I'm new to Inventor so it might be something obvious, but I've already spent a couple of hours trying to figure it out, and searching doesn't seem to yield anything helpful.
I'm creating a pair of spur gears using Gear Generator. I can see the preview of the gears geometry when I'm in the generator dialog. However, when I click OK and a new part is generated, I can't see any generated geometry in my assembly. The part seems to be empty.
It turned out that two cylindrical faces used to construct the gears were not quite in the same plane, so that generated gears wouldn't be touching each other. I added assembly constraint and it now works fine.