Second course angle

[dmyeli]

Hello everyone,

I am ready to lay down the second course of bricks and need some advice. My oven will be a low dome style oven, and I have already put down the 1st course ( I believe these are referred to as soldiers ) . The soldiers are full brick standing 9 inches high and the internal diameter is 36 inches.

My question : Do I need to be very fussy with the angle of my first course on top of the soldiers? This will be a low dome, remember, so according to the diagram on page 9 of the Forno Bravo 2.0 version, I am to use bricks cut at bout 70 degrees. However, this diagram on page 9 is the only info I've come across regarding the angle of this course for this type of style. Does this sound about right?

Other info : The oven entrance is 10 inches high, plus the additional area of the arch on top of which peaks at an additional 2 inches.

[mrchipster]

Re: Second course angle

Before you start the dome you will need to butress the soldiers what will be holding them up?

In most of the soldier applications I have seen the soldiers have an angle cut into the top to receive the dome.

Your inner arch will also need buttressing.

[texman]

Re: Second course angle

DM

You definitely want to start the dome curve in this next course. Like Chip says, most builders cut the top of those soldiers, but not required.

Are you planning to use an IT or a template to keep the dome curve true? Since you are building a low dome, i would suggest a template. A piece of plywood (or other rigid material) with the outside edge cut the height of the soldier and the inside edge cut to the height of the center of the dome. The will guide you on the angle required for each course of brick. Look at Octoforno template in the pic.

Si
Texman

[deejayoh]

Re: Second course angle

With a 10" door - I am assuming you want your dome height to be about 16" to make the ratio right at 63%. Given that you already have your 9" soldiers in place, you are going to need to angle the first course at about 50 degrees in order to hit that height.

You can use my spreadsheet to calculate the angles (see link in my sig). Set the diameter at 36", first course at 9", and IT height at minus 10.5 inches in order to account for how flat your dome is going to be. The angle for each course is shown in column N.

FWIW, you will not be able to use an IT to build this dome. And as Chip points out, you are going to need a whole lot of buttressing. Too much outward pressure for this to stay up on it's own.

Personally, I would cut those soldiers down to 4.5", angle the tops as Chip suggests, and build a more typical dome. You won't need that much height at the edges of the dome.

[shuboyje]

Re: Second course angle

First you need to find the radius of your dome. Once you have that use it to find the center point which will be way bellow the oven floor. Then simply extend a line from the center point to the inside top edge of the soldier course. That line will run at the angle you are after. Cad you be easier, but you could lay this out on the ground the old fashion way in no time.

[deejayoh]

Re: Second course angle

First you need to find the radius of your dome. Once you have that use it to find the center point which will be way bellow the oven floor. Then simply extend a line from the center point to the inside top edge of the soldier course. That line will run at the angle you are after. Cad you be easier, but you could lay this out on the ground the old fashion way in no time.

Effective radius will be 26.5", because the walls are high and the dome is so flat. He won't be able to use a string unless he can get the center point under the floor

[Tscarborough]

Re: Second course angle

The low dome makes for a nice oven, it is just a little more complicated to build.

[deejayoh]

Re: Second course angle

Here's the radius issue, in a nutshell

[mrchipster]

Re: Second course angle

Here's the radius issue, in a nutshell
[ATTACH]38237[/ATTACH]

Nice way to boil it down to the basics.

[david s]

Re: Second course angle

You can make some plywood templates for support or fill with sand to required form.

[dmyeli]

Re: Second course angle

Thanks everyone for all the information. I really appreciate it, and appreciate that I am probably well in over my head on this project - but I'll carry on!

Chip and Deejayoh - thanks so much for all your ideas - though I really don't understand the way dj boiled "it down to the basics" with the slick little diagram. Any further explanation on the "radius issue" would be wonderful.

Deejayoh - Thanks for putting the work into putting together that wonderful program. It will save me loads of time I'm sure. However, I don't understand some things....

For example, you suggested that I input minus 10.5 inches for the IT height. Can you please explain where you got this number from? My diameter is 36 inches and the distance from the radius to the top, inner edge of the soldier is 20.25 inches.

Buttressing - I have looked this term up and would love clarification on how it relates to building an oven. My assumption is that buttressing in this situation is a process by which an edge is cut into a brick and then the next chain / brick is set partially into this edge to promote some downward force as opposed to complete horizontal forces pushing outwards. I'd love it if anyone out there could clarify this definition for me.

How critical is it for me to buttress the soldiers? I have not seen anyone doing this - perhaps because most people are building higher domes.

Finally, my plan is to use sand to shape the dome. Any thoughts on this would be great.

Again, thanks everyone for taking the time to comment.

DM

[mrchipster]

Re: Second course angle

Because your walls (soldiers) are so tall and the forces related to the dome you are building are outward your soldiers will tend to crack apart. Or worse fall over.

Many builders have created cable or chain systems around the soldiers to hold them in. Others have built secondary walls around them.

With a hemispherical dome the force is translated into the floor in your case it is translated into rotational force into space on the tops of the soldiers.

[deejayoh]

Re: Second course angle

Chip and Deejayoh - thanks so much for all your ideas - though I really don't understand the way dj boiled "it down to the basics" with the slick little diagram. Any further explanation on the "radius issue" would be wonderful.

Deejayoh - Thanks for putting the work into putting together that wonderful program. It will save me loads of time I'm sure. However, I don't understand some things....

For example, you suggested that I input minus 10.5 inches for the IT height. Can you please explain where you got this number from? My diameter is 36 inches and the distance from the radius to the top, inner edge of the soldier is 20.25 inches.

DM

Hopefully I can break this down - What the graphic I posted showed is the shape of your current build - the diameter of the oven and the height of the walls - as the rectangle in the middle. The circle that goes around them represents the effective radius of the arc (circle section) that you will in order to connect the sides of your dome and still get the correct roof height (assuming I am right that you are targeting 16"). The thing you should take away from the picture is the rectangle + the arc at the top. That's the profile of the inside edge of your finished dome.

The reason that you need to input -10.5 in the spreadsheet is because that's the way the math works out for you to get a dome that is that flat. Don't worry about it, you aren't going to use an IT anyway. But if you decide to use a plywood form, you will want to base it on a 26.5" radius circle.

[texman]

Re: Second course angle

Buttressing - I have looked this term up and would love clarification on how it relates to building an oven. My assumption is that buttressing in this situation is a process by which an edge is cut into a brick and then the next chain / brick is set partially into this edge to promote some downward force as opposed to complete horizontal forces pushing outwards. I'd love it if anyone out there could clarify this definition for me.

How critical is it for me to buttress the soldiers? I have not seen anyone doing this - perhaps because most people are building higher domes.

Finally, my plan is to use sand to shape the dome. Any thoughts on this would be great.

Again, thanks everyone for taking the time to comment.

DM

I agree with Chip and DJ on the buttress. Those 9' soldiers and a low slope oven change the dynamics and stress of your build. It will work, it just needs some help around that first course to hold the dome as well as your arch. You may me able to incorporate the buttress into your outer wall. I will be honest though- I am not sure that you have much room to buttress that first course looking at the size of you stand. Hopefully someone has some ideas for you.

Texman

[shuboyje]

Re: Second course angle

Effective radius will be 26.5", because the walls are high and the dome is so flat. He won't be able to use a string unless he can get the center point under the floor

Agree, my typo from my phone probably made it hard to read, what I tried to say was you can do it in CAD or lay it out on the ground. Doing it on the oven proper won't work, darn pesky floor in the way, lol.