Is there a good way to make a "perfect" dome? Since a UV sphere has poles, the best way to make a &quot;perfect&quot; sphere is subdividing a cube and casting it to a sphere, so there is no pinching. You can make a hemisphere by deleting the bottom half.
However, the vertices don't go around it in flat rings, so I can't use this method to make, say, a top third of a sphere.
Is there a better way to make a third of a sphere without a pole at the top?
You can instead just use the boolean modifier in order to cut away the quad sphere. It should still keep all-quad geometry but the faces near the cut could be squished.
Important notes:

Using subdivision surface on a cube will not give you a perfect sphere. The corners will always be slightly lopsided.
Instead: Enable the &quot;Extra Objects- Mesh&quot; addon inside Edit-&gt;Preferences-&gt;Addons. This comes with Blender. Then, when you add a new object you can choose &quot;Round Cube&quot; inside the mesh section. Choose that, and switch the operator preset to &quot;quadsphere&quot; to make a truly round quadsphere.