80cm dome, air chamber space

[Lucag]

Hello! I did not have a lot of success designing a plan so I have decided to simulate it with bricks first and going back to the plan when I find something that works for me!
I have learn so much in these two months and cannot wait to start, but I am still without a solid construction plan.

I am really committed to make the 80cm diameter fit in my 137cm base, and to use bricks instead of casting.
I can consider casting the cimeney.

I would like a feedback on these dimensions for the smoke chamber / arcs, I know I am stretching the cord here.

My smoke chamber will rest on:
- the last 4cm of the internal arc
- the external arc will have a base of just 7cm.

Do you think it will work ?

[UtahBeehiver]

Here is a pic of the first course of a tapered arch, cut from a full brick, notice how the follows the arc of the ID of the dome.

[Lucag]

There is still hope then! Please see this quick edit from my previous plan.

1) inner arch is now full brick width
2) rear arch is gone

does it work in your opinion ?
this is for 70cm diameter but it feels like I can probably stretch it to 75cm tonight if I redraw everything

[UtahBeehiver]

JR is correct on my suggestion of needing more than 1/2 bricks on tapered inner arches which I referred to in original post. This is what is shown on the pic.

[JRPizza]

As I said, you should get David to weigh in on the proper pipe size, but 1.5 bricks should be plenty for a vent length. I may be wrong, but I think Russell was saying that 1/2 brick is/maybe too short at the bottom layer to make a proper inner arch, not that 1.5 will not make a satisfactory vent. Back before I started my build thread, I had a thread on hearth size where there is good discussion on placing the inner arch (linked below). You can see by the end of the thread I realized that there are a few inches where you can move the arch forward or back and still have the bricks tie in nicely, where rearward will move the vent closer to the dome and forward gives more oven internal space. I don't recall if you are going to try to build a hemispherical arch or a flat one, but all of my layouts were done with the former.
Edit: I see you have figured out your pipe size, which should be plenty large for the oven you are planning. With a 1.5 brick vent you will end up with a rectangular opening that you will need to transition to square if you use a standard adapter. If you build yours similar to how I did mine you should have plenty of room.

[Lucag]

Hi JRpizza, I see your post only now! I am based in London and I can find almost anything locally. Initial idea for the cimney was to go up with bricks and then 15cm pipe. I am open to anything that works for my case, do you have any suggestion? Thank you again for your help you guys are really a great community!

[david s]

You really need to do that accurate scale drawing of the side elevation.

[Lucag]

Well I can buy any brick size or cut them any size I want for best result For the dome I was planning to use 23 x 11 x 6.4cm
11cm will be the thickness of the dome.

what really puzzle me is why 1.5 bricks lenght for the entry are not enough in my case, and what is the correct measurement I should use. I am really keen on using bricks, using a diameter from 70cm to 80cm depending on available space, but is hard for me to do any progress because I don’t know what I am aiming for, like the ideal dimensions for my entry

[JRPizza]

Lucag, building a non-standard oven almost requires figuring out every detail before you start, as you begin with multiple possibilities but every decision you make starts to constrain what you can do in the following steps.
Do you know what you are going to use for a chimney? I would ask a smaller oven expert like David what size chimney you need to avoid smoke coming out the front of your oven. I don't know if you could go down to the equivalent of a 4" pipe, and don't know what sizes you can obtain locally. Then you need to decide if you want to use masonry or steel pipe, and if steel do you want/need double wall pipe (are you going through a roof or does code necessitate double wall)? Knowing pipe diameter will tell you the area of the pipe and help you figure out the minimum opening.
I attached a picture of a vent design where I believe the inner arch is incorporated into the vent, allowing the vent to be much shorter. I can't remember if he was able to design a reveal into the vent so the door could rest against the inner arch, but it does show how you can shorten a vent. The builder was Amac and I put in a link to his build. His was one of the many I borrowed ideas from. Here is a link to his build
https://community.fornobravo.com/for...argate-pompeii

[david s]

If building with brick units the dimensions are largely determined by the size of the bricks and how they can be arranged. Apart from casting there is a third option and that is to build the flue gallery from sheet metal. You can have brick sides with a sheet metal form placed on top. An inverted funnel is simple enough, although compound curves are difficult. The material needs to be on corrosive, probably stainless steel or copper would be the most suitable.

[Lucag]

Thanks David, So far this seems to be my best option: I can cast the whole entrance and have the cimeney near the entrance.
i will go this way probably, BUT...

Before I completely discard the brick solution, I have one question that remains unanswered, maybe you can help. In an ideal word with infinite space available, with a 70cm internal dome, what would be the ideal dimension for the entrance width and length, and how big the hole that will connect to the chimney should be in width and length ?

I feel that if I have this dimensions I can sort out the problem. I am quite confident that I can create a solid tapered arc with 6cm x 11cm bricks, placed vertically and create a “hole” big enough to avoid the fire coming out from my entrance.

[david s]

For my design I had a similar problem in requiring the flue gallery to be really shallow in order to make it as compact as possible and fit on a 910 x 910 mm footprint. I have achieved this by placing it on top of the oven mouth rather than in front of it. Also by designing a generous volume above the oven mouth so smoke is drawn more efficiently by its inverted funnel form to the flue pipe. This however requires compound curves which are easy to do with a casting, but extremely difficult with brick units. To explain what I mean, take a look at the photo of one of my ovens that I deconstructed.
https://community.fornobravo.com/for...422#post398422

[Lucag]

Maybe I can plan the first external arc in a way that starts on top of the internal arc. This will give me the necessary space I suppose

[Lucag]

That’s unfortunate, beehiver
1.5 bricks is not enough because will it cause structural problem or because compromise the oven functionality?

What would be a good size for the opening in the fue area for a 70cm oven? Maybe if I find this out I can come up with a solution.

Do you have any suggestion to make a 70 to 80 cm brick dome work with my dimensions (137 round base). I will consider casting the smoke chamber / fue but I would like the oven to be in bricks

[UtahBeehiver]

If you are going to do what is called a tapered inner arch (recommended due to it is better and a smoother dome tie-in) if requires more than a 1/2 brick than you have shown. There are dozens of examples of tapered inner arches on the forum