#21  
Old 12-30-2011, 10:49 AM
Archena's Avatar
Il Pizzaiolo
 
Join Date: Apr 2007
Location: Alabama
Posts: 1,214
Default Re: Rocket cob oven

Try looking for rocket stoves as heating- I've seen it combined with cob that way.

I'm sick as a dog right now but if you don't find anything let me know and I'll hunt down a link or two when I'm better.
__________________
"He is no fool who gives what he cannot keep to gain what he cannot lose." - Jim Elliot

"Success isn't permanent and failure isn't fatal." -Mike Ditka
[/CENTER]
Reply With Quote
  #22  
Old 12-31-2011, 12:31 AM
Peasant
 
Join Date: Dec 2011
Location: Auckland
Posts: 28
Default Re: Rocket cob oven

I did manage to find this; Rocket Oven.mov - YouTube
Its a bit long winded but there are some very interesting ideas in there.

Building all the nuts and bolts out of clay sounds like fun BUT theirs is tiny. If anything cracks they can just lift the whole dome off or knock out some bricks at the bottom and they have access to everything. A decent size oven would need proper foundations and getting access for repair job could be a nightmare. Plus I want everything to look closed in, just like a normal oven.

At some point they comment that the bottom of their pizzas were getting burnt, so they had to reduce oven temperature and take almost 5 mins to cook their pizzas. I think this is because all their heat is going direct to the underside of the hearth. It shouldn't be a problem if I just use the rocket for original heating and still have a normal fire inside the dome as well.

Also, take note cobbers; they add sugar or potash to make their clay more workable. I hadn't heard of that technique before.

Anyway I was very impressed with what they managed to do with basic materials. Looking forward to your observations.
Reply With Quote
  #23  
Old 12-31-2011, 09:01 AM
Journeyman
 
Join Date: May 2009
Location: Detroit
Posts: 400
Default Re: Rocket cob oven

The oven in the video does look pretty similar to what you described. By constricting the rocket exhaust to the rear of the oven and venting out the front I think you will get better performance then they do. I'd also go with a very low dome because odds are you are still gonna lack top heat, but it will turn out a much better pizza then a home oven. You should look at the little black eggs people build from old weber grills. The heat source and materials are very different, but the path of the fire and heat through the oven is exactly what you proposed. You will find they struggle with top heat, but with enough tweaking do work good enough to produce a 2 or 3 minute pizza.
Reply With Quote
  #24  
Old 12-31-2011, 11:03 AM
Archena's Avatar
Il Pizzaiolo
 
Join Date: Apr 2007
Location: Alabama
Posts: 1,214
Default Re: Rocket cob oven

Rocket Stoves

Homegrow Evolution

Design Tool - Firefox Only

This should be the one you need:
Rocket Baking Oven Construction Manual (PDF, 1.6MB)
__________________
"He is no fool who gives what he cannot keep to gain what he cannot lose." - Jim Elliot

"Success isn't permanent and failure isn't fatal." -Mike Ditka
[/CENTER]

Last edited by Archena; 12-31-2011 at 12:12 PM.
Reply With Quote
  #25  
Old 01-01-2012, 10:23 AM
Journeyman
 
Join Date: May 2009
Location: Detroit
Posts: 400
Default Re: Rocket cob oven

That design is for a very basic white oven, as is every other design I've seen for rocket stove ovens which generally use metal drums. I don't think that is what the people in this thread are looking for, and I certainly don't see it producing pizza any better then a home oven if that is the goal.
Reply With Quote
  #26  
Old 01-01-2012, 10:50 AM
Archena's Avatar
Il Pizzaiolo
 
Join Date: Apr 2007
Location: Alabama
Posts: 1,214
Default Re: Rocket cob oven

Um, yeah - the advantage to a rocket stove is that it uses relatively little wood. In places where wood is scarce that's extremely important. It wouldn't be better than a black oven or another white oven - it's only advantage is fuel consumption.

