Hi Tom - If the ends of your loft are not closing then that means your curves are not flat planar shapes, are they bending around somewhat? Automatic capping only generally happens with planar shapes. If you can post the .3dm model file I can see if that is your problem.

One thing that is a lot different with the approach in MoI than in a polygon modeler is that you use booleans a lot more in MoI.

It can be easier to keep caps and such in place by doing booleans to carve pieces away from an initial solid.

So for instance in your case, I would probably go like this:

Start with a profile drawn in the front view. I drew half of it and the used mirror to make the other half. After you do the mirror you can also turn on points for the original half and edit them and see the mirror update, that is kind of a good way to adjust proportions and such. When you are done adjusting, select both mirrored pieces and use Edit/Join to glue them together.



Now use Construct / Extrude to punch out your shape into a solid. I enabled the "both sides" option so that it extrudes from the center out to either direction:



To make it tapered, I will carve away pieces using a boolean operation. To do this, switch to the right-side view, and draw a line at an angle that divides the shape, then mirror it to the other side, like this:



Now you can use those lines to cut the shape and remove material - to do this, select the base ring object, then run Construct / Boolean / Diff, and select the 2 lines as the cutting objects. This will slice the ring into 3 pieces, delete the outer 2 pieces and you will have this:



To get your beveled interior, I would temporarily hide the main shape, then switch back to the Front view, and use Construct / Offset to build an offset curve from the original:



Now just repeat the above steps to construct a similar extruded + tapered cut version of this inside offset curve. But reposition the cutting line slightly to the side so that this new version will be slightly larger than the original, that will give you these 2 different solids:



Select them both and use Boolean Union to make them into one solid.

I hope this gives you some ideas - like I mentioned one of the biggest changes is using boolean operations a lot for regular operations, this is a big shift in mindset from poly modeling where you usually want to avoid booleans as much as possible.

Sometimes you can do fancy surfacing by drawing outlines and then surfacing the outlines, but to start with I would recommend building things more like I have shown here, with different pieces each as individual solids, and then use booleans to cut solids into pieces, or to fuse different solid components together into the final shape.

- Michael