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30" cast dome design

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  • #31
    How do people know the height of a chimney? I know it depends on a lot of factors... but where do you start? I need to order vent/chimney components but I don't know whether I should go 2', 3' or 4' high/long? I would greatly appreciate an advice on what to order, please! It is a 30" oven and, in case it matters, it will be standing in my yard on that wooden stand in the picture below.

    Edit: Forgot to mention... I am reluctant to go high unless necessary because I am planning to make a cover for the oven to protect from the weather. Much easier to put a cover on if the chimney is 2' instead of 4... but then again if it does not provide sufficient draw that is even worse. Thanks!
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    Help, please!!! Cheers!
    Last edited by sergetania; 07-23-2020, 06:21 PM.


    • #32
      Another step has been completed! Time to actually start on the oven itself. Looks like a clean slate to me!

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      • #33

        Does the attached drawing of the dome/gallery footprint including the sizes make sense? I think I got it right... hopefully. The sides of the gallery don;t look parallel on the picture but they are on the drawing. The length(depth) of the gallery will depend on the size of the chimney adapter, probably no more than 10" (waiting for an order from Forno Bravo that includes insulation boards so drawing on the concrete).

        Also, here is my math.

        30" internal diameter 2"-thick dome with an entrance gallery about a foot high, foot long and 1 1/2' wide

        The dome 17" radius volume minus 15" radius volume = 6442 cubic inches = 3.73 cubic feet divided by two roughly = 1.9 cubic feet + 1 cubic feet for the gallery = 3 cubic feet of castable material

        KS4 Plus (by Harbison Walker) 3 cubic feet x 122 lbs/cubic ft = 366 lbs of dry mix (will probably get 7 x 55 = 385 lbs or 8 bags - 8 x 55 lbs = 440 lbs).

        Did I make any mistakes? Using inches and feet do not help, not at all
        Thanks for help!

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        • #34
          I am going to defer to David since he is our cast expert.
          Google Photo Album []


          • #35
            Regarding your flue pipe height, a taller pipe will give you greater draw, but you only need go high enough to get the smoke away from your face. The usual height is 3' and will stand up ok on its own. That is it does not require any extra support higher up. They usually come with crimped ends allowing another section to be easily added if required. For your oven size you need a 6" diameter.
            Your plan looks fine, that product should contain the burnout fibres so you don't need to go out and buy them specially.
            It is far easier to cast the dome with an oven mouth plate set in place, then remove it when the cast has set, then make the flue gallery mould in front of the oven mouth. This method also makes a better rebate for the oven door to sit against. As it is a more tricky part of the design, you will be more experienced at laying up the refractory mix, making doing it a second time easier.

            Nice start by the way.

            Some good info on the attachment for you.

            Instructions for the use of Castables .docx
            Attached Files
            Last edited by david s; 07-28-2020, 05:03 PM.
            Kindled with zeal and fired with passion.


            • #36
              David, thank you and thank you! Huge help from you and the forum!
              I saw the instructions you posted earlier. It's good to understand what needs to be done. Love the throw-ball-up method.
              I will add stainless steel needles to the mix, just because I can. Also,the decision on whether to cast the gallery separately will depend on a small experiment I would like to conduct with constructing a form for the dome. You will probably dismiss it as too much efforts but I am not concerned with efficiency or lack of thereof. Also, I am honestly afraid of connecting separate dome and gallery. Concrete is a still foreign material for me...though I love how amazingly smooth that countertop turned out - strange you can make something like that out of concrete. Fun to draw with a sharpie on it!


              • #37

                Today I have practiced casting (more about it in a separate thread). What I learned? It's not easy especially when a form is more complex than a simple sphere. I'd stay stressful,at least for the first time. Also, I am not sure I can accurately estimate how much concrete I will use. It goes quickly. The decision - I will cast the gallery separately as you advised.

                So how do I split the dome and gallery in two? At the line where the door is,the rebate for the door?




                • #38
                  Yes there. Regarding arsenal, I think the preppers, particularly in the US are enjoying their arsenals.
                  Last edited by david s; 08-01-2020, 10:03 PM. Reason: Typo
                  Kindled with zeal and fired with passion.


                  • #39
                    Oh, the preppers! Got me a bit confused with the original version!

                    ​​​​​​I hope they are enjoying being prepped when something has actually happened... unless there's always next level you need to prepare for so no time for enjoyment!


                    • #40
                      Given my original desire to build an oven using an exercise ball and a skill set of my assistant, we have decided to make a paper mache (always hated it in kindergarden!) for the dome form. I hope it works. It seems to be strong enough to hold two bags of concrete on top and, hopefully, I will be able to remove it from inside of the dome when done. I will wrap it with syrene wrap before casting. Need to attach a form for the entrance and then wish me luck!
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                      • #41
                        The floor looks great and the paper dome very precise! How do you plan to remove it though?
                        My cast oven build thread



                        • #42
                          Ha! Great question! We will find out! Absolutely worst case scenario,it will have to burn. I hope I can cut through it with metal snips, bend and remove it, piece by piece. It's not thick, less than 1/4 inch. If I can remove material along the buttom, it should drop down. Also, since i am planning to cast the entrance separately, I will have an easier access to the inside of the dome.


                          • #43
                            5 hours of thumping handfuls of concrete onto a dome! Supposedly, this is my idea of fun. But we got it done right before it got dark. I hope it looks decent inside. I will try to remove the form tomorrow. Fingers crossed.

                            Did I mention I now have a lot of appreciation for people who do masonry for living!
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                            Last edited by sergetania; 08-25-2020, 10:09 AM.


                            • #44

                              david s I have a question. The easiest for me is to mount the form for the entrance next to the dome and cast the entrance in place. The form is made of polystyrene so I should be able to drill it out with a Forstner bit. Any problems with casting the entrance in place? Thank you!
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                              Last edited by sergetania; 08-25-2020, 04:23 PM.


                              • #45
                                Looks like really tidy work sergetania ! Great job
                                My cast oven build thread