Hi Kimmo, welcome to the forum!

The sweep is having problems because you're doing them in separate pieces, if you do it as all one single sweep it should work better for you.

To do it as a large piece you will need to form a long joined curve out of those edges - to do that select the edges and then run Edit > Join - that will create a new long curve object and those are the ones you want to use for your sweep rails. when you do just that one long sweep it should be better formed.


The sweep will make a kind of funky sharp lip on the result though, is that what you're trying to do?

It's more typical to use filleting to round off edges rather than trying to make them manually with sweeping. That would go something like this - starting with just one surface:



Select that surface and run Construct > Extrude to punch it out into a solid:




Select the top face of the solid and run Construct > Blend to round off that top edge:




Something along those lines is a more typical type of construction.

- Michael