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I need to use half of a sphere, but I can't figure out how to cut it in half. The best I can do is remove one quarter of the sphere.

With a UV sphere, I scale it to my requirements, apply the scale $1.0$, enter Edit Mode, press Numpad 5, then Numpad 1 to switch to Front Orthographic View, position the cursor above the center top, drag to select half, press Del, and choose Vertices.

What am I doing wrong?

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5 Answers 5

Reset to default
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One way.. (I'm always using this for mirroring)

enter image description here

  1. Alt-LMB select edge loop
  2. V rip, with your cursor on the waste side of the loop.
  3. Hover, and L select connected under cursor
  4. X delete faces.

.. which can speed stuff up, sometimes: you can do it from any view.

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  • $\begingroup$ Thanks. Being fairly new to all this I had to work out that LMB need to be pressed when pressing ALT key. $\endgroup$ Commented Jun 14, 2021 at 22:42
  • $\begingroup$ Hello @John! I've linked out to the relevant area of the manual. You've prompted me to go back and browse it a bit myself. Even though I'm not as new to it as you are, the manual keeps throwing up useful surprises for me, in the fundamentals ( selecting, snapping, viewing, etc. ) $\endgroup$ Commented Jun 15, 2021 at 7:05
  • $\begingroup$ In this version there's only a few things to care for: if you instead want to delete the upper half, you might not want to move the selected edge loop. So, after hitting V to rip the loop, hit ESC (or RMB) so it stays in place from where you ripped it. If you then hover over the upper half and press L, the lower edge stays selected (which might not be visible since it's in the same location as the edge loop connected to the upper half). That's no problem if you delete faces afterwards, but if you delete edges or vertices than the top row of your bottom half will be gone, too. $\endgroup$ Commented Jun 15, 2021 at 9:11
  • $\begingroup$ @GordonBrinkmann Ahh! my muscle memory is so embedded I didn't notice these possibilities. Yes, It's delete faces, not verts or edges. But I was struggling to reproduce your selection of one half and opposite edge.. in the end I realised, without thinking, my cursor is always on the waste side of the loop before invoking Rip. And I always drag a little to ensure the rip has happened and I have the right side selected, even before right-clicking to drop the selection in place. Escape key is too much of a stretch for me :) $\endgroup$ Commented Jun 15, 2021 at 9:41
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    $\begingroup$ I guess for people new to Blender it's not so obvious that the cursor defines which edge will be selected after ripping. But since you can press L over whatever part you like it isn't important. Only in this case one has to be aware of different selection methods of Blender, because L adds to existing selections instead of replacing them. I think, in Blender when a selection is added and when it's replaced is sometimes not obvious for new users, too. Anyway, your answer is perfect, especially because no orthographic view is needed and you can even easily create slices of the sphere. $\endgroup$ Commented Jun 15, 2021 at 9:54
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Bisect.

Will throw the bisect operator into the ring.

enter image description here

For the top or bottom halve of the default cylinder could bisect using local origin (or any point with z = 0) and normal aligned with z axis.

The clear inner / outer remove geometry below / above the plane defined by point and normal. Both will leave only the cut.

Fill, fills the cut.

The threshold keeps original geometry if within.

Can define and cut on any bisecting plane.

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    $\begingroup$ So many ways to do this. $\endgroup$ Commented Jun 14, 2021 at 22:44
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You need to check the option to include hidden vertices in your selection: https://docs.blender.org/manual/en/2.91/modeling/meshes/selecting/introduction.html#selection-modes (Also called "X Ray"-Mode)

The Hotkey is Alt+Z.

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    $\begingroup$ This answer, or go into Wireframe mode. $\endgroup$ Commented Jun 14, 2021 at 10:39
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  1. Set the view to Front Orthographic (Numpad 1)
  2. Set the viewport shading mode to Wireframe (Z4)
  3. Press Tab to switch into Edit Mode
  4. Enable Vertex Selection
  5. Select one half of the sphere
  6. Remove the selected vertices by pressing X and choose Vertices from the menu
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  • $\begingroup$ Step 5 should probably specify the method of selection. Box selecting seems to make the most sense. $\endgroup$ Commented Jun 14, 2021 at 16:47
  • $\begingroup$ @R-800 I don't agree. While using box select is likely to be the most common or useful method, it is entirely possible that another selection method is more convenient/correct given the situation ; we cannot assume that the simplest example applies to OP's situation. Blender provides multiple selection methods and the user is expected to be capable of choosing the method most applicable to his situation. tl:dr method of selection constrains the answer without improving it. $\endgroup$ Commented Jun 14, 2021 at 22:10
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You can use Geometry Nodes to create a hemisphere by removing all vertices (or points) with a Z coordinate less than -0.001.

Or using a Curve Cirlce and Arc node:

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