Let me start by adding, we have had a lot of newbies here who have come on board, asked a question and then disappeared, never to be heard from again. In your case, your original question was worded in such a way that maybe some of us took it the wrong way. For that, I apologize. When someone asks an open-ended question like "how do I do ????" with little or no information, it becomes quite difficult to answer. My early response was, "None" or something like that. Now that we have more information, it will allow us to give you the answer you were seeking. From what I gather, you are trying to "smooth out" more than actually sand your inside cuts. The one thing that I have found over the years is once you learn what blades to use, your cuts will be much smoother. Also as you become more proficient at scrolling, and that can only come with practice, your cuts will become much much smoother and will not require any sanding at all. Most of us sand both sides of our workpiece prior to doing any scrolling. That will eliminate trying to sand around areas that are very weak. Using a good reverse tooth blade in the correct tooth count will eliminate most all of the "fuzzies" on the under side. Buy yourself a small butane torch and very gently burn off the fuzzies that remain. Just be careful. I guess the best short answer I can offer is, take your time and learn the craft. You'll be amazed at how good you will get with just practice. I have looked back at some of the questions that I asked 7 years ago and I'm actually embarrassed that I asked them. But, as they say, there is no such thing as a "dumb" question other than the one that doesn't get asked. Scroll away, have fun and enjoy the ride. But be careful, it IS addicting.