I suspect an off center configuration would be better. I don't see any way to not have a hot spot so the better bet is to make that work for you. I'd put the hot spot to the back where the fire would be in a black oven. I'd also mark it in some way so I knew where it was for certain. The oven should work normally and you don't have to cook around a big hot spot in the middle. (Hmm, maybe to the side would be better - it could be used for searing and other really fast cooking...)

If working time isn't at issue, anything they did in brick can be done in cob - it's just no where near as fast. I'd also leave an access (unmortared brick, maybe) to the open section under the hearth. If the rocket stove doesn't work out, insulating that section would be simple and you'd have a standard black oven.

Hmm, you could probably substitute a chimney flue for the brick upright chamber...
__________________
"He is no fool who gives what he cannot keep to gain what he cannot lose." - Jim Elliot

"Success isn't permanent and failure isn't fatal." -Mike Ditka
[/CENTER]
Reply With Quote
  #27  
Old 01-01-2012, 10:12 PM
Peasant
 
Join Date: Dec 2011
Location: Auckland
Posts: 28
Default Re: Rocket cob oven

Most of this video here Permaculture Our Urban Design Part 7 - Rocket Oven Pt1 - YouTube is not really of interest to me but at the 8-9 min mark he shows how hes attaching the rocket stove to the oven.
He uses an cradle slung underneath the main horizontal slab (the base of the hearth) with adjustable screw thingies, I cant remember what they're called. If you already have a woodbox space underneath it would be a very simple matter to remove the cradle and access everything for repairs. To me, that tiny bit of genius made watching all 20 minutes (part 1 and 2 : O) worthwhile.

With this cradle design in mind, I think my plan of attack to make the chambers of the rocket part would be to either use chimney flue covered in cob or cast something out of perlcrete.

Regarding the hot spot, I think a combination of a flared opening under the hearth, a ceramic deflector sitting on top of the opening and the metal base to the firebrick hearth should help to distribute the heat evenly. And as you point out Archena, a hot spot can be put to good use...
Reply With Quote
  #28  
Old 01-01-2012, 10:43 PM
Peasant
 
Join Date: Dec 2011
Location: Auckland
Posts: 28
Default Re: Rocket cob oven

Also, if anyone does take the time to watch that (and part 2), I was very surprised he could only get it to 250 degrees C.

First of all let me state that I only intend to use the rocket part as a turbo, to speed heating and to increase my overall fuel efficiency. I will still have the main fire going up top.

However, I expected a bit more grunt from the rocket. Something that maxes out at 250 C would hardly be worthwhile. From what I've seen in other videos Rocket Oven.mov - YouTube they can do much better, apparently getting up and over 750 degrees C.

I will take a few guesses as to why his didn't work too well. Please feel free to shoot me down (you won't even have to watch the video for this) and to come up with suggestions of your own.

1) Chimney in the centre of dome. Most ovens have them at the front. Given that heat rises, wouldn't the hottest air be escaping if the hole is at the top?

2) Deflector plate at bottom of chimney made of tin. Seems like this would do little to reduce heat transfer up the chimney (such a good conductor) and would reduce draft.

3) Too small an intake for the rocket.

4) Small thermometer about 3/4 up the dome and a paver instead of a firebrick hearth. The heat is concentrated at the bottom of a rocket oven anyway, but because he has an ordinary paver for a hearth I think this problem is compounded because the paver is not absorbing and radiating the heat properly. That paver could be scorching hot and he'd never know until his veggies caught fire.

Anyway. Thats my 2 cents. Looking forward to reading a more educated analysis.
Reply With Quote
  #29  
Old 01-02-2012, 09:42 AM
Archena's Avatar
Il Pizzaiolo
 
Join Date: Apr 2007
Location: Alabama
Posts: 1,214
Thumbs up Re: Rocket cob oven

Quote:
Originally Posted by arthuritus View Post
Most of this video here Permaculture Our Urban Design Part 7 - Rocket Oven Pt1 - YouTube is not really of interest to me but at the 8-9 min mark he shows how hes attaching the rocket stove to the oven.
He uses an cradle slung underneath the main horizontal slab (the base of the hearth) with adjustable screw thingies, I cant remember what they're called. If you already have a woodbox space underneath it would be a very simple matter to remove the cradle and access everything for repairs. To me, that tiny bit of genius made watching all 20 minutes (part 1 and 2 : O) worthwhile.

