■ FIGURE 4.
Top Roller and Brushes
Figure 5 shows the top roller and brush. For my top
roller, I used an old bicycle hub being tossed out at the
bike shop. Ideally, it would be nice to use a bike hub
with sealed bearings. Because a bike hub spins vastly
faster in a Van de Graaff than it was designed to on a
bike, if there is any light oil inside, it will be spun out and
entirely ruin your Van de Graaff belt.
Important note: Any oil at all in your Van de Graaff
should be avoided! The
electrostatic charge will attract
the oil to the belt, ruin the belt,
and contaminate the rollers.
I found my top high potential spherical terminal at
Walmart, where it had been mislabeled as a “piggy
bank.” (You can see the coin slot
they mistakenly put in the top.)
These pop up from time to time
and are worth looking for, though
it seems to be a seasonal or
promotional item for them. If you
hunt around, you’re sure to find
other objects that will work.
In the past, I’ve used two
stainless steel bowls (available
everywhere) face to face to form
an excellent and durable sphere. If
you do this, be sure to coat all the
sharp edges of the bowl with
several heavy coats of corona
dope, including the hole you cut to
accept the Van de Graaff column
before assembling. The easiest way
to cut a large hole in a metal
sphere is with a Dremel tool and
cut-off disk; then, file and sand the
hole to perfection.
■ FIGURE 5.