Steel Dome Oven

[randall4483]

Re: Steel Dome Oven Test Fire

I've taken several photos of the intermediate steps but figure unless the oven works they are not really that valuable. So today I assembled the pieces I have built on the driveway in front of my home and had a test fire.

So lots of things were "mock-up", the bricks on the hearth are old red bricks and in order to insure some sort of air-tightness I packed sand around the outside of the dome itself. The chimney was something I found at the recycle center (see where I shop :-)

I am including a photo of the three pieces before assembly. Also I would like to know (even though the photo doesn't show it) I did get a small wisp of smoke out the front, is that common or do I need to consider rebuilding my transition piece... in this case the hoop band that connects the chimney to he FWO? Thoughts and opinions welcomed.

Wiley

I thought in your earlier pics you had welded the rim onto the dome? Now it shows 3 pieces. Is the chimney piece made from a rim also or fabricated curve? What kind of work did you do before you retired? Very nice work.

[Wiley]

Re: Steel Dome Oven

John,
I don't feel limited at all by the capacity of my 40 inch. Although I am not skilled enough to bake more than one at a time at present there is definitely enough room to bake two or more at a time. I plan on getting into baking bread in my oven this spring/year (bummer, it snowed again this am :-( and planning on being able to bake 10 to 12 round loaves at a time in my oven. So a 40 inch closely fits my needs.

I have a friend with a WoodStone WFO that is 60 inches inside diameter and he rarely uses it as it take so much wood to get it up to temperature. So as one would expect there is no universal right sized oven it depends upon the need. What is your expected need?

50 cents a pound including cutting sounds like a reasonable price especially if you can be there when they cut the tank. It'd be great you can choose the half you want the ring on etc. They'll probably be cutting with propane not acetylene so if you can sweet talk the guy into cutting wide from the line you will end up with a nicer edge after grinding. If they cut with arc air you will definitely want a wide from the line cut. The old rule "cut wide and grind to the line" definitely applies if that's the case. I got a PM a day or so ago from a man with domes that are closer to your need but he's located in the east and shipping would be impractical and costly.

My top chain is 20 ft of 1/2" chain and only constraint is it needs to be able to pass thru the inside of 2" ABS DWV pipe.

Bests,
Wiley

[jcsforager]

Re: Steel Dome Oven

You are correct, I do not have interior dome yet.. But I have one picked out, Navy City metals in Bremerton has one that they are willing to cut and sell me 1/2 @ .50 per lb. Was going to get maybe next Wed? The big question as you mentioned is how much heat would I feel on outside w/ only 6"? I'm wanting as much room as I can get but laying out my pizza pan inside a 40" would still leave plenty of room. Do you feel limited at all with the space your 40" dome has? I talked w/ Ed last week and they don't have any tanks but he said keep checking. I've seen a few other tanks around, I may just slow down a bit and see if I can find a smaller dome. I got a bunch of chain but it has been chopped into many small sections...

thanks,
john

[Wiley]

Re: Steel Dome Oven

Fireart,
Thank you for the kind words. No, I'm not an engineer. What I did before I retired depends upon what time (year/month) of which one inquires. My father was a Professional Metalurgist and worked as a Materials Engineer most of his adult life and so I was exposed to that sort of stuff all my early life. He worked in the auto industry and then for Lockheed, I was also exposed to all that comes with such a life: layoffs, threats of layoffs, up and downs in the industry and such like. It wasn't what I wanted and so early on I opted for a different route for my life.

I've lived my life like a dog wandering down the road stopping to sniff any any bush that attracted my interest. Instead of living to work, I worked to live. And I liked to travel and experience different cultures.

I've always been a quick study and curious about how things work and how things were done. So lots of countries and lots of different jobs doing lots of different things. I've spent alot of time on and around the water and boats. It worked for me. I invested what money I made early on and let it grow. Married at 39 (to a wonderful woman with four daughters and far poorer than I) and retired at 49 1/2. I'll be 60 in a couple of weeks.

Years ago I happened to overhear a conversation at a party where my wife was asked what I did. I'm still pleased with her answer, "He does what is needed next."
Bests,
Wiley

[Wiley]

Re: Steel Dome Oven

John,
Please correct me if I have something wrong in what you said you have already gathered. You have a 60 inch sphere and at this point do not have an interior hemisphere. I would think in the best of possible worlds a 40 inch dome (like I have) would give you 10 inches of space between the two hemispheres for refractory and for insulation. Figuring 4 inches of refractory would leave six inches for insulation; and depending upon your pocket book you could go with 4 inches of ceramic insulation and two inches of vermicrete or three inches ceramic and three of vermicrete you would probably have more than safe temperatures on the outside of the sphere. Perhaps all vermicrete would work but I would try to go for as lean a mix as possible if I went that route. A fair bit of leeway there, I mean if you came up with a 38 inch dome that would be fine and a 42 inch would still be good.

