why can't I get smooth bottom?

 From:  malvin
Thank you PaQ and Michael for your replies

I have tried the way PaQ adviced and it did work!!! Many thanks

PaQ, I meant the part where the smalest circle is located.
There it was not perfectly smooth. Now it is.

I wonder if I pick RS and the opposing curve for rails and 1 or 2 for scaling rail it turns out differently in this area next to the smallest circle.

Could you please tell me why?