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  • #91
    In the FB plans, 6" ID is good for ovens up to and including 36".
    Russell
    Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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    • #92
      For small ovens like mine (21”) a 5” flue is sufficient up to 28”, then you should have a 6” flue up to 36” and 8” for anything bigger. The draw can also be increased by making the flue pipe or chimney taller. The inner diameter (or cross sectional equivalent if using a masonry chimney) is the more powerful factor than height for increasing draw. Also a smooth stainless pipe is better than a rough brick inner surface as it provides a smoother laminar flow.
      Kindled with zeal and fired with passion.

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      • #93
        Originally posted by david s View Post
        For small ovens like mine (21”) a 5” flue is sufficient up to 28”, then you should have a 6” flue up to 36” and 8” for anything bigger. The draw can also be increased by making the flue pipe or chimney taller. The inner diameter (or cross sectional equivalent if using a masonry chimney) is the more powerful factor than height for increasing draw. Also a smooth stainless pipe is better than a rough brick inner surface as it provides a smoother laminar flow.
        Got it. my vent flue is 12" deep i meed to get a 6 inch opening that makes my arch bricks if cut with even thickness it would be 3" each arch where the flue opening would be. Is this a problem? i plan on making the chamber tall so I can get a bigger pocket for the smoke and gases to accumulate as well
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        • #94
          Not really sure what you mean without an attached pic, but the principle is right a large volume chamber under the flue pipe prevents smoke exiting out the front of the oven, provided the flue size is adequate for the oven.
          Last edited by david s; 06-06-2019, 03:03 AM.
          Kindled with zeal and fired with passion.

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          • #95
            Originally posted by david s View Post
            Not really sure what you mean without an attached pic, but the principle is right a large volume chamber under the flue pipe prevents smoke exiting out the front of the oven.
            here is a rough sketch of the top view of what im talking about. does this help? I only have 12" so the opening would be 6" in the middle and 3" fire brick for th 2 arches or does it go by sq inches? can i have like 4 1/2" opening by like 8" wide which gives me 36 sq inches? then transition into the 6" or no matter what tje opening has to be at least 6"x6"
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            • #96
              Yes, it’s the cross sectional area that you work on. A 6” pipe has a cross sectional area of 28 sq in. The form of the flue gallery is difficult to build in brick without having lots of joints lining up. So much easier to cast where compound curves and a reduced mass are a breeze. A heavy brick flue gallery can act like a heat sink sucking stored heat from the dome.
              Last edited by david s; 06-05-2019, 04:47 PM.
              Kindled with zeal and fired with passion.

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              • #97
                Originally posted by david s View Post
                Yes, it’s the cross sectional area that you work on. A 6” pipe has a cross sectional area of 28 sq in. The form of the flue gallery is difficult to build in brick without having lots of joints lining up. So much easier to cast where compound curves and a reduced mass are a breeze. A heavy brick flue gallery can act like a heat sink sucking stored heat from the dome.
                David thanks for all the info...I dont know what i was thinking about the sketch I made my bricks are 2 1/2" not sure why I was thinking 3" I would have 7" between the arches.....ill have to read up on casting. so if I do cast would I cast in the stainless anchor plate for the flue? How would I transition from cast to the duravent flue pipe?
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                • #98
                  I made my vent 1.5 bricks deep and with that fed a 8" pipe. I extended my aft vent arch bricks over the inner arch by about an inch which let me make the arch wider along the top and use that inch to shorten the overall length of the vent. If I was ever to build another oven I might consider casting the vent, but that is an additional skill set and I do like the look of a brick vent.
                  https://community.fornobravo.com/for...372#post386372
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                  • #99
                    I cast my flue gallery and it is both shallow and very light because you can make a casting much thinner than the thickness of a brick. I have reinforced the sides with buttresses and the depth of the flue gallery is the same as the diameter of the pipe (5") This creates a very shallow entry which makes working the oven far easier. Nothing worse than having to work down a long tunnel before you get to the oven proper. This is probably too complex for a one off so another idea is to build the sides in brick and cast a piece for the top. If you cut away most of the square part of the anchor plate it can be placed on the casting when you get near the top so the base of the anchor plate is embedded in the casting. I don't use anchor plates, but fit the flue pipe as shown by making 3 tabs. Anchor plates are expensive and fitting by drilling into the brick is asking for cracks to be created there from the constant stress of expansion and contraction of the fixing. Also because the area gets pretty hot there, only stainless fixings should be used. Hope this is food for thought. There are many different ways it can be done, but brick units certainly don't lend themselves to complex forms whilst maintaining structural integrity.

