Here are some details on my Van De Graaf generator:
It was built with a bench grinder engine with a Teflon bottom and Nylon top pulley. The ball is a garden stainless steel gazing ball and the belt is made of rubber.
Here is the source 3D image for Sketchup 3D Van de Graaf 3D Sketchup model
Here is a small video of the generator Van de Graaf video