difficulty to get a clean geometry

[pascalchap]

Thank you Micheus,

I didn't realize that the intrude command works like inset but for the complete object.

I read the post 'help - radial mirror inner faces' before posting my question. To avoid the trouble explained in the post, I "dissolved" the edge linking the external and internal faces at the top of the lamp before mirroring the half lamp (shown in step 6). So there was only one face selected before mirroring and I though it will be enough to build a correct model.

To your question why I chose to build only one face rather the complete object, I must say that it is because I am not sure of the complete process I will use:

This model should be included in a Povray scene ( Yes, I still use PovRay), and I was, at the origin, thinking to export only one face, and build the complete lamp inside povray, to limit the number of faces to load.
But, as I said, I want to add holes and bumps to the model, so I think I will have to smooth the model, and when I do this with the slice, I get bad results, so I tried to rebuild the complete object, and forget why I was working on a single slice.

Following this discussion, I think I will continue with the intruded cylinder, and extract a slice at the end, if it is useful.

Thank you for the answer.