#11  
Old 09-30-2009, 02:51 PM
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Default Re: Full hemisphere arch?

Thanks as always. I'm certainly meticulous enough to cut and shape my bricks more than is required...but I was hoping to get away with no double-cuts, which means no wide-axis tapers. I like the trick of diminishing the brick width by an inch, which just brings it within the saw's reach. Doing so has another advantage too. It permits you cut the inner and outer arch bricks at the same angle since they correspond to the same radius of curvature. The alternative is to have the outer arch slightly larger to create a reveal, in which case the outer bricks must actually be tapered at a different angle than the inner bricks.

...my only concern is whether thinning the bricks to 3.5" weakens the arch. The thinner the arch-bricks are along the radial axis, the more precisely shaped and placed they must be in order to preserve a true self-supporting arch.

Cheers!
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  #12  
Old 09-30-2009, 03:17 PM
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Default Re: Full hemisphere arch?

I would highly recommend leaving a reveal for the door. You'll need it if you want to do any baking in the oven and it's obviously not something you can add later (not easily).

I think it would be fine to have both the inner and outer arches 3.5" bricks. They'll be much easier to cut, and I can't imagine that they would be less structurally sound (my exterior arch is 3.5" and very solid). Depending on the type of chimney you're building, you'll have to compensate for the slightly higher exterior arch, but you have plenty of options there.

I used the "Angleizer" software to calculate the tapers on all three of my arches. Worked great. Here's a screenshot of the calculation I used on my inner arch. My inner arch is 20" wide and rests on untapered half bricks to raise it to 12.5" (or maybe it was just 12", can't recall exactly off the top of my head). But in short, it's not difficult to change the jig to compensate for the different angle of your inner/outer arches.

The more time consuming part is creating good forms on which to build the arches. I was more meticulous with the form for my outer arch and it saved me time in the long run (see my pictures in the gallery section comparing the two). I reused the second form for my decorative arch.

Anyhow, if it would be helpful, I'd be happy to mail you my Angleizer CD now that I'm done with it. Or I can run the calculations for you.

S
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  #13  
Old 09-30-2009, 03:22 PM
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Default Re: Full hemisphere arch?

You could also cut (in two dimensions) every other brick, to make an arch with seven keystones, doubling up the keystone bricks:



This arch is drawn with a ten inch inside radius, and standard brick sizes.
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  #14  
Old 09-30-2009, 03:36 PM
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Default Re: Full hemisphere arch?

That certainly is cute dmun. It violates arch-theory in that not all of the bricks are wedge-shaped and those that are not can theoretically slide radially and fall out...but I admit that in practice these ovens seem to hold together regardless of theory. :-)
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  #15  
Old 09-30-2009, 06:37 PM
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Default Re: Full hemisphere arch?

Oh Dmun,
You may want to rethink that arch design. Arches are a continuous compression design. Think of squeezing the banana out of the peel. An arch like that relies only on friction and the sheer strength of the mortar to stay put. Masonry's strength is compression, its weakness is shear.

Keith - do you mean half circle arch? A full hemisphere is how the main body of most of the ovens are shaped. A full hemisphere is the rotated half-circle arch.

Just throwing in my two cents. That much closer to my forno bravo pizza cutter!

Lars.


WAIT--- I will leave my comment up there... but I may have been fooled by an optical illusion. DMUN, are those straight pieces? They look 'opposite wedge' shaped!
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Old 09-30-2009, 07:14 PM
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Default Re: Full hemisphere arch?

Quote:
WAIT--- I will leave my comment up there... but I may have been fooled by an optical illusion. DMUN, are those straight pieces? They look 'opposite wedge' shaped!
Yep, optical illusion: the straight ones are two and a quarter by four and a half inch rectangles.

BTW hundreds of pompeii ovens built with ordinary untapered bricks, held in with mortar, are withstanding repeated heat/cool cycles, hit with logs, tools, and unplanned calzones, generally under a lot of stress. If they are falling apart in numbers, we haven't heard about it, and I'm sure we would. You could build the arch with plain bricks only, and tapered mortar joints, and it would work just fine. My suggestion was just a little more refined visually than that.
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  #17  
Old 09-30-2009, 07:54 PM
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Default Re: Full hemisphere arch?

I had exactly the same thought Lars. I thought there were upside down wedges in dmun's drawing. Thankfully, I caught it before I hit the [post] button. :-) Nevertheless, my final response to his drawing stands...at least until I read his response above..........
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  #18  
Old 09-30-2009, 08:03 PM
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Default Re: Full hemisphere arch?

Lars, yes. I wrote hemisphere and meant semicircle. Didn't notice it until you mentioned it.

Thank you for the clarification.
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  #19  
Old 09-30-2009, 08:06 PM
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Default Re: Full hemisphere arch?

Yes dmun, thank you for the moment of sanity. I concede that these ovens stand up relatively easily despite possible architectural improprieties.

You have to understand, this is how I am. It has nothing to do with brick ovens. I'm a geek, I'm a computer scientist, I'm an obsessive compulsive pseudo mathematician (who isn't very good at math). Overthinking things is what I do best, and for someone like me, designing the oven is at least as much fun as building it...or dare I say using it.

Cheers!
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  #20  
Old 09-30-2009, 09:06 PM
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Default Re: Full hemisphere arch?

KW... I am glad you are aware of your condition. Was it Edison who or Einstein who said, 'definition of the problem is 95% of the solution'? I am completely familiar with 'overthinking' ( worked as computer programmer and SDM ...studied physics/engineering and LOVED the math.(BS, summa)) Even today I spent more time drawing a design for a firewood shelter than it took me to build the thing! ( not really , but close)

I stand by my post about the optical illusion arch. Sure many are made with straight bricks, but the most structurally sound have equally tapered bricks. A design that gives, even if it is only an illusion, the illusion of instability is unsettling aesthetically to me. That is only one small opinion.

I think this forum is quite amazing for the enthusiasm for design of domes and arches. The term 'architect' is misleading, since the advent of steel reinforced concrete, most architects act like 'ARTchitects'. There is really a thrill to designing a dome and arches, as we all have found out, or are finding out.

Just thinking out loud.

L.
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