • $\begingroup$ Maybe this question will help. $\endgroup$ – gandalf3 Jun 19 '14 at 6:22
  • $\begingroup$ Check out this addon, it makes working with Booleans so much easier. $\endgroup$ – GiantCowFilms Jun 19 '14 at 15:26
  • $\begingroup$ @user2926289 Holy crap... that looks great! Thanks for the link! $\endgroup$ – Alan Hensley Jun 19 '14 at 16:07
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No Knife!

In STL (the main 3d printing exchange format) everything gets triangulated, converting to quads is a waste of time.

BoolTool has been mentioned, it does add needed functionality to the Boolean Modifer (which can be unintuitive). If you have complicated geometry, curved surfaces with thickness into which you want to cut shapes, then that's a good way to go. But, if like in your image, you have a flat surface then modeling the negative space and snapping it into position and then reconnecting the faces might take the same amount of time.

Take your basic shape:

enter image description here

Then you model the negative space, in place. Learning how to use the snapping tools (vertex snaps in particular) will make modelling easier and speed it up.

I like to remove the object wall, place the negative space where it needs to be, then attach the wall again.

enter image description here

enter image description here

Then select an edge of the remaining opening by holding Alt and Right clicking, this selects the edgeloop if possible (usually it will). Then press F to fill this shape.

enter image description here

With the faces Filled you can press Ctrl+T to triangulate selected faces.

enter image description here

or tidier like yours

enter image description here

At first this may seem like a backwards approach, but when you have simple geometry to cut into the booleans are not the only approach.

Alt + F

docs: Meshes/Editing/Faces

Alt + F is like fill but acknowledges internal boundaries. Islands to exclude from the fill. enter image description here .

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I would try using the Bool Tool addon. it makes the interface more elegant, and generally speeds up the workflow, as well as making better cuts.

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