WARNING: Keep the VDG away from all electronics, including pacemakers, hearing aids, and the cell phone you forgot was in your pocket. A VDG is an ESD monster!
Step 1: Materials and Tools
 3/4" Schedule 40 PVC pipe
 3/4" PVC Tee
 3/4" PVC Cap
 3 1/2" x 1/4" Rubber bands (No. 64)
 Super Glue
 Hot Glue
 3 ft 16 AWG Stranded Wire (can be taken from old extension cord)
 Motor (like Radio Shack #273-223)
 4xAA Battery Holder (like Radio Shack #270-391)
 Wooden Dowel
 Aluminum Foil
 Aluminum Can
 Wide-mouth Plastic Bottle like a 32 oz Gatorade bottle
 Paper clip
 polyvinyl chloride electrical tape (Scotch 3M 33+ and 35 both work)
 Teflon tape
 glass bead [url:http://www.artbeads.com/czech-glass-rondelle-9mm.html]
Drill or Lighter, Nail, and Screw
Hot Glue Gun
Alligator Lead or Stiff Wire hooked at the end
Before starting, wash your hands and prepare a clean work area. The three enemies of a VDG are oil, water, and dirt. Therefore you should clean and thoroughly dry every part before construction. Use nonsoapy water only since soap can leave a conductive film. Before touching the rollers or belt wipe your hands to remove any excess oil.
Step 2: Motor and Bottom Roller
To create the bottom roller, cut a narrow strip of polyvinyl chloride electrical tape and wrap it around the motor's shaft. The best way to get the tape to wrap around the shaft is by pinching the tape to the shaft and rolling it between your thumb and index finger. You also want to crown the roller (make it thicker in the middle) by pulling your index finger slightly to the right for a couple turns then pushing back to the left for a couple more turns repeatedly as you roll on the tape. A crowned roller will keep the rubber band from slipping off the roller. Add a bit of super glue to the end of the tape strip to prevent it from unrolling, also add a little super glue to the edge of the roller to bind all the layers of tape together. I tried making rollers out of Teflon tape and silicone rubber, both of which are lower on the triboelectric series, but a roller made from electrical tape was easiest to work with. I did not know what material the generic black electrical tape I had was made from, so to be positive the bottom roller was vinyl electrical tape I used blue 3M 35, but 33+ should work well too.
Step 3: Bottom Comb and Battery Holder
The Radio Shack motor is meant to run at 1.5-3V, but if you use rechargeable batteries you can run the motor at 3.6V without too much trouble. A higher motor voltage causes the motor to turn at a higher RPM which results in more HV at the collector. I didn't have a 3xAA battery holder so I made a dummy battery out of a piece of wooden dowel cut to the same length as a AA, wrapped that in aluminum foil and insulated the sides with electrical tape. Hot glue the battery holder to the side of the Tee.
The Radio Shack motor has very thin brushes and lacks in construction quality. It gets the job done, but I'm positive there is a better motor out there waiting to take its place. Suggestions for a new motor a more than welcome.
Step 4: Belt
Too little glue is better than too much. Even if the bond doesn't occur along the entire edge, you can still see what the proper bond should look like before trying again.
Don't be afraid to mess up. The bound sets quickly, so you know right away whether the result is any good, and if it's not just trim the ends and try again.
You should use brand new rubber bands; old dirty rubber bands aren't worth the trouble.
Step 5: Column, Upper Roller, and Collector
The upper roller is a 9x6 mm roundelle Czech glass bead purchased from artbeads.com. Artbeads.com has no minimum order with free shipping, but please don't take advantage of them by spending less than a dollar; buy a few beads. The axis for the roller is made from a paper clip that has been straightened and formed into an L shape. Stick the paper clip through the holes in the column and trim the excess. Now curve the axel inward slightly. Wrap a little Teflon tape around the axel, and slip the bead over it. The slippery Teflon tape will prevent the paper clip from grinding the bead. Now tape two narrow strips of electrical tape on either side of the bead. You can use a wire stripper to cut away excess tape. These bumpers keep the bead from sliding to the left or right on the axel when you wave the VDG around. The holes in the column are of course too small to pass the bead and bumpers, so you must insert the assembly in the end of the PVC, hook the bottom of the L into one hole, then push the other end of the axel into the other hole.
To make the upper comb, cut 8 in of wire, strip 0.25 in from one end, which will be the upper comb, and 1 in from the other. Shape the wire around the column like the picture shows, then tape the wire to the column. Spread out the comb's strands and twist together the strands on the other end. The comb points at the roller when the generator is running, but can be easily moved out of the way to remove the upper roller assembly.
