Hi Ralf, just another example here of how to do a "Loft with guide rails" (as I would understand it) inside of MoI.

Say we have these 3 sections:



Lofting them will give this result:




If you want to have more control over the "sides" of how the shape is formed, you can draw in some guide rails along the side direction like this:



Now you can select the circles there, and run Construct / Sweep, and pick the 2 guide rails as the sweep rails, and then they will become the guides that are used to generate the shape, it will produce this result:




So one thing to note is that there are 2 modes for Sweep: "One rail sweep", and "Two rail sweep", depending on if you have picked either one or rails at the stage in Sweep where it prompts you to pick the rails.

If you pick 2 rails for the sweep, doesn't that give you the "Loft with guide rails" that you are asking about?

- Michael