You can remove the screw from the end of the little drum sander you get with your dremel tool. Replace screw with a piece of bevel sandpaper on the end of the little sanding drum. It works really well. The length of the sander attachemnt plus the mandrel gets to the bottom (or at least deep enough) of the hole. Also you can find a cutting disk tool for the dremel. Replace the cutting wheel with your bevel sandpaper. That work ok to.