With this cradle design in mind, I think my plan of attack to make the chambers of the rocket part would be to either use chimney flue covered in cob or cast something out of perlcrete.

Regarding the hot spot, I think a combination of a flared opening under the hearth, a ceramic deflector sitting on top of the opening and the metal base to the firebrick hearth should help to distribute the heat evenly. And as you point out Archena, a hot spot can be put to good use...
Sounds good!

Do you have "Earth Ovens"? It has a chapter on insulating with cob that would probably be of interest.
__________________
"He is no fool who gives what he cannot keep to gain what he cannot lose." - Jim Elliot

"Success isn't permanent and failure isn't fatal." -Mike Ditka
[/CENTER]
Reply With Quote
  #30  
Old 01-02-2012, 09:54 AM
Archena's Avatar
Il Pizzaiolo
 
Join Date: Apr 2007
Location: Alabama
Posts: 1,214
Default Re: Rocket cob oven

Quote:
Originally Posted by arthuritus View Post
Also, if anyone does take the time to watch that (and part 2), I was very surprised he could only get it to 250 degrees C.

First of all let me state that I only intend to use the rocket part as a turbo, to speed heating and to increase my overall fuel efficiency. I will still have the main fire going up top.

However, I expected a bit more grunt from the rocket. Something that maxes out at 250 C would hardly be worthwhile. From what I've seen in other videos Rocket Oven.mov - YouTube they can do much better, apparently getting up and over 750 degrees C.

I will take a few guesses as to why his didn't work too well. Please feel free to shoot me down (you won't even have to watch the video for this) and to come up with suggestions of your own.

1) Chimney in the centre of dome. Most ovens have them at the front. Given that heat rises, wouldn't the hottest air be escaping if the hole is at the top?

2) Deflector plate at bottom of chimney made of tin. Seems like this would do little to reduce heat transfer up the chimney (such a good conductor) and would reduce draft.

3) Too small an intake for the rocket.

4) Small thermometer about 3/4 up the dome and a paver instead of a firebrick hearth. The heat is concentrated at the bottom of a rocket oven anyway, but because he has an ordinary paver for a hearth I think this problem is compounded because the paver is not absorbing and radiating the heat properly. That paver could be scorching hot and he'd never know until his veggies caught fire.

Anyway. Thats my 2 cents. Looking forward to reading a more educated analysis.
Unedumacated analysis:

From what I've read a true white oven shouldn't have a chimney at all. I suspect all of your objections have merit but that #1 is the primary culprit. No ovens are built with the chimney centered - at least none I can find (and around here it'd be the first thing people would try talking you out of). Tin or otherwise, no deflector would overcome the heat loss - the best it could hope for would be to slow it down a little.

If I were him, I'd stuff an insulating blanket in the flue and see what happens. I suspect he'd be filling in the chimney a short while later...
__________________
"He is no fool who gives what he cannot keep to gain what he cannot lose." - Jim Elliot

"Success isn't permanent and failure isn't fatal." -Mike Ditka
[/CENTER]
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Why Italian Wood-Fired Ovens are Round james Newbie Forum 50 04-01-2014 10:14 PM
FINALLY!!! - Start Of Building My Oven Oven_Man Pompeii Oven Construction 249 03-14-2013 06:33 AM
Tuscan and Naples designs james Pompeii Oven Construction 5 09-11-2011 05:53 PM
Oh no - my oven is wet PizzaArthur Firing Your Oven 36 11-23-2009 10:16 PM
Neapolitana Style Oven (31.5") southpaw Pompeii Oven Construction 4 08-11-2007 07:29 AM


All times are GMT -7. The time now is 09:43 AM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC