Let me start by saying I am new to all this..so no answer is too obvious -- nothing is obvious to me.

I have extruded an ellipse and then at the extruded end of the resulting body I have revolved an arc and its offset entity.  Think about the arm of a wind anemometer connecting to the cup on the anemometer.  Because of the curved inner surface of the cup the arm protrudes on the inside of the cup.  How do I remove that protrusion?  I would think I want to trim the arm end to the inside surface of the cup...but I can't make that happen.