Hi Steve - yes definitely those pieces are not touching each other smoothly, they are coming together at a crease.

When you do the polygon export, switch the display: option to Display:Shaded, and you can see the crease a little easier there when lines are not being displayed along the edges.

This is just like the sharp edges where faces of a box come together - just welding won't normally change this.

To get this to be a smoother object, I'd generally recommend trying to build the upper part that is supposed to be smooth all in one single surfacing command, like all one sweep. That tends to make it easier to get a smooth model there, it is difficult to make thing smooth when building in little pieces.

The other problem is some of the pieces are not quite exactly aligned with one another, the halves seem to be overlapping a bit (which is hard to see unless you zoom in a bit), instead of touching exactly. That makes it hard to join the pieces together also.

I'll see if I can come up with an example of a different approach.

- Michael