I rec'd a series of photos the other day that were interesting for a couple of reasons. First, the oven has a really nice pure-brick finish that looks great. Also, the builder used collapsible forms to keep a consistent inward curve.
Take a look at:
That is a good way to keep your curve consistent.
In his picture he shows 4 vanes on his form. I do the same thing except I use a single vane.
I find exact center for the dome and mark it. I then rotate the vane around the the center as I lay each brick.this lets me stay very accurate with my chains.
I was thinking of using a stiff foam board that I could break out at the last minute.
The multiple vanes allows the form to be more stable I would think than a single vane. Very nice solution. How do they collapse out?
Using foam board (2" insulation board) would make a very nice form and is easily broken out when the time comes to pull it from the oven. The board is usually available in 2' widths so it wouldn't be a problem to do up to a 48" oven without having to pin a couple of boards together.
This is similar to my sand form concept (using a dowel in the center with an arch curved vane to smooth the sand pile into the proper shape before beginning the arch). All of these forms will make the construction a bit easier as the builder won't need to rely on the mortar to hold the bricks to the ring while building. Be easier on the upper reaches too where until the last one is in, it doesn't lock and you need a helper or a form to keep the rings in place.
Last courses of the dome have many different approaches
(M) Dear Luis,
(M) I have ready of many different ways to support the dome during construction. Each method seems to have it's adherants.
(M) You, Luis "build the dome using 16 polystyrene vanes in place of 4 like our friend jcdup did"
(M) Some like Keith, below
[QUOTE=Keith Oertli]"That is a good way to keep your curve consistent.
In his picture he shows 4 vanes on his form. I do the same thing except I use a single vane."
(K.O.) I find exact center for the dome and mark it. I then rotate the vane around the the center as I lay each brick.this lets me stay very accurate with my chains."
(M) I did a Search on this Forum for "Vanes" and found so many entries that I couldn't read them all. I have read a view, expressed I believe by either Jim, or James, that having fewer vanes allows the builder to see inside the dome as s/he builds. Fewer vanes may also allow for an easier rotation, but many vanes provide stability. I don't know where to find a middle ground ???
(M) I hope to pour the foundation slab tomorrow so I am too far away to make any intelligent suggestion. But after reading all these views I do have a question:
(M) If I use a "Lazy Susan" (a plate that rotates on a bearing ring) and choose one that will pass through the neck-entry of the "igloo", would it be significantly easier to rotate the vanes whether I use 1, 4 or 16 vanes ? _____
(M) At "Jerry's", my Home Center, they offer a denser foam board. It is not solid insulation. It is pink and about twice the cost of the white styrene but still only $6 for a 4x8 sheet. Unless I hear from more experienced builders that using this material is a mistake, I plan to use it. I figure that if I go with fewer vanes (probably 4?) that the pink foam will be less likely to break during construction. Comments? ______
personally i think the 16 vane method works great, though indeed you cannot clean as easily as you work. the major advantage--and the point where it is hardest to clean--is when you get to the top, and you already have forms in place when gravity takes over. i'm a bit of a perfectionist, and so i was annoyed at the random bits of mortar hanging into the dome in the top after i pulled my forms out, but i just tapped the excess loose with a hammer before i fired it and you know, you'd never know the difference.
I'd use Paul's multivane, or the wire loops
I just finished my oven and didn't have the advantage of all of Paul's great ideas ahead of time. I set the few few rows with only the single vane as a guide for the curvature of the dome and they looked great. Of course, when I realized I would need some sort of support as I began to "turn the corner" moving upward, it was too late to place the nice one Paul had been using. (He was about two days behind me on the build, I think.)
At any rate, I had to be a little more creative than I wanted to and came up with a similar solution, though not as pretty. I'm happy to say that it all held and I am a happy man!
One suggestion for those in the building process: Take the time to use a masonry blade on an angle grinder, and start tapering the edges of the bricks at the point that the gaps begin to open up on the inside surfaces. I began doing it on about row 6, which really closed up the gaps and made for a cleaner, smoother and stronger dome. I would definitely have begun it earlier.
Good luck to you, and enjoy!
great advice about tapering the edges! on row 10 or so, i actually trapezoided (just randomly cutting actually) every brick, and they fit together really snuggly. if you are using a 10" wet saw, i would go a little bit further and use a bit of jim's engineering (in another thread), and cut every brick like that. the gaps really open up towards the top, and those last few triangular keystones are really kind of a pain in the ass. it would be nice for it to just close in properly at the top, but would require a bit of thought to execute.
Tight fit is worth it
I was very careful with the last several pieces. I wanted them to be very snug as they would be the final sources of strength.
I surprised myself by cutting them so carefully that I could not fit any mortar between the last 6 or 7 pieces. When I had a 12" circle open at the top I careful cut them like puzzle pieces to dry fit, then ended up tapping them in carefully together into playce with the rubber mallet. It was simply too close to fit any other way. Then I forced a little morter into the small joints on top.
I immediately removed the support vanes, to make sure I fixed it before any mud stiffened up. I found it was strong and tight enough to put significant pressure on the top of the dome without anything budging.
I was a happy man! :D
Humor in a jugular vane with Lazy Susan
(M) A few weeks ago I posted the following question but got no input regarding the "Lazy Susan""
"(M) If I use a "Lazy Susan" (a plate that rotates on a bearing ring) and choose one that will pass through the neck-entry of the "igloo", would it be significantly easier to rotate the vanes whether I use 1, 4 or 16 vanes ? _____"
(M) Now that I've read some more posts I am begining to doubt that I could usefully employ the 12" diameter "Lazy Susan" for my 42" dome (except perhaps if I used only one (1) vane) and I'm reluctant to do that despite the success of one builder with that approach.
(M) Am I wasting my time even considering a Lazy Susan for turning the vanes during the construction of the dome? ___
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