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Post by patamos on Oct 17, 2014 20:48:03 GMT -8
Maybe the L-feed also took off more/sooner due to its portability and potentially lower cost/effort in construction. All happening in about the size of a bucket...
I got into them as cookers because i bought into the Aprovecho literature on having the heat riser as short as (reasonably) possible so as to get as much heat as possible to the pot. Seems a few people in the forum have mentioned accessing more BTUs this way.
Still, ergonomics say the J-feed is the winner.
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Post by Daryl on Oct 18, 2014 0:05:43 GMT -8
Well, I'm eagerly awaiting your build, patamos. Good luck.
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Post by patamos on Oct 18, 2014 6:25:35 GMT -8
Apologies for my sprees of geekyness, but i am truly curious as to why the wet wood in Kari's example burns better in the J. Is it entirely a matter of a relatively longer heat riser? Or is there something about how the stack of wood keeps dropping into an ideal zone? Or...?
well being
pat
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Deleted
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Post by Deleted on Oct 18, 2014 7:17:02 GMT -8
A J-feed preheats the air.
The wood at the back or above the burn zone can get dryer.
More turbulence is created.
And finally it is more fool proof.
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Post by patamos on Oct 18, 2014 9:49:54 GMT -8
Thanks Kari, Crystal clear as always  |
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gjh42
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Post by gjh42 on Oct 30, 2014 14:05:32 GMT -8
It was great to see the rocket oven. I recently built something like it with no previous oven experience. A friend had just been in a traditional cob oven workshop (in New York State), and I wanted to build a rocket heater for it. I used an L-feed as time was short and I didn't yet have experience with optimizing a J-tube. I also put an octupus of horizontal flues leading to the edges of the oven floor (no central floor opening). In tests before building the dome, it rockets beautifully and gets quite hot even with random deadfall wood. In our upstate NY fall weather, the dome is still soft after a few weeks... eagerly waiting to dig it out and fire it up with a dome to concentrate the heat. www.facebook.com/photo.php?fbid=10152746349959680&set=gm.10152654431823346&type=1&theaterwww.facebook.com/photo.php?fbid=10203908540327884&set=pcb.10152671281438346&type=1&theaterwww.youtube.com/watch?v=fmcksvqrmeU&feature=youtu.be (the video stops before the fire got hot and started to roar.) Some dimensions: feed about 7" wide x 24" long, riser 6" diameter, five active horizontal flues around 4" x 3" equivalent. The dome is 27" diameter x 16", and will have a chimney over the doorway for draft and fun, sculpted into a dragon similar to the sketch in Kiko Denzer's book. The door is 16" wide x 10" high. |
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Post by Donkey on Oct 30, 2014 19:58:37 GMT -8
I dig the sand out IMMEDIATELY! If you have compressed the dome properly, it will hold no problem; if you have NOT compressed the dome well, it will collapse.
A cob dome with wet sand inside will stay wet for weeks, maybe even months. If you dig out the sand right away you can have fires in the thing in 2 or 3 days.
I usually start small, dig a hole in the door just big enough to get my arm into, dig out the sand by hand. When the sand is out, I will carefully carve the door opening almost to it's final height but keep it on the narrow side. I let it dry overnight or maybe 24 hours depending on conditions before carving the door to it's final dimensions.
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Post by patamos on Oct 30, 2014 20:32:42 GMT -8
If you haven't compressed the dome, you could try putting a little 1500 watt heater on its exterior in places. A lower 700w setting a few inches back and moving it around every few hours will minimize shrink cracking. Will probably take a day or 2 til it is hard enough.
Then there is the old propane tiger torch option... less and less fun the more i do it...
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Post by Donkey on Oct 31, 2014 7:20:45 GMT -8
Chances are pretty good that if the dome is NOT compressed, it may fail anyway.
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Post by patamos on Oct 31, 2014 10:32:00 GMT -8
Ya true.
I am relatively new to rocket stoves/heaters so i would recommend anyone refer to the opinions of much more experienced members of this forum.
There tends to be a trend in development from 'excited newbie' to 'keener novice' to 'seasoned expert'. In a way, the somewhat experienced keener novice who thinks he knows more than he really knows is the most dangerous.
I consider myself in that middle category... My only saving grace being 15 odd years of natural building experience and a few masonry heaters under my belt, which has brought me a sort of intuitive knowledge of many of the materials.
I love this forum. And i am profoundly grateful to Donkey, Matt, Peter, Sata, Kari and others who have piped up to help me learn via open source.
So, with all that said,
Do you think setting some loose weave burlap in a 1/4" skim of plaster on the (current) exterior of an uncompressed dome would help it hold together?
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gjh42
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Post by gjh42 on Oct 31, 2014 16:11:10 GMT -8
I'll check it when I get back in the morning and see how it looks. The doorway (10" deep with a chimney opening in the top) is built of straw cob on a wooden arch form, and was fairly stiff and self-supporting when I looked last week. I believe we compressed the oven mud, though I am not certain exactly what process you mean when you say that. We didn't paddle it, but left the outer surface rough to give a toothy bond with the insulating layer (not on yet). My experience building cob kilns has been in summer months when the temperature is 30-50 degrees warmer than it is now; also, I don't use a sand form, but build any arches on bent withies.
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gjh42
Junior Member
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Post by gjh42 on Nov 1, 2014 19:54:57 GMT -8
The oven mud was pretty soggy when we applied it, wetter than I would have made it; but by this morning, it had stiffened up enough that we felt confident digging out the sand. That came out neatly with a bunch of effort as it was very well packed and had a touch of clay as binder, but it is looking good. I will finish digging and sweeping it out tomorrow and put a fire in it to get it good and dry. www.facebook.com/photo.php?fbid=10204204679851187&set=pcb.10152763710893346&type=1&theater |
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Post by matthewwalker on Nov 1, 2014 21:31:50 GMT -8
That looks really nice Glenn, love the stone work.
Pat, I think the composite approach is really cool, I've been doing quite a bit of that myself lately. In the case of the dome, it might help hold the outer skin together cosmetically, but I think the forces are going the wrong way for it to add much overall strength to a dome. The fibers in a composite give it strength in tension, but in the case of a dome, if it's going to fail, it will be due to compression so the fibers won't save it, in my opinion.
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gjh42
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Post by gjh42 on Nov 2, 2014 9:29:46 GMT -8
Depending on fiber orientation (if the fibers go in all directions rather than a two-dimensional layer), fibers might help even a dome structure. The path of failure in compression for a rigid granular material will be for particles to spread laterally (inward and outward), so fibers that run from inner face to outer face will take some of that force and delay failure. Of course that is not applicable to a layer of burlap in the outer face unless the material is trying to bulge outward.
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Post by matthewwalker on Nov 2, 2014 10:29:41 GMT -8
Right Glenn, I agree. I should have clarified I was speaking not about fibers incorporated into a mix, but rather a lay-up of a sheet over the outer skin. I still there are gains to be made by doing it, it just won't save a dome that was going to collapse anyway.
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