why can't I get smooth bottom?

 From:  Michael Gibson
2032.3 In reply to 2032.1 
Hi Olga, I think you may not have picked the top circle as one of the sweep profile curves.

That circle at the top helps make the shape to be a better rounded shape as the sweep comes to the tip.

Then I believe you should pick the 2 rounded outside pieces as the rails, and one of the side pieces as the scaling rail. (just as PaQ has shown above)

- Michael