Of course, large production shops have expensive machinery that will sand moulding. For the smaller woodworker, however, there is an easy and basic technique for sanding by hand.
Take a piece of the molding and glue some 80 grit sandpaper to it. Then take some foam insulation board and rub it over the profile, allowing the sandpaper to shape the foam board, creating a reverse pattern.
Once complete, glue a piece of sandpaper (now in the proper grit for finishing) to your new foam board sanding block!
For information on sandpaper sheets that you could use, check out our website at: www.abrasiveresource.com