3 centered segmented arch

[Jamie Dowdall]

Howdy everyone,

This forum is an amazing source of knowledge and I'd just like to thank the community who keeps it active and thriving.

I'm in southern ontario, Canada an hour north of Toronto and am in the initial planning phase of a WFO. I plan to get the foundation, stand and concrete deck poured this fall then acquire materials over the winter for my dome and enclosure. I really like dyerema's single pitched roof shed design with the timber post & beam style exterior framing and will be mimicking that.

One question I have is in regards to arch design. I'm a finish carpenter and have a lot of experience laying out different arch and ellipse designs and have always liked the look and function of a three centered segmented arch. Anyone ever built a dome this way? I think I've got a design for an IT that would work using a sweeping hinged design that will be able to adjust for different offsets from centered as well as different radius, but would like to hear from someone with first hand experience.

Keep the posts coming, I love reading all of your updates and tips.

Thanks

[UtahBeehiver]

Are you looking at doing a low dome oven or a pompeii oven. Low dome ovens sometimes have ellipitical shaped dome arches. If you are doing a pompeii (hemisphere) then you only need an IT that is fix pivot point at center of oven but adjustable in length. Let us know, there are a couple critical items when building the IT that need to be factored in. On the segmented arch, are you thinking a cast refractory?

[Jamie Dowdall]

Sorry, I should have been more clear. Yes, I'm looking to create a low dome elliptical brick oven. Super complicated I know, but it's the look I'm going for and the math/angles dont intimidate me. Using a 3 center arch I can create templates to find the pivot point of each course. The IT will have to be adjustable along the springing line and its length. Really want to take the time to get this figured out, but was just curious if it had been attempted by anyone here.

[UtahBeehiver]

I have seen offsetting IT before but somewhat rare and I can't recall if it was for an ellipitcal low dome. Download the eplans from FornoBravo, they are free and in the plans there is some general discussion on low vs hemi vs barrel shapes. But more important is the recommended ratio of the height of the oven opening. Typically low domes have a fairly short entry height vs the attached picture from the previous post (very high arch height). Nothing wrong with an low dome you just need to ensure the overall dimensions are proportional for oven type.

[Jamie Dowdall]

Thanks for the response Russell. I just printed off the forno bravo plans cause I'm sick of constantly scrolling back through on my phone while I madly scribble out sketches and ideas. I'm not a sketchup guy but I've got a very basic drafting background I'm trying to blow the dust off. May have to learn sketchup to get a 3d rendering of the dome arch transition. From what I'm seeing now it's going to be a real pain because it's going to be right in the heart of where the small radius transitions to the larger radius. I look forward to the challenge.

If I get anything on paper that resembles coherent thought, I'll post it for y'all to have a peek at. Harsh, honest opinions are welcome, dont want to overlook anything.

[UtahBeehiver]

I am a retired engineer but a pen and pencil guy as well. There are some on the forum that are Sketch-up or CAD nerd heads, that's okay too. What I can say, is keep in touch with up and go over your design on the forum before you do anything to crazy, much easier to correct on paper than once the mortar flows.

[JRPizza]

If you have a drafting background you might want to take a quick look at Freecad. I too had some training in the form of drafting in college and blueprint reading from my time at Boeing, and found Sketchup to be lacking for the type of layouts I wanted to do and Freecad did what I wanted. I had to read through a few tutorials first but there is great documentation on the web. It is easy for example to draw plan and side views and you can see them in iso if you want.

[Jamie Dowdall]

Thanks for the tip JR. Once I get some sections and birds eyes figured out in terms of dimensions I'll work on getting them plugged into the free cad software. Hoping I can use the software to find more accurate angles than a protractor on a scaled drawing. I have drawn the line at re learning the trigonometry haha.

[Jamie Dowdall]

Something like this.

[david s]

Sorry, I should have been more clear. Yes, I'm looking to create a low dome elliptical brick oven. Super complicated I know, but it's the look I'm going for and the math/angles dont intimidate me. Using a 3 center arch I can create templates to find the pivot point of each course. The IT will have to be adjustable along the springing line and its length. Really want to take the time to get this figured out, but was just curious if it had been attempted by anyone here.

There are a couple of other ways to do it rather than calculating all cuts or using an IT. You can cut a template from plywood to the cross sectional area. Another method is to build a sand castle to the required form and lay the bricks up to it, although it has the disadvantage of not being able to clean brick joints on the inside as you go.

[Jamie Dowdall]

I definitely want to clean from inside as I go, even though that tiny door will be hard to squeeze into near the end haha

[GreenViews]

Jamie, Very interesting. I was looking at at the 3 centered arch idea for my dome, but I wasn't sure my brick skills would match the elegance required. My build is kinda a mini pseudo version of that where I use a half soldier to go straight up and another half soldier to mostly correct back to my arch. This allowed me to have higher center of my main arch (less flat) which I felt more confident in being able to lay, but still gives me a little bit of 3 centered feel.

I hope you can do this well! I look forward to watching. Yesterday I mortared my first course and cut my second course except for my inner arch bricks. While I have the math skills for calculating the angles, one thing I've found is that my cheap 10" tile saw isn't quite up to the level of precision I would want. I calculated my side taper for the second course then found it difficult to figure out how to precisely cut that angle on the tile saw. Cutting bricks is definitely more complex than the tile cutting it was designed for. I'm also only cutting tapers about 2" back, or that's my plan at the moment as some people build with no tapers and others build with full tapers and some in between. With a lower dome, I certainly don't want to build with zero tapering. My first half soldier course I did zero tapering except for the top edge to match the angle required by the second course.

I am not sure at which course I will need to taper all edges to create a reasonably tight inner edge. I plan to take it one course at a time.... it is this lack of experience that caused me to go with a plywood template with radial lines pointing to my arch center rather than do the math ahead of time for the whole oven. I just don't know how to calculate actual width of each course. Something I haven't yet needed to worry about but is highly discussed is the upside down V. At later courses, may need to do 2 distinct tapers on the bottom edge of each brick? I kinda skimmed over this discussion so didn't catch the solution, but it is about the tighter circle radius affecting how the course below it meets the new course between two separate bricks. More power to ya! Cheering you on from Indiana!

Edit: I also used scale graph paper drawings, which I found quite helpful! I've learned from the forum that planning the inner door arch and dome intersection is of course critical. If like me you don't do a CAD rendering, perhaps make sure you do minimally a profile plan that includes the inner arch as well as a top down view and consider how each elevation of brick meets between your inner arch and dome. I was surprised how much my inner arch cut across a section of my oven, but each dome and door shape will have it's own profile of course. For me I ended up deciding on using 6" brick for my inner arch rather than 4" and moving into my oven a bit more (even though it really doesn't since I'm slicing off the front of the lower part of the arch and have the bricks longer so the back of my door doesn't take away from oven space) in order to make sure I had enough brick to meet my dome in a good way at the top.

[Jamie Dowdall]

I've got a lot of projects on the go currently but I plan to get my base and hearth poured this fall for a spring 2021 start. I'll have a 12" sliding compound with a masonry blade and a 10" tile saw with a blade that bevels. With these and a couple grinders with different wheels I feel confident in cutting any angles necessary. Going to tinker with different jigs before the build.