web analytics
New member and first Portable 32" build - Forno Bravo Forum: The Wood-Fired Oven Community

Announcement

Collapse
No announcement yet.

New member and first Portable 32" build

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Hi Nate, by my calculations you'll need more.
    32" (813 mm) for simplicity let's just call it 80 cm diam. So R1= 40
    V1 (r40)= 4/3 x Pi x r3
    V1 = 268000 cc or 268 litres
    V2 (r45) = 381
    V2-V1 = 113
    but half because it's a hemisphere, so your dome volume is 56.5 litres
    as you get around 15 litres of wet castable per bag, you'll need 3.77 bags. As you'll also need more to cast the flue gallery you can probably say another bag, depending how thick you make the casting. So that brings it to 5 bags. I think you'll need to go back and get another three bags.

    check my calculations "measure twice cut once"

    Here's a good thread to follow https://community.fornobravo.com/for...and#post396954

    For a one off cast the extra trouble and work required to do a multi piece casting is not worth it IMO a one piece casting works fine. The main advantage of a multi piece casting is that the pieces are more easily moved, but if you cast in situ then you don't have to move it.
    Last edited by david s; 09-29-2017, 03:38 PM.
    Kindled with zeal and fired with passion.

    Comment


    • #17
      Originally posted by david s View Post
      Hi Nate, by my calculations you'll need more.
      32" (813 mm) for simplicity let's just call it 80 cm diam. So R1= 40
      V1 (r40)= 4/3 x Pi x r3
      V1 = 268000 cc or 268 litres
      V2 (r45) = 381
      V2-V1 = 113
      but half because it's a hemisphere, so your dome volume is 56.5 litres
      as you get around 15 litres of wet castable per bag, you'll need 3.77 bags. As you'll also need more to cast the flue gallery you can probably say another bag, depending how thick you make the casting. So that brings it to 5 bags. I think you'll need to go back and get another three bags.

      check my calculations "measure twice cut once"

      Here's a good thread to follow https://community.fornobravo.com/for...and#post396954

      For a one off cast the extra trouble and work required to do a multi piece casting is not worth it IMO a one piece casting works fine. The main advantage of a multi piece casting is that the pieces are more easily moved, but if you cast in situ then you don't have to move it.
      Again thank you David, I have 3 bags to start and looks like ill have to go back to get more to do the gallery, at least its close! I was thinking of casting in place but i was thinking if i section it, then there are pre existing weak points for thermal expansion and contraction during firings. I didn't want it to crack all crazy on the inside. Or is that unlikely as its isn't that big a structure?

      Kind Regards,

      Nate

      Comment


      • #18
        If you cast it in one piece you will get some hairline cracks. My oven here at home is a one piece dome, is about 9 years old and the hairline cracks haven't got any bigger. I should think the oven will outlast my grandchildrens lifetimes. My mobile oven which I built around the same time (see in mobile deconstruction under other oven types) did have a larger crack at the back, but it got an absolute flogging from customers over firing and very frequent use. As it is my demonstration oven it needs to maintain a "newish" look. I still don't think it's worth casting in sections for a one off. I do now cast my ovens in three sections, but it took a lot of work adapting the mould. The big advantage is that a three piece dome is way easier to move than a single section.
        Kindled with zeal and fired with passion.

        Comment


        • #19
          Originally posted by david s View Post
          If you cast it in one piece you will get some hairline cracks. My oven here at home is a one piece dome, is about 9 years old and the hairline cracks haven't got any bigger. I should think the oven will outlast my grandchildrens lifetimes. My mobile oven which I built around the same time (see in mobile deconstruction under other oven types) did have a larger crack at the back, but it got an absolute flogging from customers over firing and very frequent use. As it is my demonstration oven it needs to maintain a "newish" look. I still don't think it's worth casting in sections for a one off. I do now cast my ovens in three sections, but it took a lot of work adapting the mould. The big advantage is that a three piece dome is way easier to move than a single section.
          Hey David, by the time i had read this i had already geared up for sectioning it into three pieces plus gallery. I kinda thought you would say sectioning is best. Last night i "poured" my first section and it took probably 1.5 bags, so i think your right on the 5/6 bag estimate. First pass i had a little bit of slump which i rectified quick smart (just fraction to wet) second pass was perfect. The thickness is basically uniform. 2.5-3 inches at the top and bottom and one side a little light on 1.75 inches so it will get a top up as i put it all together.

