Beaglestorm's Oven Questions

[dmun]

Re: Beaglestorm's Oven Questions

We've never seen a complete dome failure. Someone made a big deal of a picture of a dome where a brick fell down. They've been making ovens in this shape for thousands of years. Cracks? yes. Collapse? Not so far. We're not Kool-aide drinkers here: If ovens were falling down, we would be talking about it.

The catenary - high dome - low dome question is just conversation. You can be completely sure that a pompeii oven built to the plans will be strong and cook well.

[biondoli]

Re: Beaglestorm's Oven Questions

beaglestorm I really like your idea of the mini-tapering, really smart, ...I am thinking to follow your idea, thanks Carlo

[Dino_Pizza]

Re: Beaglestorm's Oven Questions

dmun & George:
Thanks about the dome shape question. It put my mind to ease. I've got my WFO site in the back yard ready for forming footings and Beaglestorms drawings is great (thanks for posting it!) .

Beaglestorm: Will you be putting the 2" of insulating board directly on top of a 4" concrete slab since there is no need for a vermiculite/concrete mix insulating slab?

[beaglestorm]

Re: Beaglestorm's Oven Questions

Wrote this before lunch but did not finish it and now most of the questions have been answered but I will still post it.. and yes I will be putting the insulation board directly on the concrete no vermiculite. It's actually 4" (2 - 2" layers in different directions) of Insblock 19 insulation for the floor.

I have been wondering about that question as well. I don't know if there will ever be a consensus. I am not a structural engineer, so I am kinda shooting from the hip based on what I have learned reading here over the past few months. I am still hoping a PE lurks around here and can give a calculated opinion.

The shape actually is an ellipse, or so says my CAD program, but overlaying a circle arc in the same space yields just a slightly different profile. I have not been able to draw a catenary arch in my CAD. I actually have a chain hanging on my wall right now to visualize it. I plan to print out my drawing full size then hang it on the wall and see how it matches up with the chain. RTFlorida did his with the same angled soldier but they were shorter and sat on the floor. Maybe he will give his thoughts.

I personally don't think that it really matters that much, after having seen the domes built on this site. With the hundreds that have been built? with 2? mortar joints to tight hairline builds. Arches of all profiles (most not true catenary), barrel, dry stacked brick box ovens, even just concrete and chicken wire. I am wondering if the is really enough weight to cause a short term failure. The haphazard calculation I did showed something like 2-4 pounds per square inch on the underside of the brick dome perimeter. I remember someone commented that a bad built dome may only last 50 years instead of 200.

Having said all that, I still not sold on the thought of all the outward pressure with the tapered soldier course. So, I think I am going investigate using the same height but eliminate the soldier and distribute the angle into half bricks all the way down using the mini-taper I drew above. I will draw it up and post it this weekend. I still have 2-3 weeks before my foundation is ready for the dome. Good luck and please share what you decided to do.

-Michael

[gjbingham]

Re: Beaglestorm's Oven Questions

Cool! Innovation and revolution. Me likes! What's the worst that can happen?

[beaglestorm]

Re: Beaglestorm's Oven Questions

Finally got sometime this weekend to redo the drawing to include the mini-taper. I had said I would post it last week so I wanted to follow through in case anybody wanted to see what it looked like. It really shrinks those joints and makes an 18" dome seem easy.

I’m almost sold on the idea of putting the dome back on the floor. (Thanks Dmun) You can still replace 85% of the floor bricks and it just seems so much easier and stable if you’re using a tall soldier as the first course. I can also make the floor 43" instead of 42" using the same space as I would be eliminating the 1/4" expansion gap and a 1/4" of extra floor insulation I had put around the outside edge. I know that I am dreaming if I think it’s going to be easy and that I am going to hit the tolerances in my drawing, but it sure helps for planning and building confidence. I also calculated that the little ?” expansion gap all the way around would have left what seems like a huge 33” square inches of total open space directly between the oven heat and the floor insulation. With the dome on the floor, all heat has to flow through the bricks to eventually dissipate through the insulation. The envelope just seems better with the dome on the floor.


On more question I had, was about the oven door (Pic #3). Taking 60% - 63% of the height I came to the compromise of 11.25” for the door height on the 18” dome. The 60% has been used for flat and arched openings with success. But comparing the two, an arched 12” door seem like it would release less heat than an equivalent 11.25 rectangular door. Do you all think an arched entry will allow you to squeak out a little taller door (3/4”) with out a loss in performance?

-Michael

[gjbingham]

Re: Beaglestorm's Oven Questions

.666666666666666666667 is probably fine for a ratio of entryway to dome height. You could always make you dome an inch higher to reduce the ratio. A 42 inch oven with an 18 inch dome height seems really low to me anyway.

I didn't read back to determine again what your planning, but it sounds like a pizza machine. The closer you get to 63%, the better the oven will perform. I wouldn't sweat it too much if you're happy with your plans though. A little more wood is all it will cost you. You definitely will lose heat faster than a similar dome with a smaller arch - at least that's my guess.