The setup is pretty simple. I start with 1 cube, two cylinders:
- Create a thick rectangle (Shift+A > Mesh > Cube > size to fit)
- Create a cylinder (Shift+A > Mesh> Cylinder > size to fit)
- Copy first cylinder mesh (Right click first cylinder > Duplicate object > move laterally)
In top view (Numpad 7), delete half of the second cylinder, leaving an array of faces. I then select all faces of the half-cylinder and extrude them (Tab for Edit mode > Delete half of the vertices on top and bottom, leaving a semi-circular face,
A to select,
E to extrude)
After exiting Edit mode, I drag both objects down through the surface of the cube. Using the "Boolean" modifier twice, I first find the difference between: (1) Right cylinder and cube, and (2) left..half..cylinder thing and cube, pressing Ctrl+A after each operation to execute the modifier:
The modifier clearly works with the unmodified (right) cylinder, while it does not work with the modified (left) cylinder. However, something is happening, because the top surface of the cube shows the outline of the modified (left) cylinder. Furthermore, if I zoom "into" the cube to look around the inside, there are no other faces there. I've tried right-clicking the modified cylinder and converting to a Mesh, but this still doesn't work.
What am I not seeing? How can I fix this?