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toroid construction

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LAN_403

GreySoul

Tue May 15 2007, 08:52PM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

Firkragg, good point. the commercial 2-part polyurethane foams for shipping/insulation seem to expand and cure in a sealed package just fine... the problem I had was with DAP foam and Great Stuff brands...I thought they were the same stuff, but I was told by someone at the time they weren't.

-Doug

Tetrafluoroethane

Wed May 16 2007, 12:31PM

Registered Member #127 Joined: Fri Feb 10 2006, 03:36PM
Location: Cincinnati, OH - USA
Posts: 44

I also have had great success with the stacked & carved foam. I even had the home improvement store I bought it from cut it for me (24" sqares). For the stacking I used spray adhesive, but anything that won't eat the foam should work. Shaping was done by hand with a wood rasp and sandpaper. I just used Al tape on mine, but it works very well. I never had a problem with heating, but then I never tried to run my coil on over 900 watts. Though I have run it continuously for extended periods though (about 30 min).

Kristian

Fri May 18 2007, 08:47AM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

Hi all, I took a break from the topload construction for a while. I've been going down to the Geek Group headquarters for the past few weekends and getting some help and advice on other aspects of my project. Their willingness to help is amazing.

Anyway, I'm back at the topload creation. I'm about to attempt to cover the pool toy with paper mache. Parts Scavenger, that idea brought me back to when I was a kid and would cover balloons in paper mache. Once it hardened, you could pop the ballon and the paper mache would keep its form. The pool toy is a balloon. Perfect! (I hope)

I was thinking that once it is dry, I would put a few coats of poly on it to smooth it out a bit. It should be fairly durable. Then I'll cover it in al tape or foil.

Could any of you guys that have done the aluminum foil with success post more details on the process? I would like to have this done by noon on Saturday. I'm running out of time and I have so much to complete before the Tesla-thon June 2.

Reaching

Fri May 18 2007, 08:57AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

I use the aluminium duct that you get in your local store and fill it up with this 2 component cement you use for a car. then i smooth it all with sandpaper to get a clean surface. an then i tape the alu on it.

this works fine but you need much time to get it right

Part Scavenger

Fri May 18 2007, 12:21PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

I'm on my break @ work right now... I'll see what I can dig up when I get home, but it's pretty much the same as I did with the bottle caps on my site. Only, I cut the Al foil (just regular kitchen foil) into 1" strips, sprayed it with contact cement (shiny side out), let it get tacky, and applied. You want to attach the foil right in the middle of the foil and on the outer rim of the toroid. This makes sure the strips overlap correctly. I overlap about 1/4 on the rim, but by the time it makes it to the center, it's almost 3/4. Smooth down with your fingers, then roll with the wallpaper roller or a spoon or something. Careful with the spoon, it tends to tear the foil. Then get a piece of cardboard or something, cut it round, cover it with foil, and glue it in the top to cover up all the ends...

I think I've got some pics when I get home.

Cain

Thu May 24 2007, 02:19PM

Registered Member #624 Joined: Tue Apr 03 2007, 07:50AM
Location:
Posts: 59

I'm currently making a toroid out of 6 inch ducting that i have covered in the expanding foam and am now carving it down.. i am thinking about trying to turn it... its in the early stages at the moment, but here she is:

Ken M.

Fri May 25 2007, 12:50AM

Registered Member #618 Joined: Sat Mar 31 2007, 04:15AM
Location: Us-Great Lakes
Posts: 628

Mmmmmm Looks like a giant glazed donut! Looks pretty for early stages, is it working out, as in easy to craft, light weight?

Cain

Fri May 25 2007, 04:28PM

Registered Member #624 Joined: Tue Apr 03 2007, 07:50AM
Location:
Posts: 59

yeah very light weight...

and you can use the cheap light weight ducting...

but i used 2 cans of foam on her so far and still have a few small gaps.. but i think i will use an epoxy filler to patch..

as for sculpting..

i have used a long bladed knife so far with great ease, although getting it nice and round will be the challenge, smooth will be easy but nice and even wont be..

i am thinking i might try using an electric plane on her while i rotate it in a lathe ( you could use a drill in a vice i suppose)

Part Scavenger

Fri May 25 2007, 11:21PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Tip: A coarse wood rasp works great for shaping foam toroids on the lathe.

Kristian

Sat Jun 16 2007, 04:50PM

Registered Member #611 Joined: Wed Mar 28 2007, 11:40PM
Location: Hudsonville, Michigan
Posts: 79

The pool toy I was trying to wrap didn't work out. The plastic expanded over time and pulled the paper mache off. I have since decided to go with a stacked toroid design. I finally wound the secondary. I picked up what was supposed to be 1500 feet of 26 gauge. What came in the mail was only 1lb. I came up a little short. I was hoping to get 22.5 inches of winding on a 4.5 inch form. I only got 19.75 inches of winding. The form itself is 36 inches long, and needs to be cut down to size yet.

The power is 15KV, 60mA NST. The capacitor is 20KV, .015uf. The primary is 15 turns of .25 inch copper tube with .25 spacing in between turns and 1.5 inch spacing between primary and secondary. I need help with the toroid dimensions. My idea for the top load is to wrap 4 inch aluminum duct around the bottom of a flower pot and 6 inch duct around the top. This will give me two stacked toroids. The dimensions are 4" minor, 15.25" major for the bottom toroid and 6"minor, 22.25" major for the top. There is 7.5" in between the center hights. Does this sound about right, size wise?

I was also wondering if anyone had any advise for how high up from the top of the secondary winding I should place this? I will be able to adjust it up to 2 inches up or down on the bolt that it will mount to. Would 2 inches from the top turn to the bottom of the toroid, with the option of going up or down 1 inch, work? Does this give me enough room to play with? Any advice on this would be great help.

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