Any flaws in my dome and arch design?

[stlouisz]

I am finalizing my design and would appreciate feedback on some of the features. It has taken sooooo long to get to this point.....

I am definitely building a 36" hemispherical dome, with a round arch, located in a house enclosure filled with insulation, and 3" insulation blanket. I'll be using a wooden arch template to locate the dome bricks.

I believe I have located the dome arch appropriately to intersect with the inside curvature of the dome.

I am trying to minimize the depth of the vent landing, for ease of use.

Does anyone see anything that might be a design flaw, I am particularly interested in thoughts on the following.

1) My design includes a heat break in the floor and between the dome and arch. Although I am a little leery about the structural effects of this, I believe it is similar to many successfully constructed ovens. In particular, I modeled much of it on Utahbeehivers' arch. The main difference is construction of the vent transition to the flue using insulating brick. This straddles the dome's arch and the vent arch, and would be a source of heat transfer.

My main intent is to maintain temp for baking on the following day. I will make an insulated door for the decorative arch as well. So, I'm not sure how much sense the heat breaks make in this situation.

2) Thoughts on depth of the counter in front of the oven?

Thanks,
Zoltan

[UtahBeehiver]

Re: Any flaws in my dome and arch design?

Hello Zoltan,

Nice CAD work. My drawings were done an old spiral note book (old school, I guess). Here are some suggestions:

1. On the "floor" heat break choose something other than silicon to fill the 1/2" gap. This is a high use area, use a piece of thin wall SS "u" or square tubing.
2. The inner arch seems to be inset a little too far in. The front side of the inner arch should protrude from the dome and back side should intersect the dome with a smoother angle.
3. Landing in front of oven looks good
4. Opening height is the right rule of thumb ratio, width looks good.
5. Insulating brick are a great product but they are not very strong. I would be a little concerned about how you fasten your chimney anchor plate to insulating brick.

Here is a link to a software program that will help you with developing dimensions for your arch bricks, inner, vent and decorative, if you so chose. Great start.


General Tools and Instruments

[deejayoh]

Re: Any flaws in my dome and arch design?

IFB are not strong, nor do they bond exceptionally well with mortar.

I don't think you get any benefit under the chimney either. Yes you lose heat of the chimney. That is what it's for! But only when the oven is firing. If you isolate the dome from the arch, that's about as good as you can do in terms of keeping the dome hot.

[stlouisz]

Re: Any flaws in my dome and arch design?

1. On the "floor" heat break choose something other than silicon to fill the 1/2" gap. This is a high use area, use a piece of thin wall SS "u" or square tubing.

I'm concerned about the conductive properties of metal. Alternatively, this might be a good place for thin strip of the insulating fire brick. If the exposed portions wears down, I can just allow ashes to fill the air space (which is what Kanoer54 did with a 1/4" air gap), or replace it if it gets really destroyed.

2. The inner arch seems to be inset a little too far in. The front side of the inner arch should protrude from the dome and back side should intersect the dome with a smoother angle.

I struggled quite a bit trying to visualize the issues regarding this. I thought I had it! I made a 3d model which shows that the arch projects out of the dome along its entire length. It projects 2" at the midline, which should be enough space to place the edge of my vent transition to chimney.

It also projects into the dome (most critically at its apex). I actually thought if the arch where only a little further away from the dome center, I would have issues with "drooping"? I made a close up view of the intersection of the dome and the top arch brick.

5. Insulating brick are a great product but they are not very strong. I would be a little concerned about how you fasten your chimney anchor plate to insulating brick.

You and deejayoh both bring up issues of its poor "structural" characteristics.
I don't want my flue being ripped off by a gust of wind. So I'll make the vent transition from regular firebrick.

Thanks

[UtahBeehiver]

Re: Any flaws in my dome and arch design?

ST,

That is why suggest thin wall U or tube, then you have an air gap. SS is not a conductive a carbon steel or aluminum. This subject gets brought up periodically. Do what works for you but this is a high usage are and you don't want IFB mixing in with your food.

[pluscwc]

Re: Any flaws in my dome and arch design?

Some things to consider:
1. I wonder about the stability of the arch if something happens to a mortar joint or brick at the top.

See merk's build and Gulf's questions about the arch

2. I've attached a pic of my heat break. It's 1" of 0.018" stainless wrapped over a piece of insulating blanket. You can't see in the pic, but the part that contacts the hot side is only a strip 1/4" wide the width of the opening. The cold side has legs for stability on each end, but most of the inside is cut away. The top 1" wide face will be covered with a door, so I just have to manage heat transfer there.

Just trying to illustrate one option for minimizing the contact of a stainless heat break.

