Hi Pozero - Trim is one method you can use to cut things up. If it isn't working for you, please post a model file here and I can take a look and see what problem you're running into.

But actually the Boolean operations are probably what you want.

Here for example I have drawn 2 objects - a sphere, and then a line which will be used to cut the sphere:




To perform the cut, select the sphere first, then run Construct / Boolean / Diff. Now select the line as the cutting object and then click "Done" (or right click in a viewport which is a shortcut for pressing Done).

That will cut the sphere by the line and leave the pieces behind - select and delete the pieces you don't want. Here I have moved the pieces to show the result:



Hope this helps! If you're having problems with a particular model, please post the model file.

- Michael