Any Van de Graaff generator experts in here?

[f150trk21]

I got most of the parts but not sure on the design. All the ones I've seen online have a large hole cut into the bottom of the sphere with the top pulley inside the sphere. I can't find any information that this in necessary. For ease on construction I thought I'd put the top pulley under the sphere in the support tube and run a wire from the comb to the inside of the sphere. Im going to try this idea this weekend, but wanted some input if I'm going the right direction.

thanks
Jason

vandegraaff.jpg

[Vidal Wolf]

give it a shot and let us know how it works out.
-Nate.

[DanBarlow]

Electrostatics is fun! If you were East you could visit the Doctor's original generators at the Boston Museum of Science, they built a three story hall just for the display.
The reason the takeoff is inside the top ball is so there's no electric field keeping the electrons from coming off the belt.
All the electrons are gathering on the outside surface of the ball since they repel each other.
If the takeoff is outside the ball, the electrons on the belt will also be repelled and won't build up anywhere near as much voltage.
If the takeoff is inside the ball, the effective local voltage is zero and the electrons will keep coming off the belt until the air breaks down.
In the case of the original, that's a 17 foot spark.

[f150trk21]

Thanks Dan

That makes more sense. Guess I'll need to figure out how to cut a 4" hole in one of the bowls. I'll post the progress.

[absolom7691]

Guess I'll need to figure out how to cut a 4" hole in one of the bowls.

I would think a plasma cutter would work well. Make your initial cut and then clean it up with a file and "polish" with different grit sand paper.

[lasersbee]

A Dremel tool with a disk cutting blade may work.
Or if the bowls are too large you can use a Die Grinder
or Cut Off Grinder.

Jerry

[buffo]

Why not use a 4" hole saw? Stick it on the end of a drill and you're done in less than a minute.

Here's a link to Home Depot, but I'm sure you can get one cheaper...

Adam

Edit: Here's one for $11.

[kecked]

Try a diamond hole saw. They sell them for cutting glass in fishtanks.
http://www.bulkreefsupply.com/diamon...rill-bits.html

The take off has to be inside for it to work. The charge builds up on the outside.
The inside is a gauss cage with zero potential.
If you want to really make it fly pull a vacuum inside the system.

The ball can be made of almost anything. You can use a plastic ball covered in copper tape.
You just need to make the top surface contact the inside by coating both side of the sphere and outside.
IE tape both the inside and outside. Use the copper tape used for shielding guitars.
I have not tried this but is sounds reasonable. It is only the surface that counts.

http://www.stewmac.com/Pickups_and_E...All%20Products

I prefer the whimshurst for electrostatics.

[turbohead]

Here is a site that shows the construction of a Van de Graaff generator and using a Dremel to cut the hole in the metal sphere:

http://mark.rehorst.com/Van_de_Graaff/

I would not recommend a hole saw from Home Depot since the teeth are too coarse.

[f150trk21]

Thanks for the suggestions. After some measuring, I'll need a 4.75" hole and the bowl is stainless steel. I briefly tried a dremel with cutting wheel, but that would be very slow going and my bad hands aren't up to it. I do have a 10" drill press but it seems risky to put a 4.75" hole saw on it. Maybe I can find a machine shop that'll do it.

thank
Jason