Nathan's 36" SoCal WFO build

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Closed the dome! If only the real oven went this fast!

[deejayoh]

Re: Nathan's 36" SoCal WFO build

Looks like you've done a good job of sizing the brick on each course so that you don't end up with the joints aligned.

Was there a formula behind that, or trial and error? Thinking I could update my spreadsheet to calculate brick sizes automatically

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

As long as the angle, looking down from the top, remains constant, your bricks will be staggered. If you're talking about the width of the brick, this will be a sinusoidal function. I can work out a formula but the way I modeled it, the model took care of the math for me.

[deejayoh]

Re: Nathan's 36" SoCal WFO build

yeah, I was referring to the width. I know if you just make them proportionately narrower, it works out - but looks like you went wider on some courses as you worked your way up. Don't spend any time on it, was just curious

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

yeah, I was referring to the width. I know if you just make them proportionately narrower, it works out - but looks like you went wider on some courses as you worked your way up. Don't spend any time on it, was just curious

They all get narrower as they go up, just not linearly. I believe it will be something like cos?* first brick width, where ? is the angle of inclination. 0? being the first course and 90? being the last. This of course will be a close approximation because of mortar joints, etc. I will check that and provide some drawings over the weekend if I have time.

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Now that the dome is done, I need to figure out the vent and chimney area before I start really laying some bricks.
I have .012" (.3mm) Inconel sheet available to me which would be, in my opinion, acceptable thermal transfer even though I was originally against metal. I think it's thin enough that it should be okay to cover an IFB or some calcium silicate. I also have access to the equipment required to make the design shown. The three options are:

Option 1: Use a 4.5" wide IFB (which is what is shown) and make an Inconel channel to go all around the top and bottom or the arch to protect the IFB.

Option 2: Use a smaller width, 2" maybe, of calcium silicate (similar to what is shown except thinner) and make the same Inconel channel to go all around the top and bottom to protect the calcium silicate.

Option 3: Place a 3.5" layer of aluminate cement and vermiculite to go all around the calcium silicate replacing the Inconel.

The Inconel is virtually free so don't consider cost. What would you go with?

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

I'm thinking about putting two sets of thermocouples in the oven. I'd like to put one set in the floor to measure top and bottom and achieve a differential temperature to figure out the saturation. I'd like to put the second set in the dome and also have one on the hot side and one on the cool side. From experience, what embed depth should the pairs be at? Also, what position in the floor and dome gives the best data?
Thanks

[GianniFocaccia]

Re: Nathan's 36" SoCal WFO build

I guess cutting all four sides is easy to say for someone who hadn't cut a single brick yet, lol. Now I'm torn. I really want to try it, especially because you say you haven't seen it... but I don't want to back myself into a corner either... decisions decisions

I tapered all four sides of the bricks in my dome, and to be honest, it doesn't take that long. It was fairly quick to draw two horizontal lines across the face of each brick and then trim the line off by rotating each hand-held brick against the running saw blade. Since I was trimming only 3/16" off the top and bottom of each brick, each cut added maybe 30-40 seconds per brick. It took much longer to bevel the sides of each brick than cut the tapers.

A more uniform mortar gap and a 'more engineered' oven is what prompted me to spend the extra time.

Cutting the top and bottom is a big waste of time and materials, imho

I agree - the process of cutting all four sides of each brick did take a little extra time, but no extra materials, really. I mixed up minimal amounts of mortar and since I got a pallet (377 bricks) of firebricks (irregulars that weren't perfectly rectangular) for $50, I didn't care.

John

[deejayoh]

Re: Nathan's 36" SoCal WFO build

I agree - the process of cutting all four sides of each brick did take a little extra time, but no extra materials, really. I mixed up minimal amounts of mortar and since I got a pallet (377 bricks) of firebricks (irregulars that weren't perfectly rectangular) for $50, I didn't care.

John

Don't you end up with a shorter brick face on the vertical? I haven't done the math, but seems to me if you trim 5 degrees off the top and bottom of each brick, you're using 10% more bricks to get the same face area. If bricks are free/fixed cost, I take your point. Most of us have to pay for each!

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

I see most people make the cal-sil board the same radius as the dome. Are there any reasons I shouldn't extend it out another 3" So that it will be about flush with the insulating blanket that goes around the dome as in the attached image?
Thanks

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

Got some time over Christmas to work on the design, so here is where I'm at.
There is 3 inches of cal-sil between the floor and the concrete entrance. It is capped with a .012" thk piece of Inconel. For the rest of the thermal break I plan to use vermicrete. It will be exposed inside the entry arch and vent area. Is this okay? The vent partially sits on the vermicrete.
Any other issues that anyone sees or anything else that I may have overlooked? I'm probably far enough along in the design to start forming for concrete unless someone spots an issue.

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

I have 3 options for the concrete hearth. I think option 1 is the strongest but most difficult, and three is the easiest and least strong. Do you think strength will be an issue with any of these options? If not, I think I'll make it easy and go with #3.
Option 1 - Single Pour
Option 2 - Pour a single flat hearth, then come back later and pour a second L shaped floor.
Option 3- Pour a single flat hearth up to the edge of the block stand, then later, pour another flat floor, partially on top of the existing floor.

For two and three I could drill into the hearth and insert rebar to anchor it to the entry floor.

[david s]

Re: Nathan's 36" SoCal WFO build

Any large cast concrete (either calcium silicate or calcium aluminate) section that is subjected to heat, particularly if that heat is uneven, is subject to thermal expansion stress. It is the primary reason most oven floors have unmortared bricks of relatively small units. The entry area is particularly vulnerable as the outside is in ambient air, also having cool air being sucked over its surface, while the part closer to the oven receives much more heat via radiation and conduction. If you have a thermal break then the conducted heat should be greatly reduced. My first oven (no thermal break) had a large fire brick (310 x230 x 80 mm) at the entry and developed a crack right down the centre. The brick was a heavy duty one rated at over 1400 C. I believe it was the uneven heat that it was subjected to that caused the crack. Not that cracking makes any difference to its function or performance.
PhotoPlog - Finished Ovens

[n8huntsman]

Re: Nathan's 36" SoCal WFO build

I see what you mean about a thermal gradient across the material inducing stresses but I'm a little confused about something still. I thought some people used vermicrete under their cooking floors as insulation? How would my vermicrete thermal break between the arch and dome be any different? Hot on one side, cool on the other.

[david s]

Re: Nathan's 36" SoCal WFO build

I see what you mean about a thermal gradient across the material inducing stresses but I'm a little confused about something still. I thought some people used vermicrete under their cooking floors as insulation? How would my vermicrete thermal break between the arch and dome be any different? Hot on one side, cool on the other.

The vermicrete, having lots of air in it is able to absorb minute cracks spreading. An example of this is IFB's being more resistant to cracking than dense firebricks, both bricks containing the same materials except the IFB's contain lots more air.