If I sweep a section along a rail that is rectangular, MOI leaves holes at the corners whereas Rhino creates mitred corners with no holes. Is this by design?

Make a filet on the rectangle before the sweep :)

Hi Steve, this is a limitation currently in MoI's sweeper.

It takes extra work to handle mitering the corners and I haven't had time to set that up for version 1 of MoI.

It is something that I intend to add though.

There are various work-arounds, for example use 2 rails with corners for a 2-rail sweep instead, but the easiest for now is to use Rhino for that kind of sweep.

- Michael

A simple rail revolve makes the trick :)

The rail revolve looks OK except that it scales the profile depending on how far the edge is from the centre of revolution.