          I will cast the second section tonight after i sleep (night shift last night)

          Side note, there are no burn out fibres in this mix but the company says it the one they use for making their pizza ovens so should be ok i think??

          cheers Nate

          Comment


          • #20

            Comment


            • #21

              Comment


              • #22
                Thought i might post an update. DavidS you were right, five bags it is had to go back and pick up another two. So the casting of the main dome is all done, except the keystone piece at the top and has set hard a a rock! I cast into three pieces. The pieces fit perfectly together which is nice, I made two errors though, neither fatal just annoying. First the base of the dome on the front section is a fraction wider than i wanted and doesn't sit on the firebricks on either side. I have include pics for you to see. i was thinking of when i bed the dome in with a wet slurry of the concrete i might make a smooth buttress on the inside to cover the vermicrete thats exposed? what do you think? would that work or would it crack off?

                Second mistake was i think the front section hasn't allowed enough room for a gallery of sufficient size to accomodate a 6" flue. I either have to cut into the dome or extend the gallery... unless a 5" flue will suit this size oven? Any advice would be appreciated

                Pretty stoked overall how its come up. It looks the part so far at least anyways

                Cheers Nate
                Last edited by NateQLDer; 10-06-2017, 12:15 AM.

                Comment


                • #23
                  If you want to add any more castable to existing cast, do it asap while there is still moisture in the casting. Also to assist bonding, sieve out the coarse aggregate from some castable and make a thin slurry with it to coat the area you want to add more castable onto, just prior to adding the fresh castable. This will help the bond.

                  Regarding the gallery issue you can push the gallery further over the oven entry which allows you to accomodate the flue but keeps the entry shallow. The pic on this post should explain what I mean, if the attached pics don't.

                  2
                  You need a 6" flue for your sized oven, but another solution would be to bend the bottom of the pipe into an oval so it has less depth.


                  Click image for larger version  Name:	P6160027.jpg Views:	2 Size:	410.7 KB ID:	401680Click image for larger version  Name:	P6160030.jpg Views:	2 Size:	523.6 KB ID:	401681
                  Last edited by david s; 10-06-2017, 03:40 AM.
                  Kindled with zeal and fired with passion.

                  Comment


                  • #24
                    Originally posted by david s View Post
                    If you want to add any more castable to existing cast, do it asap while there is still moisture in the casting. Also to assist bonding, sieve out the coarse aggregate from some castable and make a thin slurry with it to coat the area you want to add more castable onto, just prior to adding the fresh castable. This will help the bond.

                    Regarding the gallery issue you can push the gallery further over the oven entry which allows you to accomodate the flue but keeps the entry shallow. The pic on this post should explain what I mean, if the attached pics don't.

                    2
                    You need a 6" flue for your sized oven, but another solution would be to bend the bottom of the pipe into an oval so it has less depth.


                    {"alt":"Click image for larger version Name:\tP6160027.jpg Views:\t2 Size:\t410.7 KB ID:\t401680","data-align":"none","data-attachmentid":"401680","data-size":"small"}{"alt":"Click image for larger version Name:\tP6160030.jpg Views:\t2 Size:\t523.6 KB ID:\t401681","data-align":"none","data-attachmentid":"401681","data-size":"small"}
                    Awesome idea with the flue! I think the link to your deconstructed one really helped! I will start to design the mould tomorrow As for the adding of cement... Well i tried the next day and it was like a rock, all mix even thin slurry just seemed to fall off. I even tried roughening up the surface with a grinder but no avail. Its only one of the sections and only one small bit that just under the 2inches think so will have to do i hope. I learnt my lesson for the remaining castings though and the thickness is good, too thick perhaps. The front casting is easily 3" in spots haha. What would you suggest for the exposed vermicrete though? should i just cover with a coat of cement and bed the dome in? could i make a buttress around the inside? I don't know considering the fact that the cement won't stick to hardened cement ....

                    Sorry one more question, Should i use high temp motor to join the sections of the dome?or just push them together? they fit snugly

                    Cheers for all the advice i really appreciate it

                    Comment


                    • #25
                      Vermicrete won't stand up to the intense heat in that position. Covering it with a thin layer of castable probably won't suffice either. If it were mine I'd dig out least an inch of the vermicrete and replace it with castable. As you don't want any bits falling on your food I'd suggest you only fill the joins between the castings from the outside. Again, presuming you have some castable left, the sieved mix makes a very good high temp mortar.
                      Kindled with zeal and fired with passion.

                      Comment


                      • #26
                        Thanks again David , good idea about digging out the vermicrete, will be a suitable pain in the ass to cut out but necessary . I have a bag of high temp motor and will use that from the outside when i have finished adding the necessary refractory. Still have 3/4 of bag refractory cement so i should have enough for the flue plus the bits to fix the exposed vermicrete. Will post pics when i finish those bits

                        Comment

                        Working...
                        X