Steel Dome Oven

[brokencookie]

Re: Steel Dome Oven

Your smoke will always go from hot to cold. The larger the difference in temperature the better the draw. Somebody posted a spreadsheet that calculates chimney draw on the forum that you can use to check this. So.. Once you insulate, your oven will run hotter, creating a larger difference between the oven chamber and the outside air. Additional chimney height can also help.

Bruce

[Wiley]

Re: Steel Dome Oven

Thanks everyone for your imput.

dmun: we added an extra short (36") piece later during the trial and did not detect any difference. We were still getting a slight amount of smoke out the front. Of course things had warmed up a bit so it wasn't a proper test although it was still only a small fire. I would like to have an igloo rather than a gable framed FWO and so keeping the chimney as short as practical is desireable, supporting 6 ft of chimney presents its own problems.

Thanks Bruce I looked into the flow rate calculator unfortunately there are so many variables such as chimney throat shape that for me experimenting seemed the easiest answer.

One thing that crossed my mind during our morning walk. (we do 2 1/2 miles every morning sun, rain, snow, whatever the weather). When I constructed the ring that holds the chimney in place on the top of the transition piece I deliberately left about a 3/16" supporting lip all around the inside. That 3/16" x 18 3/4+ inches circumference actually reduces my X-sectional flue area by about 3 1/2 square inches. The 6" chimney X-section is nominally 28.27 sq inches, that support is reducing that to less than 25 inches. I should reduce the support ring to three small protusions and so recover a majority the lost area. It's an easy enough thing to modify. If I get 3 sq inches back I'll be increasing my present flue X-section by about 12%.

Here's a photo of the lip. Thoughts? Anyone see something I'm missing?

Thanks everyone, Wiley

[Wiley]

Re: Steel Dome Oven

Well, I did the modification to remove the excess chimney pipe support and reassembled the unit. I also extended the chimney to 4ft. It rained last night and all this morning and so the ground was soaking.

I decided to build a second bigger fire, not a super raging fire as without the heat sink of the 3-4 inches of basalt concrete I could easily reach 1000+ F in a single spot and perhaps cause myself some unwanted problems. As it was with this little fire I got the top of the dome to 625F within about 15 minutes. The smoke problem seems to be resolved. Here's a photo taken with the fire going.

Wiley

[asudavew]

Re: Steel Dome Oven

I'm really enjoying this thread.
Great design.
I have to agree with George about the cladding.

thanks for posting

Dave

[granvillearden]

Re: Steel Dome Oven

Great Job. I am considering one like this myself.

[Wiley]

Re: Steel Dome Oven

Thank you for the kind words.

I finished the excavation for the foundation today and two pallets of Quikrete arrived this morning. More than I need but since I have a few other projects in the works I only have to pay for one delivery.

My plan is to run to the quarry tomorrow to pick up a ton (one cubic yard) of 1/4 minus crushed basalt for the cladding. This is a bit early in the process for having that onsite but my friend with the big truck that can haul my trailer is going off on vacation. And then to pour the foundation in the afternoon.

If all goes well I should be stacking block on Monday and perhaps infilling on the same day. Good weather has finally arrived... at least a few days of it. :-)

I've elected to go with a "H" shaped stand with wood storage on one side and a two drawer bread proofing box on the other. I'll take pictures and post as things progress.

Wiley

[Wiley]

Re: Steel Dome Oven

Well so much for clear and sunny... more like light drizzel and overcast. Overcast is fine as it makes pouring concrete much easier as one does not have to fight the sun drying it out.

Anyway, off to the quarry as planned and the drizzel stopped by the time we were back. Below is a photo of 1/4 minus crushed basalt. My plan is to mix this with Fondu cement and use the mix to clad the outside of the steel dome. It certainly is less expensive than bricks. My trailer holds one cubic yd and also that is the minimum purchase/charge; the weight was 2220 lbs at a cost of $13.84 tax included. And with a yard one could build several domes.
Of course, it's only a less expensive alternative than bricks if it works. I'm thinking a mix of 1 part cement to 4 part basalt by volume. Anybody have any thoughts?

So the drizzel had stopped by the time we returned from the quarry and about 12:30 we started the pour. "We" being my wife and myself. Two hours later we were finished with the actual pour and screed and I spent 15 minutes or so troweling the surface about 2 hours later and again about an hour after that. Surface isn't perfect but level and smooth enough. Again pictures taken from upstairs bedroom window of before and after.

So depending upon conditions (if it stays overcast then sooner) I expect to be stacking block on Monday :-)

Wiley

[thebadger]

Re: Steel Dome Oven

Wiley,

Looks great. Don't worry about it. Once the blocks are on you won't even notice...

I'm getting close on my oven and I'm seeing the "light" - in that I should just "worry" about things that will impact performance or be seen when the oven is finally done. For ex. I was worried that the outside of my dome brickwork was messy. I then was like "hey" no one is ever going to see it...

Keep up the great work. Looking forward to seeing your steel oven completed.

