FINALLY!!! - Start Of Building My Oven

[david s]

Re: FINALLY!!! - Start Of Building My Oven

Ask your supplier of the needles if they are stainless. If they were very expensive then they probably are. Stainless does not rust easily. Leave a few in a white dish outside and put some water with them. Can you estimate the weight of your oven then give it to your stand manufacturer and hope he knows what he's doing. I used 75 mm thick Hebel (aerated concrete) for my mobile base. It is reinforced with steel cast into it and it weighs 1/3 that of ordinary concrete. It is also a very good insulator, but I think your plan of steel and insulating board should work ok too.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

Thanks, I'll ask my supplier to make the stand as sturdy as possible.

Maybe I can make a thin 1" layer of aereated concrete to give it stability.

My concern at the moment is if I just build the oven over a metal sheeting, there's risk of heat loss or correct me if I'm wrong?

I hope to finish the last piece of the cast this weekend so will get my supplier to manufacture the stand soon.

Thanks
Regards
OM

[david s]

Re: FINALLY!!! - Start Of Building My Oven

Yes, the heat will be attracted to the steel which is a netter conductor. On my mobile the supporting slab made of aerated concrete sits in a steel cradle and the steel gets a lot hotter than the aerated concrete.even though it is further away from the fire. Just insulate well and you'll be ok.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

I'll make sure the base of my oven sits on atleast 3 inches of Ceramic Board.

Since I'm onto my last dome piece, I started thinking of the next steps to follow and the Vent Design came to mind.

Now I've briefly read about the design of the vest and there's so many questions I've come across, like dimensions, round, square or rectangle, metal or cement and I can't seem to answer these question myself so I need some advice from you pro's out there.

1) What shape do u suggest I make my vent to allow for best flow of smoke out the oven and basically best effeciency of a vent? Above my oven opening, it's shaped in an arch form to the centre of the oven dome so the vent needs to sit flush against this arch form.

2) I prefer a refractory casted vent for heat retention purposes or a metal vent for purpose of weight reduction. Any suggestions?

3) Based on my oven size of 24", height of 13", what dimensions do you suggest my Vent be and what diametre do you suggest my flue be?

Once my 4th dome piece is complete, I will put them together on the ground and take some pictures just so you guys get an idea of my dome design and then you'll will be in a better position to advice but for now can you make suggestions on what's explained above.

David, just before posting this, I came across this link by James http://www.fornobravo.com/forum/f8/o...-size-692.html regarding opening height of the oven. James mentioned somewhere in the post that he once made a 26" oven with a opening width of 16" and height of 10", very similar to mine. He said that heat just wouldn't hold with these dimensions. Now I'm a little concerned and was contemplating whether to add the extra inch over the current dome piece before I put it together or shall I build the entire oven and see how it goes but my question is will I be able to add the extra inch later after completion.
James, if you're reading this, maybe you can comment as well?

Thanks
OM

[david s]

Re: FINALLY!!! - Start Of Building My Oven

Hi OM my oven is about the same size as yours, in fact a little smaller at 21" internal diam. also cast. I decided to make the vent piece as thin as I dared because I didn't want it to sap heat from the oven. It only weighs 8 Kgs. and funnels gently to a circle slightly larger than the 125mm (5") diam stainless flue. My flue entry is also only 5" deep and 17" wide. This is quite wide for an oven so small, but the wide yet shallow entry makes for really easy operation to easily reach into the oven, although it must increase the heat loss. I think it has good heat retention and the oven does not have lots of smoke staining on the front of the outer arch. It draws really well and does not smoke up.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

Hi David

I'm trying to picture your oven vent based upon the dimensions you've given but i cant do justice in my head.

Any chance you have a picture of the vent showing the flue as well.

My flue is also only 5" deep and 17" wide.

I'm guessing you meant you oven opening is this dimensions as i cant picture your flue being 17" wide. If the opening is what you were referring to, than 5" for height is quite low or am i still misunderstanding you. By the way, was the picture you posted that of your oven opening?

It only weighs 8 Kgs. and funnels gently to a circle slightly larger than the 125mm (5") diam stainless flue

WOW! 8 KG Vent, that must be super thin. I'd definitely keep that in mind though i wouldn't dare try going so thin but i will not make it too thick either.
You also mention your vent funnels gently into a slightly larger circle than 5". I'm guessing the diameter of the circle closest to the bottom of the vent is larger and the the portion closest to the top of the vent where the flue fits into place is 5". Any particular reason for this as I would definitely keep this in mind and probably end up doing the same.
From my minimal knowledge of this subject, my theory is as follow. A larger diameter at the bottom of the vent allows more smoke to gather while traveling up the vent to the flue, the narrowing of the diameter doesn't allow the smoke to escape to quickly so enabling better heat retention. This is probably just some silly theory from mine, I'm sure there's another explanation.

Thanks
Regards

[david s]

Re: FINALLY!!! - Start Of Building My Oven

Maybe this photo will explain how I've done it. Because the vent piece is so light and thin I've added buttresses on the sides for strengthening. SS needles added to the castable for reinforcing too.The previous pic I posted was of the outer arch, the vent piece and the inner dome.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

Thanks David

I'm leaning towards your design. I'm still torn between a Metal Fabricated Vent or Castable.

Quote:
My flue is also only 5" deep and 17" wide.
I'm guessing you meant you oven opening is this dimensions as i cant picture your flue being 17" wide. If the opening is what you were referring to, than 5" for height is quite low or am i still misunderstanding you. By the way, was the picture you posted that of your oven opening?

Is this referring to your Opening or Flue?

Regards
OM

[david s]

Re: FINALLY!!! - Start Of Building My Oven

"My flue is also only 5" deep and 17" wide."
Sorry , this should read flue entry. I shall amend the post.

[david s]

Re: FINALLY!!! - Start Of Building My Oven

OM I've seen lots of oven designs that do not have any "funnelling" to the flue and they all have smoke staining on the front arch. My reason of making the diameter of the entry piece slightly larger than the flue diam. was because the second design I tried had the flue cast directly around the flue and when the flue expanded with the heat it cracked the casting.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

Hi Guys

My last dome piece was delayed this week due to some unforeseen circumstances.
I hope to complete the last piece by next weekend at the latest.

There's still a lot of uncertainty with my Vent Design. What I am sure about is I'm most definitely going to use David's design. Where the most part of the uncertainty comes about is whether to Cast it from Refractory Cement or fabricate it from Metal.

Both have their Pro's and Cons but the 1 Pro I've found with the Metal vent or I should say I assume its a pro. Using a metal vent will draw less heat from the oven as a Castable vent will continue drawing heat until it reaches it optimum temperature while metal will reach that temperature much quicker and thus the oven will continue to stay hotter.

Anyone has some advice on this theory and Metal Vents in particular?
Could you also list some Pro's vs Con's on each of the above mentioned materials?

Thanks
Regards
OM

[dmun]

Re: FINALLY!!! - Start Of Building My Oven

Metal's a big category. Could be anything from flimsy sheet metal to a massive iron casting. Remember: flue gasses are corrosive, so if you're going with sheet metal, I'd go with something heavy gage, and, for preference, stainless.

[Oven_Man]

Re: FINALLY!!! - Start Of Building My Oven

Thanks for that Dmun, i never really realized how much "Red Tape" a metal vent would have, so i guess I'm sticking to a Casted Vent.

Just how thin can i make my vent.

Lastly, i just cant get my head around this but my oven is obviously rounded and for the vent to fit flush against the top of the oven entrance, it would need to have the same curved shape, almost like puzzling it in.
Simply, how can i do that and do i need to do that and if not, would a load of Mortar "slapped" both against the vent and entrance be sufficient and strong enough to keep the vent up there, considering this oven will be mobile.

Thanks
Regards
OM

[dmun]

Re: FINALLY!!! - Start Of Building My Oven

I'm the wrong person to ask castable refractory questions. Maybe someone else will jump in. My guess, for what it's worth, would be to cast it in place, rather than try to engineer forms to fit your various curves.

[david s]

Re: FINALLY!!! - Start Of Building My Oven

I suggest you assemble your pieces on the oven floor and build a sand mould against the entry, cover it with strips of wet newspaper, then cast onto it.