The upper side of the sandal is sanded with a high-speed disk, removing the ridges between the tracks cut by the router and generally smoothing things out. The high-speed grinder is quite hard to control, so it is important not to allow it to remove too much material. Following the initial sanding, I repeated with a slower-speed disk (disk mounted in a variable-speed electric drill), and finished by hand with a medium-grit sandpaper.
There is a vacuum set up to one side of the work, with a large funnel to try and catch the dust. It was only partly successful. This sander makes a lot of very fine dust that gets on everything. It would be better to do this outdoors, or in some kind of booth where the dust can be better controlled.