Dreamer turning to "do-er"

[MarkJerling]

Aha. Makes sense. Other than recommending a 6" slab or more think you have a good design.

[Blairt]

Pad is done. Ended up about 5.5" thick using 2x6 framing material.
I had leftover fiber-mesh reinforcing material from a concrete countertop project. This is about 1.5" below the concrete surface. In addition to the plentiful rebar, I think it should be quite solid! The weather here is dipping below freezing overnight so I had the tent/cover sealed off overnight with a heater inside. I've now got the heater in the storage area under the pad and the front entry closed off. Concrete is not getting to freezing temps.

Placed my order for firebrick etc today so hopefully will be able to start the fun part of the project in a few days!

[MarkJerling]

Looking good! Don't try to remove your supports under too soon.

[Blairt]

Frames are off. I've cut out a 51" circle to show where my oven will go (42" + 2 x 4.5" Soldiers). It doesn't look like it but the cardboard is centered on the slab. With 11" to the outer edge of the slab from the cardboard cutout, I have lots of room on the base for a 4" steel wall for my doghouse cover. I'll cut the inside corners off somewhat with cement board but most of the space will be filled with vermiculite over a 2" FB blanket.

My inner arch is 13" high and 20.25" wide at the base. I have my door arch frames cut so that the outer arch is 1.5" larger all around. Should make for a good seal around the door. My distance between the arches is 1.5 bricks or 6.75" If I go approximately 16" wide for the chimney opening before going into a square chimney above the arch, is this sufficient? I expect that I will go to an 8x8" square chimney once I am about 2-3 rows above the arch. (I need a full masonry chimney due to code here). Height will be at least 12' so there should be plenty of draw.

Is the placement of my inner arch correct in relation to the cardboard cutout and where my dome walls will be?

Next step is to cut the CaSi board to fit my carboard cut out. Bricks on target to arrive early in the week.

[UtahBeehiver]

The far right bottom of the inner arch needs to intersect the "ID" of the dome. Since the card board template is the OD and the ID is not shown, cannot tell if placement is correct or not. Also, are you really using soldiers and especially full soldiers, if so you need to be aware of the outward pressure of the dome and top of soldiers at the joint which may require some buttressing. Half soldiers or half headers would be better.

[Blairt]

Thanks - you're right. I only had the outer circumference shown. I've drawn in the inner circumference now - is this the correct placement for the arch?

I do intend to use half bricks for the soldier course - is there a preference to half headers over half soldiers?

[JRPizza]

Blairt a couple of things. You might want to consider making your arch forms narrower front to back, as arch bricks for most builds are shorter at the bottom (not full length) and longer at the top. having a shorter form with parallel arches front and back will give you the best chance of indexing the bricks at the proper location and angle. This worked for my arch and if you look at the first link below you can see how a deeper form would not have allowed me to use the rear part to locate my bricks.
Secondly, the arch needs to intersect the dome both at the bottom and the top, so at this point in the build some folks already have an IT built and are using it to make sure a brick sitting on top of the arch will mate properly. I verified mine both using a cad program (see capture in second link). I also included two pics to show the arch form locating shorter arch bricks and how I used my IT, arch form, and a couple of bricks to make sure the arch placement was correct.

https://community.fornobravo.com/for...899#post380899
https://community.fornobravo.com/for...319#post380319

[MarkJerling]

Thanks - you're right. I only had the outer circumference shown. I've drawn in the inner circumference now - is this the correct placement for the arch?

I do intend to use half bricks for the soldier course - is there a preference to half headers over half soldiers?

Your arch needs to be further "in" as the arc of the dome needs to intersect the top of your door arch.

[UtahBeehiver]

I disagree with Mark. The placement of the bottom inside is correct for a tapered inner arch. I do agree with JR that the form is too wide. For a tapered inner arch, a full length brick is used and cut back with the longest being the top dead center brick. See attached on how the IT is used to determine the various angles.

[JRPizza]

From my experience, the only important "datums" (control surfaces) on the arch form are the forward edge for indexing the arch bricks fore/aft (the rear edge is useless as brick length varies) and the front and back edges of the radius that sets the arch height and makes the bricks perpendicular to the vent arch. That said, the placement of the arch form should not be looked at relative to the inner rear edge.

