Introduction: Armillary Fusor
Fusion! Based generally on the Make article (http://makezine.com/projects/make-36-boards/nuclear-fusor/) this is a demonstration fusor housed inside a replica armillary sphere.
Step 1: The Chamber
The brass blanks were cut from 3/8" brass sheet with a hole saw. The stepped shape of the top cover is from my initial (smaller) hole saw breaking off at the shank halfway through. This proved fortuitous, not just because the stepped shape looks cool but because it otherwise would have been too small.
To remove tool marks and round the edges I put a bolt through the center hole and put that in the chuck of a drill press. Files held against the rotation of the brass reshaped the edges, followed by sandpaper and finally polishing compound.
The tapped holes were cut to 1/8" NPT. Fun fact - lamps use NPT threads, meaning you can use lamp parts with plumbing fixtures. The right angle bit attaching the vacuum gauge is from an old chandelier.
The standoffs are bits of stainless rod I threaded in the drill press. Don't turn the press on, just use it as a jig to get the tap started to keep things square.
The cage is soldered stainless steel wire. My first version was silicon bronze MIG wire but that couldn't take the heat and began falling apart. If you're having trouble soldering stainless you need to use the proper FLUX. Not rosin or high temp brazing flux, low temp liquid flux for soft solder. Harris stay-clean is cheap and readily available and makes soldering stainless a breeze.
The feedthrough is a standoff epoxied into a ceramic rod. If I were to do something different it would be to run the ceramic all the way to the top but this works.
Step 2: Variac, Transformer and Rectifier
In the first picture you can see the transformer, rectifier and the bottom of the VU meters visible from the top.
The transformer is a 10KV oil burner ignition transformer. I could get a used one cheaply from a hvac plumbing supply house near where I live but it's a little underpowered - I hope to replace it with a 15kv neon sign transformer I found on the street a few days ago.
The rectifier is in the grey box on the side of the transformer - two opposing diodes in a container filled with mineral oil. The Make article suggested using a plumbing T but I found that to be cumbersome and kind of ugly, here I used a salvaged parts enclosure sealed with epoxy.
The variac is one I picked up on ebay and I'm not the first person to take the poor thing apart - guessing by the hand drawn schematic I found inside someone in the 50s or 60s hacked a normal variac into this enclosure. The face is random sheet metal covering separate holes for other components. It worked out well - the box holds everything I need and seals for easy transportation.
The LEDs under the VU meters are blinking leds connected in parallel to cause to the VU meters to dance. As the leds blink in and out of synch it causes the meter (which is basically just a carefully calibrated ammeter) to bounce at different intensities. It adds a lot of animation to the final product, I'm pleased with the solution.
Step 3: Control Box
Built from some sort of vacuum tube testing equipment I found in an abandoned coat factory, this is basically just a dressed up box to hold switches. The transformer in the bottom right powers all the blinking LEDs, the switches on the left control the variac, pump and transformer and the outlet in back runs to the pump.
One interesting challenge was using a 12vdc light up switch to run 120v power. I pried the switch apart, ran seperate wires to the red LED in the body of the switch and put it back together to isolate the switch and LED. Works like a charm and was easier than I expected.
Step 4: Retrospective
The vacuum is insufficient to get the full effect of the fusor but I wanted to share while there was still time. I plan on continuing to tinker until I can get a real star-in-a-jar going but until then I'm still pleased with the final result.