The collector is made of an aluminum can with the lid removed. First remove the can's tab. The aluminum can's lid can be cut out with a sharp knife but using a handheld can opener is much safer and leaves fewer sharp edges. Use a paper napkin to keep the wheel with teeth from puncturing the can. The can opener should be used like scissors to remove the lid; don't twist. The collector's support is made from a Gatorade or similar bottle. Trace the circumference of a piece of PVC onto the bottles lid. Remove the material from the lid within the circle. Place the aluminum can onto the bottle and trace a circle around the bottle where its neck meets the can. Cut the neck off the bottle using the line as reference. Don't cut exactly on the line, but leave a little excess, which can be trimmed away later if necessary. Screw the lid back onto the neck of the bottle and insert it onto the column starting from the bottom.
Step 6: Complete Assembly
To prevent the VDG from producing sparks you can cover the collector with a piece of cardboard. The VDG will still perform most of the same stunts including the merciless destruction of electronic devices.
Step 7: Fiddling and Debugging
Don't lose heart.
If you apply power to the motor and it doesn't turn, remove power immediately.
Attach a thin strip of toilet paper to the collector. As the collector charges, the tissue paper will rise. If you've got things working well, it will rise quickly and point almost straight up. You can also get a good idea how well the collector is charging by holding it close your ear. You will feel a stronger pull on the tiny hairs on your ear as well as hear more static crackles and pops when the VDG is working well.
If the rubber band is too tight the motor will not turn or turn slowly. Push the column further into the Tee or remove a bit of PVC from the end of the column.
If the rubber band is too loose it will make poor contact with the rollers and not turn it as fast as it could. If the rubber band slaps around pull the column out of the Tee a little. If the column is way too short you'll have to cut another longer one.
Make sure the combs aren't touching the belt. The combs should be about an eightth of an inch from the belt. Remember you didn't tape down the bottom comb so you could adjust it; once you've found the optimal distance secure it.
Van de Graaff generators will fail to work when the air is very humid. Use a hair dryer to blow out any moisture from inside the VDG.
Make sure you're touching the ground wire when you hold the handle.
When not using your VDG, unhook the rubber band so it doesn't deform and lose its elasticity.
Taping the bottle neck to the collector along with some extra tape on the bottom of the collector will help prevent losses due to brush discharge.
If you use an ohmeter to test the resistance of the inside of the can, you'll see that it has a nonconductive coating. The coating makes little difference at the high voltage a Van de Graaff generator produces, so don't bother scraping the coating off the can.
Step 8: FUN
Ring Franklin's bells. I like to set up Franklin's bells without a grounding wire; normally the can on the right in the video below would be grounded. Without the grounding wire the tab/clapper transfers charge between the cans until both cans are at the same voltage as the VDG. Then one can turn off the VDG, set it aside, and then discharge the second can; lo and behold, the bells start ringing again as if by magic.
Cause an incandescent light bulb to flash a violet-blue. A burnt out bulb works fine. Cover the glass with some clear tape to prevent shattering if the glass breaks.
Bend a thin stream of water.
Deflect soap bubbles.
Light a small neon bulb.
Stick paper to a wall.
Levitate Fun Fly Stick fliers.
Check out Prof. Bunsen's Fun Fly Stick video for various demostrations of a handheld VDG's powers.
Bill Beaty's website describes some other interesting VDG stunts.
Giving a shock to someone who isn't expecting it sounds like good fun, but it's a bad idea. Though the current and pain will be minimal, the surprise of the shock could cause a person to jump back reflexively and hurt themselves. It's also possible you could destroy an expensive or essential electronic device they have on them.
You can make a CFL bulb glow, but you probably shouldn't. Once I was making a CFL glow while holding it in my hand when I received a shock much brighter, louder, and more painful than anything I've received from the VDG by itself. Unlike an ordinary fluorescent tube a CFL has an integrated starter and ballast. This circuitry contains capacitors which will charge slowly from the VDG, but will release that charge all at once with the result being a higher current and a bigger shock. If the shock doesn't harm you, the surprise of it could cause you to drop the bulb releasing mercury and broken glass into your surroundings.
Never charge a capacitor with a VDG unless you understand the risks involved. A VDG is a high voltage but very low current device. A capacitor can have high voltage and supply a potentially deadly current.