Hi Lish, since that is a planar cut, you can use Construct / Planar to build a surface there and then join the pieces together.

But in MoI, the Planar command needs to have a fully closed outline.

So beginning with this model:



Draw a line snapped between these 2 ends:



Now select the line, and the edge of the surface to form a closed loop, then run Construct / Planar to build this:




You can now delete that line segment. Then select the 2 surfaces and use Edit / Join to glue them together into one single object.


It is a lot harder to fill non-planar holes, MoI does not have the full equivalent of the SolidWorks Fill command yet to fill more freeform areas, it is something that I do want to add in the future though.

- Michael