#21  
Old 07-06-2010, 09:52 PM
mklingles's Avatar
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Location: Portland, OR
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Default Re: Michael's 42" in Portland

Note: while my dome will follow a hemispherical shape, the floor is higher then the ecliptic plane of the hemisphere. The floor radius is 21" the dome height is 18".
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  #22  
Old 07-06-2010, 09:59 PM
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Location: Seattle, WA
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Default Re: Michael's 42" in Portland

Looking good Michael - nice work getting this far in just a few weeks.

One thing I've heard others say to watch out for is short bricks at the very front of the oven. Not sure how you are planning on finishing the front but having some small pieces up there can cause them to not be quite as stable. I'm sure it would be fine if you have a counter top or other material lining up with the top of the bricks to hold them in.

Have fun with the rest of the build - your getting to the good part and looks like you have a great start.
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  #23  
Old 07-07-2010, 05:41 AM
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Location: gloucester ma
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Default Re: Michael's 42" in Portland

Mklingles-Yes EXCEL is on the PCs-I am also building a 42 inch hemisphere Pompei because it has been suggested by the experienced builders that 1. it is easier to build; 2. the difference between the two is not great; and 3. now that I have the inner tunnel arches built (12 inches) I thought it was desirable to maintain the smallest door height to dome height ratio??? so all the heat doesn't go up the stack!

However I am concerned that my soldier course (which was laid as three chains on the flat to avoid the long vertical bonds) is seven inches high. The 21 inch radius of a 42 inch hemisphere will result in a 28 inch interior height. This makes the door height to vertical height ratio 12/28= .43


I see this is different than the often cited .63 recommended ratio, but somewhere in the FB site it describes that many Italian WFO have much higher domes. So I wonder if ..63 isn't the maximum recommended ratio?

Does anyone know how the lower door height to dome height ratio affects the air flow swirling in and out of the oven??

Last edited by Glosta; 07-07-2010 at 06:39 AM. Reason: typo
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  #24  
Old 07-07-2010, 07:33 AM
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Location: Los Angeles
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Default Re: Michael's 42" in Portland

Quote:
Originally Posted by Glosta View Post
However I am concerned that my soldier course (which was laid as three chains on the flat to avoid the long vertical bonds) is seven inches high. The 21 inch radius of a 42 inch hemisphere will result in a 28 inch interior height.
You can use a template cut out to your exact dome profile and adjust the I-tool to the template at the beginning of each new course level. This way you will not end up a slave to the I-tool and end up with a dome height completely out of whack.

George
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  #25  
Old 07-07-2010, 07:06 PM
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Default Re: Michael's 42" in Portland

@tfasz. I'm having a mantle stone cut to fit around the opening which will get mortared in place so everything should hold. IT's only 2in thick so I'll pour a layer of perl-crete to hold it up and surround all the rest of the oven floor.

@glosta: I'm no expert yet, but everything I've read hear and elsewhere says the 2/3 ratio of opening to dome height is very important. I emailed you a draft of the spreadsheet.

EDIT: NOTE - as pointed out by Neil2 below, both Alan Scott's bread builder's book and the Pompeii oven plans call for an optimal ratio of 0.63 percent.

Last edited by mklingles; 07-14-2010 at 11:25 AM.
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  #26  
Old 07-11-2010, 09:43 PM
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Default Re: Michael's 42" in Portland

To much life, not enough oven building. I did a bunch, but it always takes longer then I think it should.

Didn't get to start mortaring anything in place, but got the first two courses cut and ready, and the arch form and bricks are ready to go.





More photos here:
http://www.fornobravo.com/forum/members/mklingles-albums-michael-s-42-oven-build.html

Any thoughts on how long it will take me to get all that mortared together?
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  #27  
Old 07-12-2010, 11:22 AM
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Location: gloucester ma
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Default Re: Michael's 42" in Portland

Michael- that looks great--one thing you will run into once you begin mortaring is that despite valiant efforts to keep the mortar thickness as thin as possible; The mortar will spread the bricks apart farther than in the dry fit. Good luck glosta

Last edited by Glosta; 07-15-2010 at 08:20 AM. Reason: typo
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  #28  
Old 07-14-2010, 07:47 AM
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Thumbs up Re: Michael's 42" in Portland

Mike-regarding time to motar. It always takes twice as long as you think even when you have experience. An experienced mason would lay all four rings and clean up in a few hours. It takes me two to three hours per chain. My first three chains were vertical (ie no pitch). I got faster by the fourth row but was then slowed by the need to pitch chain 5 degrees. I pre-soaked all the bricks the night before to allow for a slower set and more workability time. Still the work time is only a few minutes once mortar applied to the brick. If you need to move a brick thats been down more than a few minutes, the movement will break the mortar bond; so its better to remove the brick, scrape off all the mortar from all surfaces, reapply mortar and reset it. After mortar sets 15 minutes I point up any gaps,,then 15-30 minutes later I gently wipe excess mortar with large tile sponge. On fourth row, I used the small wedges cut while angling the bricks to help support the 5 degree pitch. So even though I was getting faster-there was more to do so the ring again took about two hours to set plus cleanup.. Also given the additional mortar thickess over the dry set- you may find that you have to stop and recut a few bricks. Hope this helps. Glosta
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  #29  
Old 07-14-2010, 10:33 AM
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Default Re: Michael's 42" in Portland

"So I wonder if .63 isn't the maximum recommended ratio?"

This is considered the optimum for heat transfer from the fire to the brick. Too high a ratio (i.e. higher door) would result in the hot gasses escaping before they have given up their heat. Too low a ratio (i.e. lower door) will result in poorer and incomplete combustion.

This is not too say your oven will not work, just that you are likely to require a lot more wood to get it up to temperature.

Last edited by Neil2; 07-14-2010 at 10:35 AM.
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  #30  
Old 07-14-2010, 11:29 AM
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Default Re: Michael's 42" in Portland

@Neil2 - thanks for the correction. I did cheat my roof lower by 1" so my current plan is at 66% oven opening to dome height instead of 63%. I can either raise my roof by an inch (don't want to lower my door) or live with it. I'm skeptical that 3% variation will through everything off. I think I'll stick with my design choice, and if I have trouble getting oven up to temperature I'll build a "firing" door insert which will reduce the height of my opening to the optimum ratio.
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