Hello,

Your model is a bit out of square, that may be causing a problem, but I recreated the area of interest. Remake the line drawing you used to Revolve but extend it downward on Z to give you something to work with that you can cut away at the correct time. Revolve your shape into a solid and make a copy of the solid. Hide a copy of the solid, and then run an Inset command on the inside surface where you want the line to position. Select the top and side line from the Inset command and select Join. This should give you a curve tracking the inside of your revolved shape. Then delete the inset solid and unhide the original solid and perform a Boolean Difference at the appropriate Z depth. You should be left with something like the picture. Keep in mind that more control points will not help your situation, if you need a video I think I can get one out shortly. Hope this helps.