Hi niko, here's an example of how to use that technique with a curved rail, this is how to build the second example I posted entirely in MoI.

I started by drawing a polyline snapping its points on to the rail like this:



Now sweep along the polyline, it will build a mitered result like this:



Select just the edges around the original juncture point, do a Ctrl+C and then Ctrl+V to duplicate the edges as regular curve objects, and then delete the segmented sweep, giving you this:




Now use the Transform > Orient command to copy the starting rectangle to the very end, or actually you could do it by duplicating those edges from the sweep as well:




Now it is ready to sweep, use Edit > Separate to break the rail into individual pieces, and do the sweep in sections, first one sweep here:



Then a second one here:




That's how I produced the attached 3DM file created only in MoI.

- Michael