I don't think I would be as enthusiastic about a 48 inch inside a 60 inch. My thinking is that I wouldn't want to go less than 4 inches of refractory heat sink and that would only leave 2 inches for ceramic blanket. And I would think you would be more "forced" into using the blanket. Probably still work but I suspect you would feel some heat on the outside shell after a while. How much heat is the question? So I would attempt to find a smaller interior dome and if you don't have any success (or they want too much) then go with a 48" if you have access to that.

So, if I understand correctly and you only have the one sphere/hemisphere at the moment I would suggest calling Pennisula Recycling at 360-379-9404 and asking what they have on hand in the way of half propane tanks. A man named Ed is the owner and his cell is (or used to be, people seem to swap providers alot) 301-1229 and I'm guessing that's still area code 360 as I don't have anything indicating otherwise in my roll-a-dex. Ed is willing to barter, dicker and horse trade whereas the ladies in the office think of the operation as more of a business...which I guess is what it is supposed to be. Another option is to call the various propane distributors and see what they have in the way of reject tanks (Suburban Propane in PT seems to always have a stack in the end of their yard). Depending upon your ability to "smooze" you might get a tank for little or nothing.

Good hunting and keep me posted. I have a 48 inch full sphere so if you have no success we could probably work some sort of trade. What was the length and size of chain came with the bouy? This year I am scheduled to swap out the top chain on my mooring. But like I said I would first try for a smaller dome.

Bests,
Wiley

[jcsforager]

Re: Steel Dome Oven

Wiley - This little forum is filled with goodies of knowledge! Been reading on the ceramic blankets. Looked it up on Ebay as suggested and found plenty.

Hoping to keep my weight down so I'm looking at this as an option. My previous post said my Buoy was 6'. It is 60" So I'm dealing with 6" of space, not 12" between inner dome and outer. Still should be enough for sufficient insulation. You used the Fondu as your refractory. Do you think a ceramic blanket would work on the dome?

I realize the importance of allowing room for the metal to expand and the blanket seems like it would allow this. Coat of foil/2-3" blanket/2-3" perlite mix? Looking for ways to stay light on my wheels... I'm also playing with idea that if I did cut dome from bottom ring up for the door to then have a few welded joints around outer edge of each dome connected to either metal framing or brackets extending to metal framing that will secure dome for road travel and preserve integrity of sphere..

john

[fireart]

Re: Steel Dome Oven

Wiley, what did you do before you retired? You must have been a Engineer of some sort but with hands on knowledge. Amazing work. Thanks for sharing.

[jcsforager]

Re: Steel Dome Oven

Good ideas.. I've been working with wood as my medium as of late and your comparison regarding tension holds true for wood as well. I built a Yurt once, using a tension ring around the top to hold the structure tight and when I looked closer at your design I saw that leaving the band does seem more intuitive/stronger. I may go this way. Good to think of though as I'm buying 1/2 of tank, not entire one so I need to get the 1/2 with ring. I like the idea of adding insulation and then refractory all inside the Buoy. The Buoy itself is really something I want as the oven "look". Getting it to my place was a whole adventure in itself. The guy told me it was 48 in so I brought a 6' trailer. Was loaded into the back of the trailer but stuck and I couldn't get it out. Ended up learning to use a boom truck and a day of screwing around but.. I have a really cool oven cap. I also got a bunch of chain and all the 6 braid rope that held the buoy. Will come in handy I'm sure in some way dressing out the trailer.. You were right on the propane tanks, those things are built like tanks and will make a pretty solid oven core. Still more gathering to do and few steps back for learning some welding but will be giving you some updates. Thanks for the ideas!
john

[Wiley]

Re: Steel Dome Oven

John,
You've been busy gathering materials... Great!

Wow, a six foot sphere, that's cool!

So if I am understanding correctly you will have a 72" +- hemisphere and a 48" hemisphere. That gives us a 12 inch space all around if one hemisphere was set over the other. My first thoughts are that I would use the 48" steel hemisphere covered with refractory like I did, something on the order of 4 inches thickness. Then fill the remaining 8 inches or so of space with insulating material (perlcrete or vermicrete). Built like that the roughness of the roadway or bumps would not result in a pile of dis-associated bricks. Also you would end up with a wonderfully smooth and weather resistant outer shell.