                    Click image for larger version  Name:	P6160030.jpg Views:	5 Size:	523.6 KB ID:	413811Click image for larger version  Name:	P6160027.jpg Views:	4 Size:	410.7 KB ID:	413808Click image for larger version  Name:	P6060733.jpeg Views:	1 Size:	351.2 KB ID:	413805Click image for larger version  Name:	P2160559.jpg Views:	3 Size:	863.7 KB ID:	413806
                    Last edited by david s; 06-06-2019, 03:11 AM.
                    Kindled with zeal and fired with passion.

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                    • Originally posted by david s View Post
                      I cast my flue gallery and it is both shallow and very light because you can make a casting much thinner than the thickness of a brick. I have reinforced the sides with buttresses and the depth of the flue gallery is the same as the diameter of the pipe (5") This creates a very shallow entry which makes working the oven far easier. Nothing worse than having to work down a long tunnel before you get to the oven proper. This is probably too complex for a one off so another idea is to build the sides in brick and cast a piece for the top. If you cut away most of the square part of the anchor plate it can be placed on the casting when you get near the top so the base of the anchor plate is embedded in the casting. I don't use anchor plates, but fit the flue pipe as shown by making 3 tabs. Anchor plates are expensive and fitting by drilling into the brick is asking for cracks to be created there from the constant stress of expansion and contraction of the fixing. Also because the area gets pretty hot there, only stainless fixings should be used. Hope this is food for thought. There are many different ways it can be done, but brick units certainly don't lend themselves to complex forms whilst maintaining structural integrity.

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                      Im listening for sure and very interested in making this easier and efficient. what would be the casting recipe for this and thickness of the cast? . If i do the 3 tab method how does it stay secure? Do youu pack homebrew around it then?. and if i go with the anchorplate i would just cut away most of the square and place it in the wet casting leaving just the top exposed for the flue connection?. supervent sells stainless anchorplates for $22 not terrible price here.
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                      • I have decided to do the arch amd side walls in firebrick and then I will do a castable imverted fummel leadi g up to my 6" flue...i just have to figure out if I should make my own refractory cement or buy a bag already mixed
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                        • Originally posted by Chach View Post

                          Im listening for sure and very interested in making this easier and efficient. what would be the casting recipe for this and thickness of the cast? . If i do the 3 tab method how does it stay secure? Do youu pack homebrew around it then?. and if i go with the anchorplate i would just cut away most of the square and place it in the wet casting leaving just the top exposed for the flue connection?. supervent sells stainless anchorplates for $22 not terrible price here.
                          I do mine in a slightly more complex way to both support the flue pipe some 8" higher up and also to allow moisture to escape from the insulation layers between the two terracotta caps.High temp silicon to seal the top cap against the pipe. I use a proprietary castable refractory for the flue gallery (one inch thick) , but if you are doing a one off the home-brew should work fine as the top of the flue gallery does not see the same kind of temperatures as the inside of the dome.

                          Click image for larger version  Name:	P6070734.jpeg Views:	2 Size:	375.2 KB ID:	413824
                          Kindled with zeal and fired with passion.

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                          • Originally posted by david s View Post

                            I do mine in a slightly more complex way to both support the flue pipe some 8" higher up and also to allow moisture to escape from the insulation layers between the two terracotta caps.High temp silicon to seal the top cap against the pipe. I use a proprietary castable refractory for the flue gallery (one inch thick) , but if you are doing a one off the home-brew should work fine as the top of the flue gallery does not see the same kind of temperatures as the inside of the dome.

                            {"alt":"Click image for larger version Name:\tP6070734.jpeg Views:\t2 Size:\t375.2 KB ID:\t413824","data-align":"none","data-attachmentid":"413824","data-size":"small"}
                            is the home brew the same as the homebrew mortar recipe? i thought i seen gastagg used th 3 1 1 1 formula
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                            • Yes, 3:1:1:1 Wear rubber gloves as handling the lime/Portland mix is hard on the skin.
                              Kindled with zeal and fired with passion.

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                              • Ok so a local refractory supplier has castable for $30 for 55lbs didnt think that was a bad price so i picked that up and stainless steel fibers. I attached the product sheet. This company used to cast the ovens for chicago brick oven company you see their ovens online.. i plan om forming and casting this weekend hopefully tomorrow if I cam get the form made.
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