#11  
Old 09-10-2009, 07:55 PM
Lars's Avatar
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Default Re: How to draw/figure the door arch?

Hi Kim,
I just draw the arch using the bottom of the doorway as the center of a circle. Sometimes there's an issue with the sides ( will the arch, if too low, push the sides out) and then you might think about moving the center of the circle up to make the arch higher ( more downward force, less 'lateral' sideways force). Draw your bricks to scale, then just support a flexible piece of wood in there ( 1/8" masonite, or 1/4") and support it well with stacks of anything ( concrete block, bricks, wood frame)

There are MANY ways to implement an arch... and many pictures on this forum.

Good luck.

lars.
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  #12  
Old 09-10-2009, 08:45 PM
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Default Re: How to draw/figure the door arch?

Bear in mind as you read my response that I am, at the current time, a pure theoretician on ovens (I haven't started building my own yet). That said...

An arch/dome can be designed with various goals in mind. In short, there are multiple conflicting goals and restraints which must be satisfied on a per-design basis. Here's one possible breakdown:

GOAL: perfect structural stability
DESIGN: A tall catenary such that the forces at the floor are oriented almost vertically
PROBLEMS: not nearly the best shape for cooking (not bad for a kiln or an architectural dome however)

GOAL: cooking pizza
DESIGN: From what I've learned on FB, a low flattish dome is ideal, i.e., a relatively eccentric ellipse on soldiers, or even better, a low catenary on soliders (theoretically more stable than an ellipse)
PROBLEMS: Lateral forces on the soliders may require buttressing (apparently, the Pompeii has been designed to alleviate this problem, nicely done), low domes have tighter tolerances on brick wedge-shape to achieve a proper load-bearing arch without bricks falling through (mortar "glue" support not with-standing)
NOTE: In 2D instead of 3D an incomplete arch on vertical soldiers is called a "segmental arch", especially when a catenary is used. This is by far the most common oven-door and oven-entry shape on FB. The same buttressing problems apply of course, especially with a heavy flue/chimney.

GOAL: cooking nonpizza
DESIGN: a higher curvier dome, but still segmental on soliders because a full catenary is way too high for cooking. Segmental arches/domes conforming to a catenary, atop soldiers, will still be the strongest shape, my understanding is that ellipses are always acceptable if the catenary representing the force distribution remains within the middle third of the bricks (this rule of thumb is true of any arch: keep the true catenary within the middle third of the actual arch bricks).
PROBLEMS: less ideal for pizza (theoretically, although I question my own ability to discern the difference), same old buttressing problems on soldiers.

GOAL: aesthetics
DESIGN: whatever the heck you please
PROBLEMS: structural instability, cooking inefficiency

An important final note is that all discussion of structural stability is with regard to mortarless arches in which all force distribution and load support derives solely from brick-to-brick interactions. Ideally, no mortar is required. In reality, it is obvious that mortar can be entrusted with a significant fraction of the dome's load since many FB ovens are built to fairly inexact standards and there are surprisingly few reports of major structural failures. Note that an oven built from truely rectangular bricks, thus with no wedging whatsoever, must rely very heavily on the glue of the mortar to hold the dome together. The bricks still provide vertical support from the apex curving down the sides (transfered from brick to brick through thick mortar wedges of course), but more seriously, mortar (and friction in general) is the *only* thing preventing rectangular bricks from sliding along their radial axis toward the interior of the oven and falling inside. Since many ovens are built with rectangular bricks (and the Pompeii was designed that way), it seems obvious to me that mortar can be trusted to make up for a significant degree of imprecision in brick shape.

Follow-up, clarification, and corrections are welcome!

Cheers!
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  #13  
Old 09-10-2009, 11:01 PM
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Default Re: How to draw/figure the door arch?

I bought a door from FB, then built my opening arch around the door. The opening is larger than the door, but the reveal is slightly smaller.
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  #14  
Old 09-10-2009, 11:14 PM
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Default Re: How to draw/figure the door arch?

Stephen,
I think I spent the night in a tent near San Luis Obispo on my bicycle trip so many years ago down the coast of California ( SF to LA)

Kebwi: You need to start building. So many things become clear in the reality of bricks and mortar, and many other ideas and concepts get squished to infinitesimal size. There is much to learn from the process and it is, as you can tell, a lot of fun. I know in my case, things got much clearer as I encountered the process in reality. It starts with a slab of concrete. After 18 bags of 80lb concrete, things get a lot simpler. ( I should have said..."It is my lowly opinion that it would help you to begin construction"...sorry about that)
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Last edited by Lars; 09-10-2009 at 11:15 PM. Reason: apologize...
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  #15  
Old 09-11-2009, 06:32 AM
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Default Re: How to draw/figure the door arch?

@Lars: I'm going as fast as I can. :-) I'm on vacation this week so I'm not at home; I can't *do* anything except continue to research. My research is virtually complete however. I have a very clear picture of my goals and designs (which I will post once I get home). I hope to start digging up the yard this Sunday, fingers crossed.
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  #16  
Old 09-11-2009, 09:55 AM
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Default Re: How to draw/figure the door arch?

Here is how I waded through the tradeoffs.

