Difference to union for 3D printing purpose

Hello everyone,

I’m new to blender. I would like to know if there is a quick way to have a boolean difference to union.
Let’s say I have a basic setup with a solidify cylinder and a cube.
My aim is to keep only one part of the cube going out from the cylinder.

Then I apply a boolean difference on the cube, selecting the cylinder as the cutting shape.

I then apply the modifier and delete the part I don’t want by selecting with L in edit mode.

Then I apply a union modifier to “merge” the cube and the cylinder. It works, but as geometry don’t overlap the result is not what I’m expected, I have that :

To test it, I’m using the 3d printing add-on and click on “Make Manifold”, and everything goes wrong.

Any help would be appreciated,

Thanks in advance,


Can you try and be a little clearer, especially with the screenshot. Why do you need to do both difference and Union?


Sorry if I’m not clear, my aim is to keep only the red part of the cube and the cylinder as a manifold mesh.