Wood sided bell?

I'm planning on a bell that will sit next to a batch box RMH.
The batchbox is to be contained in a 4 drawer file cabinet,  along with a water tank.
This first bell is gonna be small,  and the batch box will be 6 or 8", so I'm planning on a second bell next to it.
Rather than a steel bell with added mass,  I was thinking of  ramming cob into a wooden form.

So, would rammed cob work for a bell?
Would the inside form need to removed or could it be left in place and allowed to burn out?
Could the outside form be left in place or will the heat from the cob char the wood?
I'm not wedded to any if this,  for example I think any or all of the form could be made of steel instead of wood, but the idea of a wooden box of mud being the thermal mass intrigues me.

Tell me what y'all think...

Hi William,    As you may already know, the denser the material, the better the heat storage. A rammed cob bell should work just fine but would benefit from stuffing as much rock or dense material in there too. Saves a lot on mixing all that cob too.

I would say leaving the wooden form inside the bell would smoulder over a long period of time producing a lot of unwanted smoke more than just burning out and being done with it. Metal as a form material is pretty much a sure bet. An old washing machine frame or appliance is a great source for cheap or free metal.

The outside is hard to say what will happen to wood. An 8" batch is a beast so it seems likely that charring is a high probability. Monitoring the temps and see what is possible, but keeping a very close eye on it as soon as that cob dries! Wood also may not char right away until it gets to a critical dry point so I wouldn't feel overly safe with it unless the temps were low enough to easily touch at all stages of the burn.

Gerry,the cob is my way of making a cheap heat resistant seal but adding stones is a good idea.
Do you think I could use them inside the hollow space of the bell?
I'm thinking that would let me adjust the amount of mass.
Given what you have said, what do you think of using steel studs to build the frame of the bell, and cement backer board on the outside?
I know Portland can't take the heat on the inside of a bell,  but I think these fiber reinforced boards might be OK on the outside.
Inside,  I could skin the frame with sheet metal.
I could also use a 55 gallon steel barrel, a greater heater tank,  or a cylinder of sheet metal.

I'm not even sure the cob will need an inside mold.
I might be able to just slap the cob onto the outer walls.
Cob would probably stick well to expanded steel lathe, but I have a cheap source for backer board.
Even if I do need an inside mold, it doesn't have to be leave-in-place, and it probably should be built as lifts.
As I hash this out I think maybe I should work from the outside in, for ease of construction.

William Bronson wrote:I'm planning on a bell that will sit next to a batch box RMH.
The batchbox is to be contained in a 4 drawer file cabinet,  along with a water tank.
This first bell is gonna be small,  and the batch box will be 6 or 8", so I'm planning on a second bell next to it.
Rather than a steel bell with added mass,  I was thinking of  ramming cob into a wooden form.

So, would rammed cob work for a bell?
Would the inside form need to removed or could it be left in place and allowed to burn out?
Could the outside form be left in place or will the heat from the cob char the wood?
I'm not wedded to any if this,  for example I think any or all of the form could be made of steel instead of wood, but the idea of a wooden box of mud being the thermal mass intrigues me.

Tell me what y'all think...

That sounds painfully tight.

William,   Because the inside of the bell has fairly slow moving gases that are stratifying, adding mass inside can be done to a certain degree to increase the ISA of the bell without affecting free gas flow movement. I know columns are often used to do this which can be used to help support the roof of the bell if needed (ie. a wider bench) and to put as much of the mass at the top where its the hottest and therefore can extract more than at the bottom. So just throwing a bunch of bricks/rocks on the floor of the bell wouldn't store much heat.

I know Thomas Rubino used a backer board top on his bell. Perhaps he will chime in to tell you of his experience with it.
I think your ideas are on the right track. So many ways to make a form from different materials as long as they are matched to the use.
Do you know if the steel studs are galvenized? Not sure if they would be great right around the manifold area but may be fine elsewhere.
Hardware cloth or chicken wire is also a nice thing to use as it can be bent to almost any shape. To reinforce it, you could paper mache it to give it more stiffness if needed.  

You have a good point about it being cramped, let's examine the numbers.
The file cabinet is roughly 25.75 deep x 52.25 high x 15 wide.
An 8" batch box burn chamber is roughly 11.5" wide x 17.25" high x 23" long.

To the length we need to add the depth of the port and the OD of an 8" five minute riser, so the batch box is now 35" long.
Looks like we will either have to drastically shorten the burn chamber or let it stick out the front.

I'll assume a 2" deep refractory cement/rockwool/perlite base,  plus a scandalously short 24" tall heat riser, so 26" tall.
If we space the bottom of the water tank 6" from the top of the riser,  we'll have 32", leaving 20" or so for the water tank.
That's enough for me,  I plan on it being continuously refilled.
15"-11.5" is enough room for 1.75" thick sidewalls, but...
If I'm gonna let the burn chamber stick out the front ,  I could just thicken the side walls and make it big enough to set the file cabinet on top of as a bell.

A 6" batch box would be roughly 27.25" long including the port,  riser and burn chamber, so it still wouldn't fit, and I just remembered that a the kind of door I was planning on will add length to the build.

All of this points towards building a single bell custom sized bell instead trying to squeeze things into the file cabinet.
If anything,  the file cabinet would be better used if a second bell is needed.
Satamax,  thank you for your reply,  it lead me to work out my problems ahead of time!

The best reply i can give you, the cabinet is not gas tight either. So , to me, it sounds like a lot of work for not much gain. And lotsa pain!


Since i had the idea of using home heating fuel tanks, i'm a strong advocate for that technique.



Or may be where you are, agricultural tanks can be found.

The pic comes from that thread. https://permies.com/t/44806/Cobbling-workshop-heater-cooktop-oven Mind you, the start of the thread was pre five minute riser.


If you go for small footprint, and need a lot of isa.

A brick lattice could help a lot.



https://www.google.fr/search?q=brick+lattice&tbm=isch&ved=2ahUKEwi09Kig2-zrAhXJwoUKHTctDhYQ2-cCegQIABAA&oq=brick+lattice&gs_lcp=CgNpbWcQAzIECAAQEzIECAAQEzIECAAQEzIECAAQEzIICAAQBRAeEBMyCAgAEAUQHhATMggIABAIEB4QEzIICAAQCBAeEBMyCAgAEAgQHhATMggIABAIEB4QEzoGCAAQBxAeOggIABAIEAcQHlCMMljIP2DBSmgAcAB4AIABV4gB0AOSAQE2mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=toNhX7TBKcmFlwS32riwAQ&bih=616&biw=1280

HTH.

I've started my bell,  which I call a "dirty metal bell".
Scraps of sheet metal over steel studs,  filled with tamped earth.
The file cabinet, laid on its side, has become a platform to build on.

I've maxed out my firebox,  it will be 28.75" long inside, 125% of the  23" that is normal for an 8" batch rocket.
Because you need 2 inches infringe of and behind the fuel,  I should have space for 24" long fuel.

The footprint of the firebox  plus that of the riser , leave enough floorspace for the exhaust to exit into and through the file cabinet below.
From there it will go through a sheet metal "thimble" and into a chimney.

The rest of the cabinet will hold fire wood,  unless I convert it into a second bell.

Work continues on the bell.
There will be a 6 inch "cap" of tamped soil, with a stainless steel steam table pan set into it.
I'm thinking about including an oven right above the firebox.
If I do,  it will probably be a white oven, because making the oven gas tight seems easier than making the door gas tight.