Pdx 42" update

[MarkJerling]

I think the plans from Mark are the most helpful, and also the picture on the subscription page for the step-by-step guide:

Thank you for your kind words. Only thing with mine I'd change is I'd make the flue gather a bit wider. I believe I constricted it a bit much.

[Macrinehart]

Alright! Thanks to feedback I've enhanced my template so that it includes a cross section of the opening. Armed with a piece of string pulled through the hole in my template and marked for the Interior radius, I drew two layouts for possible opening dimensions.

On the left I have a plan with a 7.5" high opening wall to the base of the arch. On the right is a plan with a 10" opening wall at the base of the arch. The key learning is that the higher sidewall for opening requires transposing bricks to be set deeper in the oven dome, also the front of the opening is correspondingly less deep overall. There are also some differences in how bricks need to be cut where the opening and oven dome intersect. In both cases, after account for an additional 4.5" of depth to the opening in front of the chimney landing, there is plenty of space for the oven landing.

For good measure expanded the opening width by 1.5 inches per side to account for UtahBeehiver's advice on the reveal. Also took UtahBeehiver's advice with peak of arch at 13.25". (Thankfully, I didn't pitch that extra foam core!)

So, question: is there a preferance regarding the hight of the opening walls to the base of the arch?

[Gulf]

I'm guessing? that you are going with a segmental (axe/axed) arch. For ease of design, I have found that using the ID radius of the oven to determine the height of the risers for a segmental arch is very convenient. That will allow all the needed measurements for your plans to be included on one foldable 1/2 template. However, I highly advise a hemispherical arch for larger ovens. A hemispherical arch is much easier to cut, build, and doesn't require near the massive amount of buttressing that is by a segmental arch.

[Gulf]

Also, after a further look at your pics, they appear to show the risers going up on a slant. For a segmental arch, they will go vertical up to the skew back for the voussoirs

[Macrinehart]

Well received advice Gulf. The risers should be vertical, maybe the perceived slant is an effect of the camera angle, or my mediocre crafting skills?

I am partial to the segmented arch but your post reminds me of stuff I learned about arches in high school drafting class. Having the flattened arch puts more lateral pressure on the risers. I do like the look though. Maybe I just reduce the riser height to 5" and go with a steeper arch? Or for the architectural ideal I could use horizontally cut blocks for the 2nd course to get risers to 3.25" high, and then do the hemispheric arch.

I'll give it some thought.

[UtahBeehiver]

The placement of the bottom of the arch (whether full hemi or axe) needs the intersect the ID of the dome in order for the dome bricks to mate correctly to the arch. This is especially true for tapered inner arch configuration. Attached in an example from Mr Chipsters build showing an axe arch tapered inner arch as well as how it aligns with the ID of the dome.

[Macrinehart]

The picture says 1000 words! I think this means I need to set back a little further. Right now the interior radius (IR) is roughly lined up with the interior opening arch, leaving no intersection between the dome bricks and the arch bricks.

I appreciate all the feedback! Saved me a lot of headaches already! I do have a suggestion - I think getting an orthogonal projection set of photos on the arch and dome intersection (top, back, side, front, 60-degree perspective) would help a lot in visualizing how this junction is built. I also notice that a lot of straight on photos of the opening are really hard to see due to shadows. If these views don't exist yet in the forum I'll be happy to contribute when I've made it to that phase in my project.

[JRPizza]

Here is a cad side view I use to show how the TDC brick needs to be located so it falls within the inner and outer diameter of the brick shell.

[Gulf]

That's correct JR for a hemispherical arch. I recently got some first hand experience for a segmental arch on the Simmental Farm 36" and 48" Rumford Style Fireplace build. For it (my first rodeo with a segmental arch) I set the placement of the internal arch by that rule. We decided to scribe and cut the internal arch before building the dome. I found out while scribing the arch that the arch was placed too far forward. For a segmental arch the risers need to be set back further into the dome than the TDC brick to determine the placement of the face of the internal arch. We had to move the face of the arch in by 2".

Later, I was wondering if that could have been predicted in the original template. I think now that it could. Since the ID and OD radius' are the same for horizontal and vertical of a hemispherical dome, I use them on the half template to represent both. I use color coded markers to represent the top down and the cross section views.

In the pic below, I show the original drawing with the edits in black that show why the arch was moved backward into the dome in the field. The adjustment in the field worked exactly as the edit shows. The arch needed moving inward by 2". The risers were 9" high. A line from the inside of the first riser drawn to the to top riser makes that work perfectly. (remember that the template represents top down and cross section). I think that it would work for any size oven it drawn correctly. This is for a 36" ID oven, that will change as the size of the oven changes

Macrinehart, I recommend that you pick up some foldable cardboard project board from the dollar store. Two sheets will be enough. You already have the yardstick. Do that, and I may be able to help you with the internal arch placement. Also, there are some more pics on the above linked thread of a dry stacked segmental arch that shows several views of the cut arch. There will be others added as the oven was built and as I get time to update. Again, I advise a hemispherical arch for larger ovens as you 42".

[Macrinehart]

Thank you Gulf. I should no doubt listen to your advice regarding the hemispheric arch. I just have that vision in my head of what my oven should look like. But I promise you this, I will draw up the hemispheric arch plan on craft board as you suggest and see how it looks.

[JRPizza]

I also am a big fan of the hemispherical arch. I found the simple geometry to be elegant and very simple to work with. If you decide to go that way there are many beautiful ovens on the forum you can get inspiration from. I can help with the tapering if you need it.

[UtahBeehiver]

Plus 2 with what jr and Gulf says. Hemi are self supporting and you do not have to worry about buttressing the vertical side walls (especially swallow axe arches)

[Macrinehart]

Ok gang - I have my craft board. In my theme of not following directions I continued with foam core simple because I like the durability, and it was actually about 40% lower cost relative to the foldable project boards. I'm going to draw the front view first to get elevation, then transition to side view to plot the intersection of the arch and dome. Just pencil for now, the tip line is open for suggestions!

[Macrinehart]

Ok - opening is 10" IR with one rank side wall. I drew the Side walls with 1/8" mortar on the IR and 2.5" wide brick on the outer radius. Basically alternated back and forth measuring brick and mortar from the floor toward the keystone. The final measure on the keystone is 2 1/4" exterior width. Interior opening height is 12.75".

Any issues? Thanks!

[JRPizza]

Looks pretty good. You might want to think about getting closer to the FB recommended open width of 20"for a 42" oven. Your 11 IR will give you 22" which is OK but the wider it is the more heat you will loose. If you go with a 10 radius standing on 2.5" bricks on the bottom you will get a door height pretty close to the 63% of dome height that has been recommended and a 20" opening. My opening (for a 39") is about 19.5 wide by 12.25 high and I can get pretty much any pot we own under the arch. We do have a giant stock pot with a protruding handle on the lid that I have to slide in uncovered then reach in and place the lid, but that is not used very often.