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Old 05-20-2009, 06:07 PM
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Default geodesic dome enclosure

Things are moving along, taking a little time out from cutting brick to do some planning for the enclosure. I was originally planning a fairly traditional gable type enclosure but decided I wanted to keep the overall size of the oven as small as possible which led me to consider the "igloo" style. This is a mock-up of my current thinking, what I hope will eventually be a geodesic galvanized sheet metal enclosure (maybe copper)

I'd like to have a fairly water tight cover for the oven which this should accomplish, also, I think I'll be able to back fill with 3 or 4 inches of loose vermiculite over the 2 inches of blanket insulation I'll be using. I really like the look of many of the stucco domes out there, I'm just concerned that with our weather extremes here that the stucco will be hard to maintain or just may not hold up well.

I haven't come across any discussion of this type of self supporting enclosure, maybe there's a reason no one does this? (aside from all of the sheet metal work) Any thoughts would be greatly appreciated.

Holiday weekend coming, ready for 3 straight days of oven building!

Thanks, Doug




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Old 05-20-2009, 07:01 PM
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Default Re: geodesic dome enclosure

My oven is geodesic on the inside, not the outside. What material/finish are you planning?
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Old 05-21-2009, 08:59 AM
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Default Re: geodesic dome enclosure

I am thinking of using 26 or 24 ga galvanized sheet metal. ( still considering copper, I have to work out the yield for copper based on stock sizes, but my first guesstimate put the material cost alone at $400. or so! sure would look nice though)

The plan is for a self supporting dome, so I would cut the triangular parts with tabs turned inward that could be riveted from the inside and either soldered or caulked from the outside. I would leave a few panels loose until I had everything in place then backfill with the vermiculite and solder or caulk them in place. Not sure if I need to allow for any ventilation, but I'm considering that too, just so there aren't any condensation problems.

The mockup is corrugated polypropylene panel (recycled campaign signs) and it went together so quickly and was so sturdy with just some packaging tape holding it together that I was encouraged to keep figuring this out.

Lots of work to do still, just seems like a great application for a geodesic dome.

Doug
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Old 05-21-2009, 01:10 PM
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Default Re: geodesic dome enclosure

Doug,

It looks really cool. Did you leave room under the mock-up for insulation. Looks like pretty tight quarters from the photos.
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Old 05-21-2009, 01:30 PM
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Default Re: geodesic dome enclosure

The problem with the geodesic dome, going back to Buckminster Fuller, is leaks. I would engineer your metal panels so that they extend above the triangle above it, so that you have distinct overlapping, as one would with roofing or flashing. I would also keep your joints to a minimum, using large sheets to form the polygrams, with the angles bent in a brake. This is of course easier said than done.

Also remember that if you are using ruinously expensive copper, and planning to solder the panels together, you are going to want a method of flowing the joints without the solder running down the visible panels. A gunsmithing supply will have a homogenized soft solder that will simplify this job.

Good luck with this. Don't hesitate to talk to a sheet metal fabricator. They may have many good suggestions, and well as access to sheers and brakes that will make the job more professional looking.

BTW, galvanized and heat may not be a good combo. Go to the junkyard and look for scrap commercial kitchen stuff with sheets of stainless steel.
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Old 05-21-2009, 02:01 PM
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Default Re: geodesic dome enclosure

Thanks for the input:

Ken, the mockup is sagging a bit in the photos, but at the current size it has room for 2" of blanket and an additional 2" of vermiculite at the narrowest cross section, probably will scale it up an inch or so in diameter to get a bit more.

Dmun, all good points, I'm probably ruling out copper at this point, I have had reasonable luck soldering galvanized sheet, (although this is A LOT of soldering) I was assuming that with sufficient insulation the internal temperature of the enclosure wouldn't be a problem with the galvanized. I will have to look at the idea of 'shingling' the panels,

Thanks,

Doug
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Old 05-21-2009, 07:40 PM
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Default Re: geodesic dome enclosure

Doug,
This sheet metal stuff is my thing. Copper would be pretty easy to solder up. Since you can do your fab on the bench (off the oven) just vice grip your joints one at at time and turn the unit so the solder can only flow where you want it. Use 50/50 for very easy working and a liquid flux. You could even slosh water around to check it. If you can solder galvy this will be really easy. The outside won't get hot enough to de-solder anything. Can't wait to see it.

Mark

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Old 05-22-2009, 06:18 AM
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Default Re: geodesic dome enclosure

Mark, thanks for the encouragement and advice, I think I'll have a sheet metal shop cut the blanks and I'll do the bending myself, I have been thinking that copper would be easier to work with, I'm gonna play around with some joints in various material and see how it goes. Someone suggested something called "galvalume" but I think I'll have to silicone that rather than solder, I like the idea of soldering, and with your suggestion of clamping I think I can avoid having to screw or rivet each seam.

meanwhile....back to building that brick dome, starting to mortar tonight!

Thanks,

Doug
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Old 05-22-2009, 07:37 PM
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Default Re: geodesic dome enclosure

Doug, galvalume is nice stuff, lasts longer than straight Galv G90 but doesn't solder so well. Could be assembled with caulk successfully. If you do this (use metal) make sure it's either really tight (vapor travel) or the cavity should be very well vented. Passive venting requires a 4-1 ratio of intake to exhaust, so, for instance if you had a 3" vent at the top, you would need 12 square inches around the bottom. Metal roofs sweat a little on the inside on an almost daily basis if atmosphere enters.

Mark
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Old 05-22-2009, 07:57 PM
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Default Re: geodesic dome enclosure

I have to say I'm with dmun on this one... that's a lot of seams to seal, even if you make it out of folded polygons. If I were doing that large an area of rounded sheet metal, especially if I were going to the expense of copper, I would seriously consider hand-hammering it out of a single sheet. Copper works pretty easily, and you'd definitely have something eye-catching. Plus, no leaks. It sounds like a lot of work, but to my mind it's no worse than the meticulous seam work the dome would require, with the added peace of mind about water intrusion into the vermiculite and the potential for corrosion in trapped pockets.

At it's core, though, I'll admit to a bit of personal prejudice. Maybe it's extravagant, but I do love me some hammered copper. Outdoors on an oven it would turn that beautiful green fairly quickly. Also, I'm pretty confident in my hammerwork, which would admittedly make this a daunting task to someone whose never done much of it.

If you wanted to keep it simpler, you could do something kind of halfway between the two... a vertically-seamed dome (which would be less likely to catch and hold water in the seams) on a square (think Greenwich Observatory), hexagonal, or octagonal planform. That way you'd only have to curve the metal on one axis, but could still get some attractively architectural results.
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