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Mobile rocket cob oven - weight and strength considerations  RSS feed

 
pollinator
Posts: 177
Location: Ashhurst New Zealand
25
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Hi combustion gurus! I'm cogitating over the design of a mobile oven that will serve a few functions:

1) The cob dome build will comprise the practical segment of a PDC module on building materials and techniques;

2) Our community resilience group will assume ownership of the oven and use it for pizza parties and events;

3) The documentation of the process will serve as an ongoing educational resource.

My basic plan is a 6" burn chamber constructed with firebrick splits, perlite and clay insulation for the riser, a refractory oven bottom (either splits or cast, haven't decided), and a dome of cob with goodly amounts of sawdust for insulation. The base and enclosure could be just about anything durable, and I'm weighing up the merits (see what I did there?) of a masonry shell, a timber frame, or a metal structure. The unit needs to be able to go places on a trailer, and my preference would be to permanently mount it on a little single-axle job. How sturdy do you think this base structure needs to be, and what balance needs to be achieved in terms of securing it to the trailer frame and isolating the masonry and cob elements from shock and bouncing in transit?

A timber or metal frame fixed to the trailer frame could incorporate some compression springs, or the whole thing (regardless of base construction type) could rest on a platform that sits on base isolators and relies on guy wires or similar to control pitch and sway. Thoughts? I'll try and get a drawing up in days to come, but really slammed with work this week so not right away.
 
pollinator
Posts: 1947
Location: Cincinnati, Ohio,Price Hill 45205
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Must it be be cob? A derelict wall oven can be converted to be heated by a rocket.
 
Phil Stevens
pollinator
Posts: 177
Location: Ashhurst New Zealand
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Yes, if you refer to the listed functions, the material is in the requirements. We like to have real world applications in the practical component.
 
gardener
Posts: 2581
Location: Upstate NY, zone 5
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I think a metal frame to enclose all the cob elements would be most practical and durable. Timber, no matter how well built, might flex a bit in transit, and any flexure at all will be detrimental to the cob. Metal would also be the lightest way of building it solidly. I think you would want it overall as low as possible to reduce transit shocks. Perhaps mount the bottom of the combustion chamber behind and a touch below the axle (whatever is required for ground clearance).
 
Phil Stevens
pollinator
Posts: 177
Location: Ashhurst New Zealand
25
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@Glenn, my gut said a welded or bolted steel frame would be the best choice. The project has now gone off the boil since no one has put their hand up to own/register/house the trailer, but I'll have a chat with a local fabricator to get his thoughts.

Thanks for your input.
 
This cake looks terrible, but it tastes great! Now take a bite out of this tiny ad:
five days of natural building (wofati and cob) and rocket cooktop oct 8-12, 2018
https://permies.com/t/92034/permaculture-projects/days-natural-building-wofati-cob
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