First, I set my goals for the project.
1. Fun - certain amount of creativity, engineering, design and doing things I have not done before.
2. Pizza/baking - Pizza was number 1 - but cooking baking roasting - esp Turkey at Thanksgiving was number 2.
3. Being happy enough with the end result that I can entertain without feeling ashamed of my handiwork. - I'm a self admitted odd bird. I expect my first shot at anything I do to work and look good. Lots of pressure there.

So with that in mind I put pen to paper and started from the end and worked backwards with the design.

Lars said it better than I, but here goes.

I started to work forward with my over planned design and my plans and the exterior design changed/evolved as I went along. it happened as early as the block for the base. Stacking the blocks vs drawing the blocks made for improvements on ideas. All though the build, some aspects were kept, others were abandoned. And lastly - though I feel sheepish for saying it. Beware of feature creep!!! It could keep you building forever. I'm thinking of naming my oven Remington (after the house).

Christo
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  #17  
Old 09-11-2009, 11:06 AM
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Default Re: How to draw/figure the door arch?

[QUOTEIs it just me, or is the recent new wave of builders a little too focused on the math and creating the "perfect" (based on their intense calculations) geometric shapes?
Just my observation.
RT][/QUOTE]

I'm glad to "hear" someone say that cuz I was getting really nervous about this project!

Cecelia
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Old 09-11-2009, 11:48 AM
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Default Re: How to draw/figure the door arch?

Christo,
I am often surprised by the cool people like yourself on this forum. I had a look at your work after reading your comments, and, I have to say, 'wow... nice area'.


Cecelia,
Just look over the progress and philosophy of Frances....you'll be building in no time. The hardest part is where to position the doorway in the dome, and the transition from dome to entry. I am a firm believer in mathematical solutions, but I have built many things that introduce problems that you just cannot intellectually anticipate. Most mistakes can be overcome. There are two diametrically opposed schools of thought on the matter, and BOTH ARE TRUE!!!

Fail to plan, and you plan to fail...
Think long, think wrong!

Lars.
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  #19  
Old 09-11-2009, 12:50 PM
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Default Re: How to draw/figure the door arch?

Ah Thanks Lars!
I might as well update you on my build. I am a bit frustrated - but not yet in as bad as a mood as I deserve to be in!
I don't know if you all remember my earlier posts about the insulated hearth/extra thermal mass situation where we ended up having to take out the entire extra thermal mass, and re pour the insulated hearth? Which I did. Nice and thick.
Now I've been waiting to get going on the floor for a few weeks - or more. I finally got the lime, fireclay, sand and I have the portland cement ...and water. heh heh.
Anyway, my mental hurdles were the door opening (probably still is) and the transition to the door -
I had my son (the 17year old who knows all - I'm sure you all are familiar with the type) draw out a template - supposedly he wants to go into drafting and is taking his third year of it in highschool)- so he draws makes the template with the opening.
I spend half of Wednesday and half of Thursday laying the floor - I'm glad to. It's a nice change from being in the house in front of the computer and sink! BUT in order for me to take time out to go out there, I have to make sure I have back up in here - due to a one year old, and a bunch of others aged 5 and up.
Oh yes - I bought the brick cutter/tile saw from Harbor Freight - a "MAN" tool! Very exciting for the 17 year old, who, I might add, just purchased his own Milwaukee cordless drill that is way better than our old Milkwaukee - oh - get it!!! Old milwakee?!?! (I think I'm spelling it wrong...) and we are teasing him about his purchase and how now he must be a REAL man - His oldest sister even made him a badge declaring it!
SO, he tries it out on a few bricks - nice! Very nice! We both are very excited about it!
We think about putting the wall around the oven floor instead of on top - which would mean cutting bricks - oh boy! Yes!!!! But I, in my wisdom, had decided to just lay the dadgum floor and draw out the outlines for the dome and opening on the brick and build the rings on top of the floor.
Like I said, I spent those two days working on the floor, and was pretty much done.
Last night in a few short hours when my hubby and other children went to the 12 yr.old's football game, he took matters into his own hands. He drew the outline and was going to cut the bricks and lay the oven floor so we could put the wall around the oven instead of on top. He romoved most of what I had laid!
Luckily he hasn't actually cut into the bricks. BUT I now have another mess to clean up before I put the bricks back. Big deal, right? It's just time...and money!

Anyway, I planned on no Farmer's market this weekend in order to spend time bonding with my project. I did better without including my son! AAAACK!
And then to top it off, there is a new little family in town who seem to keep trying to pop in so we want to disappear and not be here to avoid saying anything embarrassing like, "go away" - or maybe something a bit nicer, like "oh, this is really a bad time for us right now...."
SO, do we go to another football game tonight or do I stay out there and work on the oven, and let them stand and watch me and get eaten up by mosquitoes?
heh heh heh.

Thanks for "listening" (I fear it might be too longwinded???)
Cecelia
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  #20  
Old 09-11-2009, 01:18 PM
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Default Re: How to draw/figure the door arch?

I have a suggestion for the new neighbors to be avoided: put them to work carrying 94 pound sacks of portland and they'll be gone in no time.
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