# Create a plane perpendicular to the long diagonal of a cube

How can I create a plane perpendicular to the long diagonal of a cube? I have this which isn't correct.

Animation of plane perpendicular to the long diagonal of a cube (it should look like this).

Animation with audio of why. https://youtu.be/fWsmq9E4YC0?t=118

You can create a face-type Custom Orientation from any 3 points:

1. Edit Mode: Select the 3 points you want the plane to be aligned to and create a Custom Orientation from them.. ensure it's being used.
2. Object Mode: Select the plane, and Object > Transform > 'Align to Orientation'.

• This is the correct answer, but you have to use differents points for the orientation. Nov 10 '21 at 16:45
• Robin? Does that give the good solution? Nov 10 '21 at 18:09
• @lemon ... ahhh... Hope that's better, if that's what you mean.... Nov 10 '21 at 18:36
• Robin, yes. Many wrong upvoted answers here... but now that's ok Nov 10 '21 at 19:00
• Glad to see the best answer poping first :) Nov 12 '21 at 10:54

To rotate the plane so that it is exactly perpendicular to the long diagonal of the cube, one can use either a constraint or a little bit of trigonometry.

## Constraint

With the plane centered on one of the corners,

Add a Track To constraint and set the target to the cube.

## Trigonometry

Alternatively, one can use a short python expression to find the correct rotation.

First, rotate the plane around either the X or Y axis using the expression atan(2 / sqrt(2)) * 360 / tau.

Then, rotate the plane 45° around the Z axis.

• OMG ....are u math professor or why is this "a little bit of trigonometry"? +1 for "a little bit" ;) Nov 10 '21 at 6:07
• Two good solutions and the only ones to be exact here! Nov 10 '21 at 18:08
• only ones until Robin updates his answer... ;) Nov 10 '21 at 19:28
• @Chris Nope, not a professor. I hate math class XD Nov 10 '21 at 21:46

use math, cube is rotated to xyz axis correctly, create plane that is rotated correctly as well by default. Now, rotate it by 45 degrees on Y axis (or X), rotate it again on Z axis by 45 degree...

You end up with this and it is in right position. Set your orientation to Normal:

Now when you move with G+Z it will go this way

Now you just need to animate it on this movement and make it boolean cutter

• +1 sounds for me like the easiest solution... Nov 10 '21 at 6:08
• 45 and 45 does not work Nov 10 '21 at 18:09
• did you rotate it in right order? Nov 11 '21 at 5:03
• @MikoCG, yes. Have a look at HISEROD answer where the good angles are provided. Nov 11 '21 at 9:28

Rotate the plane 45deg on both X & Y axis, then snap to the vertex of the cube.

• 45 and 45 does not work... Nov 10 '21 at 18:09