Thanks
Dick

[Wiley]

Re: Steel Dome Oven

Here's the latest progress: Today I stacked the stand. It took longer than I expected and alot more energy than I imagined. I will pour the infill on Thursday.

I have departed from the plans and built a "H" shaped stand with two storage areas. One will be used for wood and the other will accommodate my recently acquired proofing box for bread. See photos.

I also decided on trying something different in regards to the lintels over the entrances. Instead of angle iron and notching the blocks I am trying inverting bond beam blocks and running rebar across and down to the suppport slab. The opening isn't wide and I feel/think/hope this should work. Time will tell. Again see photo.

As always thoughts and suggestions welcomed.

Wiley

[Wiley]

Re: Steel Dome Oven

Update for those following my progress. Yesterday I unstacked and restacked the base gluing the cement blocks together and to the base as I went. Today I bent the rebar for block cells and for the supported slab (hearth slab) and poured the infill. I guess I'll have to wait a few days before I can start framing up for the support slab.

Although I'm one tired puppy, it's the having to wait for the concrete to cure that's a real drag.

Wiley

[thebadger]

Re: Steel Dome Oven

Wiley,

Looking good. One thing I did was to use concrete board in place of wood when pouring the hearth. I just left the concrete board in place. Has a nice clean look to it as well.

Can't wait to see your "metal" oven up and running.

Thanks
Dick

[Wiley]

Re: Steel Dome Oven

Dick,
I'm assuming you cut the concrete board slightly larger than the hole and laid it on top and supported the piece until the concrete sets. I like your idea alot and by luck have a couple of 3x5 ft sheets of hardibacker left from another job. The hardibacker I have is 1/2 inch thick and it probably wouldn't need that much more support and since my space is divided into two, it wouldn't be bridging more than 24 inches in the short span.

Thanks alot for the tip, you just saved me a bunch of time :-)

Wiley

[thebadger]

Re: Steel Dome Oven

Wiley,

I think you can cut it to fit or to overlap... I cut mine to fit and all seems well.

I was paranoid about a "blow out" so I did use a lot of extra support. I wasn't sure of the strength diff between plywood/backer so I wanted to be safe than sorry. I think I used about 18 bags of 80 lb. quikcrete. I figure I can burn any of the 2x4 I have leftover.

Dick

[Wiley]

Re: Steel Dome Oven

Just as a followup on Dick's idea on using Hardibacker in place of the plywood for supporting the hearth during the pouring of the concrete. Today I cut two sheets of Hardibacker to be 3/4 inch larger all around than the two openings I have. My openings measure 2 ft by 4 ft... 8 square ft.

I then make a simple stiff leg consisting of a 30 inch piece of 2x6 across the top and a cut to length piece of 3 x 4 dunnage supporting that and resting upon a short piece of 2 x 12. This was to support the center of the 2 x 4 sheet see photo if that's unclear.

I then wanted to get some idea of what sort of weight it could support. So I started stacking 8 x 8 x 16 concrete blocks on the top. I stopped at seventeen blocks. Not because it was indicating problems, I think I could have placed many more, but because my calculations for weight of the poured slab (area supported by the Hardibacker) indicate it should weigh about 400lbs and I had 510 lbs on it in this test. I calculated the weight of the slab from the data on the bags. They said that it took 5 bags to pour 9 square ft at 4" thickness. That's bigger than the 8 square ft but gives a saftey margin to account for water weight. 5 bags at 80 pounds equals 400 lbs.


I then unstacked and glued the Hardibacker down to the top of the block walls and stacked until the glue cures. Tomorrow is a day off and Thursday it should be tight and I can proceed with framing for the slab pour :-)

This is certainly easier than cutting going the plywood route and for anyone thinking of a "H" shaped stand this might be something they might consider. Hardibacker is not that much more expensive than a sheet of 3/4 plywood and one does not need the extra support nor go thru the hassle of removal. When all is done I will simply reach in with my chainsaw. One cut and the support will be removed in a moment.

Wiley

[Wiley]

Re: Steel Dome Oven

Continuing Update: I tied the rebar and made the form for the hearth pour today. My plan is to pour concrete to the level of the inside line and then lay in my internal form for the vermicrete. Then pour the internal form full with vermicrete.

Once the vermicrete is poured, the idea is to add an additional 1" strip of wood all around the top edge of that form and set in the piece of high tech insulating board. This I got as a gift and it is unfortunately not quite big enough to fill the 51 inch by 51 inch area of the vermicrete. The areas not filled by the insulating board will be filled with more vermicrete. I'm using the board because it came at the right price (free), is most likely a better insulator than the vermicrete, and will create a flat surface upon which to more easily lay my firebricks. The final thickness will be 4 1/2 inches of insulation.

Once the main hearth and vermicrete have had a day or so to set up, the internal form will be removed and an additional 1 inch strip will be added around the top of the outside form. Then concrete will be poured in the remaining space.

With any luck I should be enjoying homemade WFO pizza by the middle of July! With final completion by ????

Wiley