I'm a member of that same group; just saw your post there.
That project is a really novel idea. Just need to get off my butt and work on my entry...
And if I may --
Question: what is the difference from a 'mechanical pencil' to graphite ones? (See how untrained I am!!)
Mechanical pencils are the "pump lead" ones, usually made of plastic. Most of them are #2/HB, but I'm seeing the other lead weights put into mechanical pencils, too. They're just not the traditional wood, "sharpen me up" pencils!