This video shows how to make a camera setup for filming what you're doing on a table. It's a great video even if you don't intend to make one, but if you're trying to teach someone how to do something, this is an awesome setup. Either way, it's entertaining to watch.
The creator, Paco Warabi, says:
"It allows you to film directly downwards, which works pretty well for filming knot-tying. But then my wife wanted to digitize some artwork that wouldn't fit in the scanner, and we discovered that the Knot Demonstrator works for that, too.
So after a lot of experimentation and changes, I've come up with a stable design that allows you to film and photograph anything from directly above. The new name is Tabletop Demonstrator because it can be used for much more than just knot videos."
A material list and diagram for building your own are available on his website.