Portable Oven Designs

[Xabia Jim]

I am giving a second oven a lot of thought....

How would you design a portable oven?

I want to build a 42" Pizza oven that's strong but lightweight (relatively) essentially using the Pompeii plans. Maybe we can do an lightweight version??

I want an oven that can be picked up with a forklift so I'm focused on the 48-inch reinforced hearth at this point (will consider a stand and/or trailer later). I can just slide the oven into the back of my pickup for now...pizza to go!

Here's what I'm thinking...please comment!

The first element to me is the most critical as it needs to be stiff. It will look a bit like a pallet as I want to pick it up with a forklift. In fact I'm going to disassemble a pallet to use those side wood pieces for a form with the two tunnels.

The first layer is going to be reinforced and round, just bigger than the oven dome. I'm wondering how to best strengthen it. Ideas? Is steel mesh different than rebar? What about a double layer of mesh in the middle of 3" of concrete, separated by an inch? Are there stronger mixes of concrete to consider? Any lightweight options? What about fibers of some sort?

The hearth will follow existing plans using 2" FB board and firebrick. I'm not thinking about cutting corners here, should I?

Now the dome, would you start the dome on the hearth or on the slab? I've seen discussion that on the slab is better but I thought the hearth ...is there much difference?

Build the dome out of 1/2 bricks, put on their side. With a good FB insulation blanket, I think that will work. But would a 1/3 brick be better/stronger? Not that big a weight differential.

A layer of FB mix over the dome, FB Blanket and Vermiculite concrete...

Sounds simple enough....

I'm most concerned about how to minimize cracking when moving.

For now it's the perfect virtural oven.... at least in my head!
If you were to do this, what would you be doing?

There are enough good minds here to get it right!
Jim

PS...Any estimates on weight?

[Xabia Jim]

Re: Portable Oven Designs

After posting this I saw a number of ovens along the side of the road today (as a garden center). from 90 cm to 140 cm (55 inch). They were on a three inch shick quare pad with lifting rings in each corner. They were a stucco over brick dome with a center chimney cheap split door ,and damper....don't know about the center chimney but they were the cheapest ovens I've seen...I'll get some pics.

[edschmidt]

Re: Portable Oven Designs

Are you talking about a mobile oven, or one which can be moved when necessary? I used to work designing mobile homes, and the funny fact is although they are mobile something like 95% never are relocated (unless you count the dump). So the question is if you are talking about designing an oven for an eventual move which may, or may not happen. Ill bet you would have more time in the initial design modifications, and the tear down and re-setup than you would building a new oven.

But if your talking about a mobile oven, THAT I can understand.

[Xabia Jim]

Re: Portable Oven Designs

In designing a mobile oven (one to be used on trailer or vehicle), it would also fit the bill for one that would be portable (that could be moved from one house to another). I am assuming that a lightweight but extrastrength oven could be both.

I imagine it would be quite difficult to leave your baby behind...

I have hauled my paella kit all over Michigan...birthdays in Ann Arbor and Grand Rapids, weddings on Lake Superior and Lake Michigan shorelines, company parties in Porter and Marne....maybe Pizza is in the future!

So I'm serious...what are my challenges? Weight? Cracking?

[Frances]

Re: Portable Oven Designs

You just want to build another oven... go on, admit it .

[Xabia Jim]

Re: Portable Oven Designs

Frances....I do like playing in the mud. The last one was a prefab and it kind of cheated me out of the pleasure masonry work brings....truth is it will help me with my disorder (WFO separation anxiety)

....gotta be some more comments out there??
....all I can say is bring 'em on....

[gjbingham]

Re: Portable Oven Designs

XJ,
The thought of picking it up with a forklift scares me. Have you ever seen big trucks on the freeway carrying long concrete girders intended for bridges (I assume). Those babies flex and sway as the trucks bump on down the highway.

Concrete is a very strong material but does have some flexure. I have no idea what the numbers are and whether there would actually be significant flexure between the relatively short span between the forks on a forklift. In my head, I can imagine mortar joints popping when you picked up the oven. Then again, it might pose no problem at all.

If I was going to build a mobile oven, it would be permanently attached to a dedicated trailer and leave it on there.

[Xabia Jim]

Re: Portable Oven Designs

Thanks George, that's the kind of discussion I'm open to.

With reinforcing, I don't think there's that much flex. I see a lot of ovens here that are being lifted by the 4 corners with a 3 inch slab. It's only 48 inches wide which is not too great a span, particularly with a few rebar cross members.

