Imprint Solid?

 From:  Michael Gibson
3024.4 In reply to 3024.1 
Hi OSTexo, here is a quick demo of a different way. Note that this produces a depth that goes straight in one direction.

But one easy way to get a "custom capped extrude" is to extrude a face that you have trimmed out of a piece rather than a curve.

You draw the curve first, which is planar, off to the side like this:

Select the surface and run Trim, pick the curve as the cutting objects and then Right-click or push done at the "Select pieces to discard" prompt to keep all the pieces.

So that leaves you with a separate cutout piece, like this:

Now you can select that face and run Extrude. Note that in your case you will have to do this twice because you are crossing between 2 faces and not just one, and you can only extrude a single face right now and not a set of them.

Once you extrude the face, it will be a solid, like this:

Now you'll want to select the front face of that solid and delete it, and it will now be a pocket that is ready to be joined to the main piece:

Trim can be unreliable when you are using it with a curve that is not planar and is also not quite exactly aligned with the piece that is being trimmed, so it does not work well to trim your particular case with the bent curves you posted, that's why I was asking if you had the original planar curve still around. It's better to trim with that one.

- Michael