Best way to cut a hole through an object?

Question

I need to create a cylinder, cut in half, with a hole cut out of it. I'm very new to Blender, and I'm sure that there are many ways to achieve the same thing, but I used a boolean modifier to remove the hole from the cylinder. The problem is that in the shape that I have, after selecting smooth shading, there are some unwanted diagonal lines above and below the hole that you may be able to see in the image.

My question is, is there a more efficient way to do this without a Boolean modifier? I have heard that Boolean modifiers are not a great tool as they can result in 'bad topology' so I would appreciate it if someone could suggest a better way to do this. I would also like to know if it is possible to have the smooth shading without these strange lines around the hole.

Thanks!

Answer 1

Two things to make this work

1. Keep the geometry all quads
2. Keep the quads pointing the same way (all up)

Cutting the shape using Knife project. Boolean would work too.

Repair topology - make it all quads. Using loopcuts and adding new vertices.

Final result - added edges are marked blue.

Answer 2

You are correct. There are many different methods and booleans can be tricky.

Check this very helpful tutorial: https://www.youtube.com/watch?v=Ci1jBOm_5NY&t=1s

Onto a curved surface, try going into front orthographic view and lining up a circle in front of your object. Then apply Shrinkwrap modifier so that the circle geometry wraps to the surface of your cylinder. You can then delete the new topology to create the hole.

With Booleans, often new, troublesome topology is created. You want Quads, not Tris or N-gons (more than 4 sides). When working with Booleans, you'll need to carefully check your new topology. Functions to be familiar with: Alt-M by distance (merge vertices), Select by Trait- Faces by Sides (>=4). The former function helps to clean up overlayed vertices. The latter function selects n-gons.