As for the question of cutting thru the backing ring or leaving it and cutting above (like I did): My reasoning (right or wrong) for leaving the ring was that these hemispheres are stamped out on a huge press and probably have residual stresses as a result. Heat that metal up and there is a chance it will move to release the stresses; cut the ring and any stresses may tend to flare the cut open and make the base out of round, even if it's cold and get worse when heated. Because the ring goes completely around it is acting in part like a tension member, sort of like the chain around a dome. Regardless, the inner voice was cautioning: "Don't!", so I didn't, whether my reasons were/are valid or not. I didn't want to burden myself with those possibilities, I wanted a circle for a bottom not something out of round, and unflat. And I feel such a fool when the inner voice says "Don't!" and I go ahead anyway, and it goes badly as a result. Embarrassed to myself, for myself, :-|

So I would still suggest leaving the ring if you can. It does make for a little bit more work in shaping the liner bricks, but bricks cut easily with a diamond blade. And I designed my oven so they all could be removed and replaced if ever they needed to be. The transition will fill with ash and if you wanted you could fill it with a mix of fireclay and brick dust and it would be near on invisible.

Also part of my decision to have the height inside decreased by the thickness of the bricks was the size of the split rim I had available for an entrance. I worked the math and decreasing the interior height made it so the radius of the rim was close on 63% of the lessened interior height. Close enough that the WFO draws fairly well.

I think your idea of simply pouring an insulating pad upon a steel deck is good. No need for the weight of a concrete support slab. 4 or 5 inches of vermicrete should more than enough protect the base. And placing the firebricks ontop of that would be the way to go. I would consider the idea of rabbeting out a notch in the sides of the bricks so that they could be set and locked together with a tennon either of slices of brick or high temp mortar. That way the interior hearth would act as a single unit. No bricks working their way up on a bumpy road. That may or may not be a problem once the bricks are locked together with ash and such.

I would suggest sketching it all out roughly on paper figuring what heights you want (interior and entrance) and where and what you can use to make the pieces from.

Looks like you are headed IMHO in a good direction.

Bests,
Wiley

[jcsforager]

Re: Steel Dome Oven

Hello Wiley,

Few questions as I plan this oven. I have obtained the Buoy. Bigger than I thought, about 6' diameter. Also should be obtaining 1/2 propane tank next week. Filled w/ water now getting the gas out. The tank is 48" diameter. So my #'s are for a large oven but bigger will be fine. I'm thinking of a thick layer of Perlite between two domes. Still working on ideas for connecting two domes and door but I'm first considering the pad these will rest on. Also, have been acquiring welding supplies. Have a neighbor who is will to teach me the basics. Bought an old and heavy Lincoln Arc wedler that will help w/ all this. I will need a troch though. Ahh, now I have a new project....

Because I'm doing a trailer I will have metal framing a few feet off the trailer deck. I'm thinking of pre-poured cement/refractory pad and set this first. Then Fire brick under inner dome only. I noted you cut your brick to shape of the dome thus decreasing inner ht of dome by 2.5". I also see the band of the tank continuous and the door cut out.

Do you think it would harm integrity of the dome to cut door out from edge up. I was thinking of cutting door this way, but now I'm thinking it may be best to insert bricks to allow dome to have continuos bottom rim. If it isn't that important I was thinking to frame up a square fire brick slab that would be just under inner dome. The inner dome would rest on top of bricks and would not decrease my 24" ht. Fire brick slab would continue out through door and make nice transition. The outer dome (buoy) is large enough that there would still be enough room of its inner ht to fit over inner dome and connect to slab. I could bracket all this to built up trailer frame.

Need to figure all this out before I cut door in propane tank.

john

[Les]

Re: Steel Dome Oven

Wiley,

It looks like Costco designed that for your oven - looks great! I see the challenge as sealing the two units together (water tight). There is a double sided tape they sell at automotive paint stores (it's used for attaching decals).

I wanted to build a pergola from the beginning but the wife objected - it would block her view of the yard. We were at a home show last weekend and she mentioned that we should build one - that's when the fight started.

Les...

[Wiley]

Finally some weather protection

So I've been on a search for something that would give some protection from the weather while using our WFO, especially our Pacific Northwest rains. I was in Costco the other day and spotted this outdoor cover, designed for covering a more typical BBQ. After talking it over with my wife, we decided that perhaps this would meet our needs. So we bought two, they are not inexpensive, costing more than I spent on the oven but upon assembly, they look like what we have been searching for. They are made of aluminum and it should be easy to cut a hole and build a weather tight transition for the chimney.

