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  #11  
Old 01-10-2013, 04:57 AM
Serf
 
Join Date: Apr 2012
Location: NY
Posts: 20
Default Re: dome shape?

Sorry, yes I plan to pour over the foam sphere and just use the trapedome as an outer shell. they don't make a foam ball big enough for the outer shell.....The wood forms should let me vibrate the pour.
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  #12  
Old 01-10-2013, 06:52 AM
david s's Avatar
Il Pizzaiolo
 
Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,881
Default Re: dome shape?

If you plan on using a castable refractory you will need to vibrate it or you'll end up with voids. How thick do you plan on making the cast section and how thick will the bricks be? Resulting in what total thickness for the dome?
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  #13  
Old 01-10-2013, 09:51 AM
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Join Date: Dec 2012
Location: East of San Diego
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Default Re: dome shape?

Logman- I feel your pain about wood vs brick. I can make lumber do what I want it to, bricks not so much. So do what you feel confident doing and learn along the way. its only time and money, right? That being said I think this concept has merit.

The calculations for any size dome should not be terribly difficult. There must be some programmer/math wiz/ computer guy that could make it happen. But for us pencil and paper types it might go like this.

Each course defines two circles inner and outer. For example a 36" cooking surface has an interior diameter of 36" ,duh, and a circumference of 113" (remember pi x circumference) exterior diameter of approxamitly 41" circumference of 128" (let us just imagine that is accurate )
Now then, the difference between the two circles is 15". From there you can determine how much to remove from each brick. So if the bottom course is 28 bricks, 15" divided by 28 bricks = just over 1/2 inch from each brick. I suppose a person could take that from one side but probably better to take 1/4" from each side- tapering to zero on the exterior.
I know that doesn't create a dome, but a cylinder. And this is where my geometry 101 class falls short. The 'top' of each brick could be beveled at an angle that is determined by the domes circumference, I suppose that is 41" in this example. The two circles of each course are also becoming smaller by an amount determined by the size and orientation of the brick.
Okay maybe the calculations are terribly difficult. However once determined and your saw is setup you could cut all your bricks- or at least each course all at once. The result would be near perfect. The surfaces of each brick could be glued together with almost zero gap/mortar. Practically freestanding.

Now have a little grace as you destroy my theory.

Last edited by PsychDoc; 01-10-2013 at 10:43 AM.
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  #14  
Old 01-10-2013, 10:34 AM
Serf
 
Join Date: Apr 2012
Location: NY
Posts: 20
Default Re: dome shape?

My inner form is the stryofoam 1/2 sphere. I'll put the floor firebrick inside after the pour to lower the effective dome height by a couple inches. The outer wall for my pour is going to be 3/4 MDF board triangles made up to form a trapezoid dome. I'm shooting for a 3 inch gap between the forms which i'll fill with KS-4V and vibrate as i fill it. Planning for a one peice precast instead of laying up bricks, hoping it works as well as some of the other hand-built forms I've seen here.
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  #15  
Old 01-10-2013, 12:48 PM
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
Posts: 4,881
Default Re: dome shape?

You will need to coat the inside of those mdf forms with some release agent. I use a mix of 50/50 motor oil and kero. Add 2% by weight stainless steel needles to the castable for added strength (optional) and if you make up your own castable brew add some fine polypropylene fibres, if using a proprietary castable these should already be contained in the mix. They assist in the elimination of water when doing the curing fires.

Last edited by david s; 01-10-2013 at 06:28 PM. Reason: typo
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  #16  
Old 01-10-2013, 04:45 PM
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Join Date: Apr 2012
Location: NY
Posts: 20
Default Re: dome shape?

Thanks David,
I am considering the stainless needles, and I have seen cooking spray mentioned (Pam) as well for a release oil. Are you getting the warm weather as well? From what I saw on tv, you might not need a fire for a pizza right now.
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  #17  
Old 01-10-2013, 06:31 PM
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Join Date: Mar 2007
Location: Townsville, Nth Queensland,Australia
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Default Re: dome shape?

Very hot and humid here (we live in the tropics), but we have just returned from Perth in Western Australia where, while it was just as hot, it was quite a dry heat so much more bearable.
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  #18  
Old 01-17-2013, 11:27 PM
Master Builder
 
Join Date: Jan 2013
Location: Japan
Posts: 610
Default Re: dome shape?

Hello all--I am a newbie to this community.
Just came across this thread while researching how to build an oven. I just finished casting a two piece dome using the trapezium shape. Same as a lot of people--feel more comfortable working with wood than with mortar and bricks.
Made both inner and outer mold forms from 2x10 materials. Began by laying out a 16 sided base --750mm diameter, then used the rules from that calculator site for angles etc. Long story short...takes a lot of time to fit all the pieces (glueing and screwing them together) but it came out fine. Tried to maintain an 80mm dome thickness. Inner 1/2 dome is 750mm outer is 910mm.
After completing the mold shapes, sanded and urethane varnished the surfaces. Prior to pouring the castable used Crisco vegetable shortening to lube the forms. ACG company sells castable refractory in my area through a specialty masonry supplier--each dome 1/2 took 100kg . Made a third mold that is an extension of the door area and base for the chimney--another 50kg.

Did the pour yesterday--starting at around 1PM and finished about an hour later. Thinking about waiting until tomorrow to open the mold, worry that the pieces will still be brittle. A lot of the other threads say you have to do a couple of ovens before you get the one you like-- that is the reason for taking all the time making the molds...I think the size is right but all the rest is up in the air.

It is sure nice to see all the information posted on this site.. don't have to feel like a pioneer!
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  #19  
Old 01-18-2013, 08:49 PM
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Join Date: Dec 2012
Location: East of San Diego
Posts: 52
Default Re: dome shape?

Mikku,

First, welcome.
Second, PICTURES!
Third, if you start another thread you will get more interested feedback
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  #20  
Old 01-18-2013, 09:12 PM
Master Builder
 
Join Date: Jan 2013
Location: Japan
Posts: 610
Default Re: dome shape?

Hello PsychDoc,
Thanks, I need to figure out PICTURES
The new thread is coming--Just spent 1/2 hour typing a reply and lost it somewhere.
New thread will be "CASTABLE DOME IN TOCHIGI-JAPAN", coming soon!
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