3. In order to have an insulating door cover the entire hot surface of the dome, it will have to slide up into the vent. If you build a door that just fits in the entry arch, most of the dome arch bricks in the vent will be exposed still.

Congrats and good luck on getting started. I took years of (mostly) stop and go effort and am now a couple of weeks and one piece of chimney pipe away from my first fires.

[oasiscdm]

Re: Any flaws in my dome and arch design?

Hi

Excellent workups btw best I have seen.


This link takes you straight to the start of my heat break design. Check it out. It works very well. Remmber though when the fire is roaring the landing will get bloody hot anyway. I notice the difference once the oven is shut up tight . take door out oven floor really hot, stainless hot, landing warm.

http://www.fornobravo.com/forum/51/n...tml#post157620

http://www.fornobravo.com/forum/51/n...tml#post158361

[GianniFocaccia]

Re: Any flaws in my dome and arch design?

Zoltan,

As many times as I looked at your excellent oven drawings, I am still perplexed. Your profile view looks spot while in the plan view the oven arch (ala Russell) appears to be too close to oven center. (see pic #1 of my completed arch).

If you construct your vent attached to your oven you will lose a good portion of your heatbreak design. Your decision to use firebrick for the vent is a good one (IMHO), but you are now extending conduction area to the highly-exposed entryway area. My original design was exactly like yours, but I changed it per the attached photo. With my entryway completely separate from the oven, I am finding 3-4 days of usable heat following a pizza session. My record is 425F on the third day.

A slightly deeper outdoor entryway has benefits. The effects of wind on my fire initially blows smoke out the front of the oven, which I believe doesn't occur with short entryways found on indoor ovens. To keep your entryway shorter, you could build the oven arch so that it sits flush with the front of the oven.

Also, my floor gap is 1/4", which I believe performs the same as a 1/2" gap. You may want to rethink your floor heatbreak approach. Refractory caulk is highly toxic, while silicone will most likely break down.

John

[UtahBeehiver]

Re: Any flaws in my dome and arch design?

Zoltan,

I looked at the CAD drawing again and the first pic on post 4 shows your arch brick being 4.5 inches. If you are using a tapered inner arch, which I highly suggest. The arch bricks will need to be longer than 4.5" they could be as long as 7" (top dead center) of arch. Something to factor in. This allow a arch to protrude from the dome like GF and I were talking about.

[stlouisz]

Re: Any flaws in my dome and arch design?

Some things to consider:
1. I wonder about the stability of the arch if something happens to a mortar joint or brick at the top.

See merk's build and Gulf's questions about the arch

I saw that thread. I think the main problem pointed out is illustrated by my first attached image. The second image shows my original arch (better depicted in 3d), which has been built by others. The third image is a double arch for the vent. I am now considering this option and will post again with new drawings. Been working on the CAD all day it seems.

Some things to consider:

3. In order to have an insulating door cover the entire hot surface of the dome, it will have to slide up into the vent. If you build a door that just fits in the entry arch, most of the dome arch bricks in the vent will be exposed still.

Good point. I didn't show it in the drawings, but my thought is to have two doors, one for each arch and also something I could temporarily shove into the flue opening (6" diameter) when the fire is completely out.

Hi

This link takes you straight to the start of my heat break design. Check it out. It works very well.

Great pics....it will take me a long time to go through your build, since there are 98 pages!

As far as the heat break goes, I'll avoid the silicone and exposed IFB....maybe use minimal stainless on top of insulation or maybe cut the end of a firebrick, so it is very thin over insulation. Nonetheless, I'll probably just plan on a 1/4" to 1/2" space and address it later in the build.

[stlouisz]

Re: Any flaws in my dome and arch design?

Zoltan,

As many times as I looked at your excellent oven drawings, I am still perplexed. Your profile view looks spot while in the plan view the oven arch (ala Russell) appears to be too close to oven center. (see pic #1 of my completed arch).

I wonder if the arch looks too close to oven center primarily because my oven is 36" compared to many others which are 42". Also, the appearance of a thin 4.5" deep arch might contribute.

In the first attached image (plan view), I drew what I expect the first course of the dome arch would be in my oven. A significant portion is cut because of the curve of the dome....(hard to explain, please see pic). Basically, the brick would be only 2.7" deep here. Is this the problem that you and Russell allude to? Is this too thin?? At the top dead center, it would be just shy of 4.5". If I make the dome arch bricks 6.5" instead, then the thinnest part would be 4.7", similar to the rest of the dome.

Zoltan,

If you construct your vent attached to your oven you will lose a good portion of your heatbreak design. With my entryway completely separate from the oven, I am finding 3-4 days of usable heat following a pizza session. My record is 425F on the third day.

Wow! 3-4 days of usable heat....the lower mass of my 36" might not have that potential, but it's something to aim for.

