900,000 volt Van de Graaff Generator Using Cheap Parts

Step 17 Sphere

Use a Dremel tool with a good cutting disk and cut a 4.5 inch hole your sphere and make sure it fits.
Take your time and cut slowly, the woven carbide disks worked best.

The first time I fired mine up it worked but had allot of sparks jumping from the bottom of the sphere, to solve or help this problem I fitted a copper ring for the sphere to sit on. This will fold the charge back up to it. If you dont have a pipe bender tape one end of the pipe shut, fill it with water and freeze it that way you wont kink it wile hand bending it.

After I got the copper ring bent in a circle I cut it and clamped it, so it could be soldered with the torch

I also cut several more 1/2 inch tall rings off the coupler and put them on the column, this keeps the voltage from creeping down.

Also make the sphere sit as high on the column as you can without losing contact with the comb inside, my sphere is around 4" down the column.

Comments

[methoxypropyl]

I have found that you can make rings or coils very nicely by first filling the tube/pipe with sand. You must make sure there are no cavities otherwise the walls will collapse in very small diameter rings or coils. This has been an extremely effective way to make cooling coils for the technology I work in. Also make sure the sand is contained to prevent it falling out. Moonshine anyone?

[florinandrei]

What was exactly the diameter of the copper ring, compared to the hole in the steel ball?

I mean, where was the edge of the hole, in relation to the uppermost part of the copper ring? Was it inside (so the ring is kind of "surrounding" the hole)? Was it outside? Was it so the edge of the hole is sitting exactly on the top of the ring?

[nickademuss]

The sphere's hole is just large enough to fit over the pipe, the copper ring was wrapped around the same pipe, so the inside diameter of the copper tube is the same as the outside diameter of the pipe.

[marcfiam]

I don't know the specific answer for the model in this instructable, but in general in Van de Graafs you want to minimize all what is a proeminent edges, as electrical charges leave from any sharp or small radius conducting element.
This is why in my model I moved the support of the ball inside the sphere to avoid electrical losses.

[bobslau]

Copper pipe is sold by nominal sizes which are not the actual sizes.  Did you use 3/4" nominal which is actually 0.875 outside diameter, or 1/2" nominal which is actually 0.625 outside diameter?

Also, there is hard copper pipe, which is very hard to bend, and soft copper pipe, which  is easy to bend.  I had a hard time finding the soft per foot (a standard roll is over $100), but finally found it at http://www.statesupply.com/displayCategory.do?Id=2223.

[nickademuss]

I used the soft 3/4"  pipe,  The larger the diameter the beter, just harder to bend. Thanks for posting the site.

[rmelchiori]

Could you use copper tubing instead of copper pipe?  Tubing comes in a roll and is very easy to bend.

[nickademuss]

yep

[bobslau]

Yes.  I call copper tubing soft copper pipe.  You can only bend the pipe (hard pipe with great effort and then it kinks.

[Syncopator]

A cousin who worked as an apprentice at a famous British engineering company http://www.localhistory.scit.wlv.ac.uk/Museum/Engineering/JohnThompson/johnthompson00.htm#menu asked me if I knew the difference between a pipe and a tube.  He was taught that one was rolled and therefore had a seam, the other is drawn and therefore doesn't have a seam.  I can't remember now which is which.  
Apparently this basic distinction is no longer taught or passed on.  The result is that there is great confusion and no one knows the facts any more.                                                 

[nickademuss]

Hmm, good idea, It was a pain in the rear to do it the way I did. Oh well live and learn....

[malsa]

hi
i am confused about where the negative charge comes from and do you make a hole in the sphere for the copper wire to come through and how and how and why do you do step 17?

[nickademuss]

The charge is dragged from the earth ground by the constant belt movement, step 17 is done to prevent leakage of the high voltage.

High voltage will run to any raised part or lip on the sphere and cast off to the air.

[Electrik]

How would i bend the pipe so it is a circle? Should i bend it around something?

[nickademuss]

I filled mine with water and froze it so it would not kink then, bent it around the pipe it was going on. Be sure to use much more pipe than is needed for extra leverage.

[Electrik]

Okay _{Thanx =]}