Few days ago was a discussion to draw an octahedron, whwt is inpossibile in Shapr3D.
Here is a gemetric solution , with draw on face and use subtract tool.

Need the hatched triangle to subtract from the cuboid.

Thank you Attila for your contribution/proof. Quite honestly I didnâ€™t understand the negative claim of the other post. Almost like a Christmas troll? Nor did I understand why the approaches shown were not accepted.

Have watched your video once and will have to watch it again so it sinks in.

I had issues in the past doing polyfigures but found a solution when the capability to deform sides/surfaces was introduced. Will take a try at this one.

Discussion and contributions are great. Thanks againâ€¦

Is the b = 2R around the square a definitional feature of an octagon? If not, how do you know this? Is b the full diagonal or is it half of the diagonal? Thanks

a sphere drawn around it: r=a/2xsquare root2
The diagonal=b=2h=2r=a x squareroot2
In the octahedron the grinding angles are 90 degree.
That is why I edit the â€śhâ€ť with tehe outside square radius.
But most important it was made by geometric and got sharp result infront off the squareroot2 is infinite decimal burst.
Brg.
A