Nonetheless, I agree and was aware of the downside of a firebrick transition connecting the dome and vent arch. I have redrawn my plans to include a double arch vent which now is completely separate from the dome. In order to do this, I increased the vent landing depth by 2.5". In order to minimize the change in view into the oven, I increased the opening ( and therefore the reveal to 1.5").

Option A is the original plan and Option B is the new....I am leaning towards B given my newfound knowledge.

Would 2" for the back arch be enough? I think I have seen arches that had similar dimensions.

[stlouisz]

Re: Any flaws in my dome and arch design?

Here are the CAD drawings of the 2 options... I tried to put the options side by side to aid in comparison...My brain now hurts....I need to go to bed.

[stlouisz]

Re: Any flaws in my dome and arch design?

Now I understand why my dome arch needs to be made from bricks longer than 4.5".

I moved the arch 1/4" further from the dome center and made them 1.5" longer.

I redrew the plan view and cross section for Option B. The plan view shows the first course of bricks, which makes it a cleaner drawing.

Since the depth of the vent and dome arch have increased since my first drawings, is the 10" depth of the counter still ok?

I was planning to cut a half brick while on it's edge (standing 4.5" upright) and fit it under a 10" Harbor Freight saw. Will it fit? Specs say it will only cut 3.5" deep, so I would have to flip the brick to cut through it.

[GianniFocaccia]

Re: Any flaws in my dome and arch design?

I wonder if the arch looks too close to oven center primarily because my oven is 36" compared to many others which are 42". Also, the appearance of a thin 4.5" deep arch might contribute.

I totally agree, as I didn't factor that in. (My oven is 39"). The other factor is how you build your arch. Some builders build a linear arch prior to constructing the dome. If you go course-by-course and sequentially cut your lower-tiered arch bricks in a circular fashion to match your TDC brick, your arch should end up circular in fashion in plan view.

In the first attached image (plan view), I drew what I expect the first course of the dome arch would be in my oven. A significant portion is cut because of the curve of the dome....(hard to explain, please see pic)

Agreed. (I think) See answer above.

Wow! 3-4 days of usable heat....the lower mass of my 36" might not have that potential, but it's something to aim for

I attribute my heat retention to insulation (5.5" under the floor and 4-7" around the dome). Keep in mind the 425F was achieved not opening the door once until the third day. If I cook something on the second day (lasagna, roast chicken, etc) the third day (225-250F) is usually only good for pulled pork or other slow-cooked braises, etc. Your oven should perform similarly.

In order to do this, I increased the vent landing depth by 2.5". In order to minimize the change in view into the oven, I increased the opening ( and therefore the reveal to 1.5").

You can achieve a huge benefit (IMHO) by simply flaring your entryway. With your understanding of the metrics involved in a build, I'm sure doing this would be a no-brainer for you. My reveal (1.25") is more than adequate to accommodate my door easily.

Would 2" for the back arch be enough? I think I have seen arches that had similar dimensions.

It should be ok, if your all-firebrick vent is integrated into your hemispherical entryway vault. I would be not so confident if it was a flatter arch with vertical entryway walls. I was tentative that my inner-entryway arch was only 3.5", but found that that my vent design helped solidify the entire structure. If I had it to do over again, I would have followed Colin's (oasisdm) rebated design, which allows for a 6" inner arch depth.

Nice job with your research and approach to your build. You should end up with a top-notch oven.

John

[GianniFocaccia]

Re: Any flaws in my dome and arch design?

Sorry, I just caught your last two posts, so here are my thoughts:

I moved the arch 1/4" further from the dome center and made them 1.5" longer

I used my wood template to tell me where to put my oven arch. I cut a second template vertically where the bottom of the arch would end up. See pics. I am wondering if this approach is viable with a 36" oven. I can only assume that if the door ratios are consistent with both sizes, it would work.

After looking at your revised designs, the amount of arch brick you have extending forward from the dome is not really needed. Why couldn't you swap 2" from the oven arch and 'give it' to the inner entryway arch?

Since the depth of the vent and dome arch have increased since my first drawings, is the 10" depth of the counter still ok?

This is totally up to you. Some ovens don't have any counter space in front of their oven.

I was planning to cut a half brick while on it's edge (standing 4.5" upright) and fit it under a 10" Harbor Freight saw. Will it fit? Specs say it will only cut 3.5" deep, so I would have to flip the brick to cut through it

Yes, you will have to flip your bricks over to complete cutting them. I started my build with a HF 10" saw, and finished with an MK101 contractor saw. With both saws, since virtually every one of my bricks was custom-cut, it was easier to rotate the brick against the stationary blade while holding it (firmly) in my hand. This also allowed me drag the face of each brick at an angle across the blade to end up with a concave curvature.

John