Here are some photos of one assembled. The number dots are still on the pieces and yes, it's sitting on some 2 x12s at this moment. The plans do not give any dimensions from which one could pour a concrete base without constructing the unit and taking measurements from it. At this point our plan is to pour two parallel concrete strips such that this unit could be supported where it is and the second supported approx 30 inches further away but inline to create an entrance between the two. My wife is a retired boat canvas worker (had her own business) figures she can create a cover between the two that would give good protection for that otherwise open area.
Here's some photos:

Wiley

[jwnorris]

Re: Steel Dome Oven

Oh, buoy...

I'm sorry, but I couldn't resist.

J W

[Wiley]

Re: Steel Dome Oven

John,

Looking at your picture what you have is a mooring bouy. Typically they are thinner than the propane tank that I used but in your case that is a benefit as you are thinking of using it as the outer shell. The bouys are typically constructed of segments welded together as opposed to two single sheet pressing halves welded together. It appears that the bouy you have is made of segments each of which is either a 1/4 sphere or 1/8th sphere.

Since this bouy has a weld around it equator cutting shouldn't be a problem. I would expect that they constructed this with a backing ring all the way around the equator weld. You will want to include this on the half you cut. I may not be clear on this but think of it this way: behind that weld (and running all the way around the inside of the tank) is a band of steel. That band maybe as much as 3/8" thick or as thin as 1/4 inch and maybe an inch and one half wide. When they constructed the dome halves they welded the top and bottom half of smaller pieces welded together on some sort of jig. They then welded the ring of which I'm referring to one half of the sphere. They the set the top half on top of the half with the ring. When welding the ring made for a sound weld as they could use more amperage and not risk burn thru and it kept the two halves in proper alignment (metal moves/expands as welded and alignment can be a pain if it is allowed for). This ring will aid you both in cutting the two in half as well as reinforce/strengthen the dome so when it is cut in half it will be less prone to going out of round. I expect the metal of the dome itself is less than 3/16 inch and maybe a thin as ten guage (1/8th inch). You will know when you go to pick it up as two men can fairly easily pick up a mooring bouy and two me would be hard pressed to pick up a propane tank.

I would suggest using the top half as internal corrosion will be worse on the bottom half. Also looking at the dents the top is less dented.

When you go to cut it I would suggest drilling a couple inch diameter hole about three inches down from that equator weld (on the bottom half of the dome. This will allow you to view the location of the internal ring of which I spoke. How you want to cut it is up to you, with the dome inverted I would mark all the way around the dome a line a small distance away from the backing ring. I would then run a grinder around the dome on that line to give clean metal to burn and to make a line not burned off by a torch. The actual cutting should only take a few minutes. Then grind to the edge of the backing ring.

As to your plan of one steel dome inside the other: I like that plan, it should result in something unaffected by any bumps in traveling. However, I would only have refractory material between the two shells (using a 48 inch with a 40 inch inside would give you about 4 inches of refractory) and have all my insulation exterior to the outer dome. The insulation is light and if you went with a doghouse type enclosure you could get away with filling the space between the domes and the structure with loose vermiculite or perlite. You might give Peninsula recycling a call, they are located just outside of Port Townsend and have contracts to cut decertified propane tanks. They sell halves like I used (mine came from them as part of a trade). Some people are terrified to cut decertified propane tanks (seen too many movies). Yes, they can pose a hazard but using common sense makes the cutting event free. Peninsula used to get tanks from as far away as California because the companies couldn't find anybody there who was willing to cut them!!! LOL What with the cost of fuel this past summer I bet they found somebody rather than pay for transporting them here.

It is unfortunate that you don't weld as there is a bit of fiddly stuff that takes some time...not a problem if one is doing it themselves but paying a professional welder might be a different story.

This answer is long and I apologise for that. There was some info the thread should benefit from as there might be others wanting to go with a steel dome. PM and we can go into details or you could come visit I live just up the road.

Wiley

[jcsforager]

Re: Steel Dome Oven

Hello Wiley,

Been enjoying your thread. Oven looks amazing. I have been playing with the idea of a steel oven for some time and was very excited to see your set up. My plan is to have a trailer oven that is built with as few pieces as possible so it doesn't shake apart on the road. My idea is based on a large steel buoy. I have a guy on Craigs List who has one for me, just need to pick it up. So this is where I'm at. I have read your ideas of two domes one inside the other. Great idea. For making pizza do you think it not enough for just one dome with cladding? The buoy is 48" so I could round up a propane tank that is a bit smaller and put this inside and have these two connected. I'm thinking a refractory sand may work as insulation between shells? I would love to chat with you more about this as you have some great ideas. My other issue is that I don't weld so I want to have all the pieces and draw up my plans to have this put together. From a welding standpoint I have attached a picture of the buoy. Is this a huge deal to have this cut in half? I was planning a fire brick floor and then welding brackets on the buoy to secure to the trailer....

thanks,
john