I want to cut the hole with the boolean modifier but it's not working. Anyone have any ideas why?
Also, how can I trim a part from the model.
Here is my blend file:
It's a common problem with Boolean operation in blender; it won't work if there's incomplete or bad geometry. The problem is, the boolean is a prime culprit for CREATING the bad geometry.
Ensure your meshes have no loose geometry, remove doubles and dissolve messy faces/unnecessary vertices. Really inspect both objects before using Booleans.
By turning on surface normal lines you can spot weird geometry a little easier, if the line isn't quite centred, something is probably wrong.
I've heard that combining the Boolean modify with a solidify modifier creates better geometry.
I've highlighted the areas of concern - there's probably more. Lots of unnecessary vertices. Two faces ontop of each other (pairs of blue lines) Face normal pointing out across the surface from the vertices.
And inside the oval, you've got some faces that don't have normals, so they're a bit bonkers.. See second picture.
Everything should be neat shapes, quads or triangles preferably.
I feel for you, it's not nice when it happens.
Apart from manually dissolving bad faces, snapping unwanted vertices to existing vertices and then 'removing doubles', this post explains some of the problems with non-manifold geometry.
Started by removing the non-manifold face (in the middle) and manually recreating the center so that there we no interior faces.
I also used the knife tool on the one end to clean up the messed up 'mirror'. this allowed me to recreate the end shape as I believe it was desired.
To create this whole, your cylinder needs to NOT be a 'real' cylinder (with thin walls and an empty center) but a full cylinder. When the boolean modifier is performed, you should then be able to remove the hole as desired.