Reading about ferrocement boats and knowing what the waves on the oceans can do gives me some confidence. That's why I'm thinking about double wire mesh layers and whether to include fibers too!

I'm actually worried more about vibration moving down the road....maybe a rubber gasket layer between the oven and the truck.

Jim

[cvdukes]

Re: Portable Oven Designs

Jim,
For the rigidity of your "slab", you can't do much better than an absolute strenght to weight ratio of a ferro-concrete using a wire mesh in a box girder type design. See attached rough sketch.
This would be a shallow box made entirely of ferro-concrete. The sides of the box would extend below the box on three sides for rigidity. Fourth side would be open to slide the forklift in. Sides of the box extending above the slab would provide additional rigidity. The floor of the box needs only be 1 inch thick...1 layer of concrete reinforcing wire and 3 of favorite mesh (I'm partial to chicken wire...but then again I'm cheap). Sides and center beam would be the same... only 1 inch thick. Top to bottom height of the side walls of around 10 inches would be incredibly strong. If you want overkill, You might need to connect a couple of shallow ribs crosswise for side-to side flex.
Something like this would weigh 100- 120 lbs for the slab structure between the concrete and the mesh wire. Figure you'ld fill the box with a vermcrete or percrete... and then build a hearth floor etc. on top of that. (you also know I'm partial to a ferroconcrete dome, which would weigh a lot less than your brickworks...)

One other consideration: don't make the front to back depth of the slab longer than 1.333 times the lenght of your forklift blades. You don't want more weight sitting out beyond the blades because then it could tip off the forklift. Envious of anyone that has such easy access to a forlift!

[Wiley]

Re: Portable Oven Designs

"(you also know I'm partial to a ferroconcrete dome, which would weigh a lot less than your brickworks...)"

Could you expand on the "ferroconcrete dome" you are speaking of? I tried a search and this is the only thread the search returned. Thanks

I'm toying with the idea of a steel dome with 4-5 inches of refractory concrete with basalt as the aggregate over it. Topping that with 2 inches of vermiculite mix and then a 1" layer of frax. I have a 5/16ths inch thick 40" ID dome. Thoughts?

Wiley

[cvdukes]

Re: Portable Oven Designs

Threads I talked about various ferro-cement domes

http://www.fornobravo.com/forum/f3/f...oven-2938.html

http://www.fornobravo.com/forum/3212-michaelthebaker/

http://www.fornobravo.com/forum/f36/...ject-3464.html

[mine]

Re: Portable Oven Designs

I have a 44" dia. 1/4 thick sphere that I initialy was going to use as an oven until I happened upon this site.

The thought was to split it along it's equator, insulate the top and bottom with castable refractory, make a supported hearth with a gap around the circumference and heat from the bottom with wood/propane with the chimney protruding several inches below the center of the dome top.

I could not come up with a satisfactory way to line the inside, especially the top, and still allow the differential expansion of the refractory and the steel.

So I am making a "conventional" WFO.
Still open to the steel sphere if anyone has any good ideas.

[cvdukes]

Re: Portable Oven Designs

Wiley,

As I gather, you got a metal dome already that you intend to cover with concrete. Problem you may run into is the metal expansion coeffiecent is higher than the concrete. The size of the metal dome is big enough that its going push the concrete a lot...best case is that the the materials will just separate but worst case could be the concrete will crack. May not be a major problem since its going to be encased in other materials... Also, that sounds like a lot of thermal mass to heat for up those kinds of thicknessess....start your fire midweek for the weekend parties?

[Xabia Jim]

Re: Portable Oven Designs

I'm toying with the idea of a steel dome with 4-5 inches of refractory concrete with basalt as the aggregate over it. Topping that with 2 inches of vermiculite mix and then a 1" layer of frax. I have a 5/16ths inch thick 40" ID dome. Thoughts?

Wiley

Wiley: I had the same impression on thermal mass for your oven....lots.

If you read on thermal mass and insulation here (FB forum) you will find that many like a thinner dome with insulation...particularly for pizza

More thermal mass is okay, particularly for the bakers and commercial operations that will use the oven for longer periods.

Jim

[Xabia Jim]

Re: Portable Oven Designs

Craig,

any reason not to consider some rebar in the ferro mix (is there a negative, beyond weight)?

...and how do you avoid voids when laying it up? You're basically packing mortar into a mash of wires right?

and again, how thick were your dome and liner layers?

Thanks