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I was trying to scale this tilted cube along global z-axis:

enter image description here

I scaled it by twice with S+Z, the result ended up being:

enter image description here

I was baffled as clearly not only it scaled in z, but also in y.

Please help me comprehend this behavior. What does locking z-axis actually do? Why doesn't the result look more like:

enter image description here

?

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  • $\begingroup$ Scale in object mode can not alter the inner geometry above along object axis. You should do that in edit mode or apply the rotation before scaling. $\endgroup$
    – lemon
    Commented Feb 22, 2020 at 16:05
  • $\begingroup$ @RobinBetts, whatever the transform orientation is (here global Z), if the object is rotated (here 45 degrees) it won't become a diamond. Or am I missing something? $\endgroup$
    – lemon
    Commented Feb 22, 2020 at 17:46
  • $\begingroup$ @lemon Crikey! Why's that? (Just goes to show I never scale in Object Mode) An explanation of why scaling the object's transform matrix in Z behaves this way would earn a UV from me.. unless I'm missing something... why does the resulting scale include Y but not X? $\endgroup$
    – Robin Betts ♦
    Commented Feb 22, 2020 at 17:58
  • $\begingroup$ @RobinBetts, answer provided... please, if I'm wrong, give yours (will learn something, really). Additional question: have you ever scaled in object mode, Robin? ; ) $\endgroup$
    – lemon
    Commented Feb 22, 2020 at 18:30

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As far as I know object scale can only be done along its own axis (X, Y and Z).

So if we have this cube orientation (rotated 45 degrees around Y for instance):

enter image description here

it cannot be scaled in the global Z axis only.

That's why we have this result:

enter image description here

So to obtain the wanted diamong shape, you need to either:

  • Apply rotation CtrlA and choose 'rotation'. Then scale along global Z:

enter image description here

Or:

  • Enter edit mode, then scale along global Z:

enter image description here

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    $\begingroup$ but... but... in object mode, it's scaling in 2 of its axes.. just not the one it has been rotated around. :( ! I'll have to multiply out some matrices by hand in the console to try and get my head around it. This must be so basic.. and I've never noticed it! $\endgroup$
    – Robin Betts ♦
    Commented Feb 22, 2020 at 19:22
  • $\begingroup$ You definitely can have a transformation matrix that scales in a diagonal direction, @RobinBetts. Just not in Blender. $\endgroup$
    – John Dvorak
    Commented Feb 23, 2020 at 1:32

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