I just figured out a way to use your cardboard template which I will try to explain when I get done with a few chores. It will help you locate your arch.

[JRPizza]

I have always recommended using CAD to help properly locate fore/aft placement of the inner arch, but if you are building a hemispherical dome oven with a hemispherical arch there is a simple way to determine location using any surface large enough to draw your dome inner and outer diameters in full scale. A large carpenter's square comes in very handy when using this method.

1. Using a marker with string, a large compass (bought mine at Harbor Freight) or your IT, draw two concentric circles representing inner and outer diameter of your brick dome.
2. Draw a line from the center of the circles out past the circle representing the outside diameter, which in my drawing is the lower horizontal line running to the left. This line represents the center of your vent/landing
3. Draw a line above and perpendicular to this line at a distance representing the height of your opening. This is a set dimension. In my drawing the line is at 12.25" representing the height for a 39" oven.
4. Now you can place a full size brick lying flat with the lower edge resting on this line, and move it fore/aft making sure it still lies in the area bounded by the dome ID and OD. If it does not properly intersect the dome you will have to go "out of round" to integrate the arch into the dome. The first and second picture show the extremes of fore aft placement. In the first picture the brick is in a more forward position, which provides for the largest interior cooking space, largest protrusion at the top of the arch to build your vent either on or over with a heat break, but also makes for a slightly longer vent landing. The second picture has the brick at a very rearward position. This can give the shortest landing, but cuts down some on the inner space in the oven and does not provide any protrusion for incorporation into the vent arches.
5. When you are happy with the fore/aft positioning of the brick, draw a line downward at 90 degrees to the horizontal line you measured your arch height from. Measure the distance from that line to the center of the oven, and you have the distance from the center to the front edge of your arch form. Build and shim your arch form so that the forward face is straight up and down (perpendicular to horizon) and if you index your arch bricks flush with the face the arch bricks will all be in the same plane and a door will have a good even surface to seal against.
6. With the distance from the center to the front of the arch set, you can now draw a similar perpendicular line at a distance equal to half the width of your door. I did this in the third figure at 9.75", representing half the width of my 19.5" opening. There are 2 bricks shown representing the most forward and most aft arch placements I looked at in the steps above. Lay the inner edge of a full size brick at the door width and position the forward edge at your arch forward distance. The the inner diameter circle now shows you the arc you need to cut on the bottom arch brick and will help you determine how deep you need to make the arch form. You can kind of see how wide to make the arch form. You should be able to index both the front and rear inner edges of the bottom brick (after trimming) against the arch form to keep the bricks in proper orientation fore aft and perpendicular to the centerline of the landing. This is what I was trying to show in the first picture of post #22 above.

[Blairt]

Hi all - thanks for the words of advice! JR - I wish I had access and knowledge of a CAD program but my degree is in finance not engineering . I can barely draw a stick figure...

So what everyone has said makes sense. I'm at a stage where I need to have actual bricks to play with and put into place on the arch to see where things should go. I had expected my materials to be delivered by the beginning of the week but the supplier didn't get them on a truck to the store until today. Now I'm hoping that they might arrive tomorrow so that I can work on things over the weekend.

I shortened the width of my forward arch template to 6". Hopefully that is near a sweet spot where it still has strength but won't get in the way of brick placement where the arch meets the dome. If it needs adjustment it won't take much to alter again...

[JRPizza]

I probably was not as clear as I thought I was being. You can take the cardboard template you have already drawn and proceed to step 2 of of my post. It would be really simple to find the proper arch placement without using cad - just something to measure with and something to draw an 90 degree angle. Either way good luck and keep posting any questions and progress!

[Blairt]

My bricks arrived!

In laying out the side arch bricks, I think I've finally got the placement correct - please advise...





Question - when you put the bricks in a herringbone pattern for the oven floor, how/where do you transition from that pattern in the archway tunnel where your heat break goes? Is it just a matter of cutting straight across the herringbone to insert your heat break?

[deejayoh]

That is too far back, and you need to make 2 cuts
1) to the edge of the brick that is inside the dome, cut it to align to the inner circle
2) to the edge of the brick that will meet the next brick in your first course - cut it to align with the angle of that brick