# Scale along Z-axis only

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

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

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:

?

• 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. Feb 22, 2020 at 16:05
• @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? Feb 22, 2020 at 17:46
• @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? Feb 22, 2020 at 17:58
• @RobinBetts, answer provided... please, if I'm wrong, give yours (will learn something, really). Additional question: have you ever scaled in object mode, Robin? ; ) Feb 22, 2020 at 18:30

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):

it cannot be scaled in the global Z axis only.

That's why we have this result:

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

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

Or:

• Enter edit mode, then scale along global Z:

• 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! Feb 22, 2020 at 19:22
• You definitely can have a transformation matrix that scales in a diagonal direction, @RobinBetts. Just not in Blender. Feb 23, 2020 at 1:32