Frank's Build

[fhausback]

The pyrometer is 8 channels and was new in the 50s (I think). I tested it last night with a k thermocouple and it’s fairly accurate. A modern digital version would be easier, but I like the look. Googling pictures of ovens, I came across someone that used the same model. I found this one on eBay.

[fhausback]

I'm trying to finalize my geometry, and am running into headscratchers caused by the size I'm going with. I like the idea of a 25" hemispherical dome, but does the 63% ratio hold true for this tall of an oven? 15.75" would be pretty tall.

I'm wondering if i'd be better off shortening the dome, to bring the door height down. I'd love to hear all your thoughts, and any comments on my sketch.

[UtahBeehiver]

Just making sure, we are talking a 50" ID oven. If so then 15.75" is right on. JR Pizza just recently post a historical study of WFO ovens in the Quebec area where researchers measure 30 plus hisotrical ovens and a majority of these ovens regardless of ID had arch openings the were in the 63% ratio, a few fell outside this tolerance. Look at his post then decide on what works for you, but once you lay the bricks it is a done deal.

[fhausback]

I read that paper, the chart that was included was pretty compelling. Unfortunately the authors did not include much detail on the height of the ovens studied.

My guess is that an oven designed to feed a Quebecois family for a week primarily on bread would be sizable.

[david s]

Just making sure, we are talking a 50" ID oven. If so then 15.75" is right on. JR Pizza just recently post a historical study of WFO ovens in the Quebec area where researchers measure 30 plus hisotrical ovens and a majority of these ovens regardless of ID had arch openings the were in the 63% ratio, a few fell outside this tolerance. Look at his post then decide on what works for you, but once you lay the bricks it is a done deal.

From memory that Quebec oven survey just took an average of oven opening sizes in comparison to their internal heights, but did not consider the performance of those ovens, so the survey does not equate the ratio to performance (correct me if I'm wrong). I modified one of my ovens to increase the entry height by raising the dome 2" without changing its diameter. So both the internal height and door height were raised by 2". This is a fairly drastic design change as the oven's diameter is only 21". I was unsure as to what to expect and was slightly surprised to find it fired cooked and retained heat no differently to an unaltered model.
James' sticky also subscribes to the theory that the 63% rule is nowhere near as important as many people believe. See here.
https://community.fornobravo.com/for...g-size#post764

[fhausback]

That's the problem with two different yet convincing arguments. If you don't match what others do, even small tweaks take a risk.

The average Quebec oven was around 63%, and ovens outside of a pretty narrow window required holes for additional intake or venting. Since all the Quebec ovens used an open front, with no integrated flue, i'm wondering if the current design everyone uses is more forgiving. I'd think you'd see a better draw thru a warm flue, compared to nothing or a large adjacent fireplace chimney.

That may also align with James' experience on ovens with flues.

[UtahBeehiver]

David brings up a good point, the ratio at least on the Blog is considered a "rule of thumb" these ovens are not exact science but rather a hybrid of science, craft and art.

[david s]

The pyrometer is 8 channels and was new in the 50s (I think). I tested it last night with a k thermocouple and it’s fairly accurate. A modern digital version would be easier, but I like the look. Googling pictures of ovens, I came across someone that used the same model. I found this one on eBay.

That's a ripper. I have two, not quite as old as yours, one of which I use on my kiln regularly. Unlike the digital ones they require no power and are far more reliable.

[GreenViews]

I'm trying to finalize my geometry, and am running into headscratchers caused by the size I'm going with. I like the idea of a 25" hemispherical dome, but does the 63% ratio hold true for this tall of an oven? 15.75" would be pretty tall.

I'm wondering if i'd be better off shortening the dome, to bring the door height down. I'd love to hear all your thoughts, and any comments on my sketch.

I just finished a low dome type oven and found it pretty easy to make. The hardest part was re-adjusting the IT every course for which I used a simple wood template. My radius was different than yours, but the lower dome concept the same. Some swear a lower dome provides better radiant heat for the top surface in cooking. Others say not that important. Personally, I have no idea being my first ever build. But the skill required was no greater than building a semi-circle in my opinion other than adjusting your IT. Just placed keystone 2 days ago. Check out my build page if you want to see what I did. I perhaps over-posted build pics and videos, lol. Others have said: "Whatever you build, you will love" Welcome to the oven building guild!

Tom

[fhausback]

Thanks for the feedback Tom. I'm a compromise between a super flat low dome and a spherical dome. This weekend i'm going to start laying things out to get a better feel for it, CAD sketches just aren't giving me a sense of scale. I did see your template technique and will be copying it to set my IT. I think it'd be a good idea to use even if i build a Spherical dome, just to keep an eye on the curve.

I did pull the concrete forms from the bottom of the hearth slab this morning. I'd be lying if I said i wasn't puckered up a bit pulling that wood out.

FYI for anyone building a form: I was planning on laying a sheet of visqueen over the OSB, and i forgot. Some of the moisture was pulled out of the concrete by the OSB, and the surface finish suffered a bit. The OSB seam that had ducktape over it to seal cracks has a perfectly smooth finish.

[fhausback]

Insulation picked up today from a local vendor: 4" of foam glass (what they could get quick), 2 layers of 2" calsil, and 4 layers of 1" aluminum silicate batt for the dome.

I'm not used to insulation being heavy...

[fhausback]

I wasn’t ready to start cutting insulation, so I worked on some accessories. I made a couple of steel frames to rest my firewood on under the oven, a simple andiron and a poker to move logs and cooking vessels.

The poker and andiron are welded up from SS square stock. I should have enough left to make a Tuscan grill. I held off on that because I don’t know if it’s better to have the grate steel flat, or rotate the bars 45 degrees so a corner faces up. I’ve seen both online. Any thoughts?

[BeanAnimal]

for anyone building a form: I was planning on laying a sheet of visqueen over the OSB, and i forgot. Some of the moisture was pulled out of the concrete by the OSB, and the surface finish suffered a bit. The OSB seam that had ducktape over it to seal cracks has a perfectly smooth finish.

vegatable oil, wd40, kerosene, or just about any other oil or petroleum product will help release the forms. I purchased actual form release, but I poured my stand walls and hearth slab. I spent $60 on 5 gallon pail, as it was all the local supply house had. I have 4.5 gallons left. I will put a gallo or two in a container and give away the rest. The bonus? It smells like cherry!

[fhausback]

I cut a 50” internal template for the base, and a 25” radius 1/2 circle for the dome and laid everything roughly out. The stacks of brick on the outside represent the outer surface of the igloo.

The horizontal 2x4 is the 15.75” top of the 63% opening.

I know it’s a big oven, but it now feels smaller than I expected. And the arch feels too high, i probably should flatten the dome a bit and bring down the inner arch height.

I also like the idea of making the outer arch a couple of inches shorter than the inner to help direct smoke up the flue, but don’t know if that’s necessary.

[UtahBeehiver]

I did put a lip on my outer arch to help direct the smoke towards the vent chamber. Only caution, you need to make sure you can get the door out that sits against the reveal of the inner arch. This means a larger reveal is needed on the inner arch.