soup can cobble job

[dave]

This was my first trial at a rocket stove, made from soup cans held together with sheet metal/screws and JB weld, originally insulated with fiberglass insulation.

Lessons learned. Fiberglass insulation catches fire MUCH easier than one would think. JB weld disintigrates from the heat. A poorly insulated stove still works somewhat.

The first firing with insulation had flames shooting out the top and a noticeable rocket sound going. After putting out the fire and removing the burnt insulation, it was re-lit. The fire was not as aggressive and a bit tempermental, but burned hot. When the fire feeding was ideal, there was only a heat wave from the chimney, no smoke. However, not much of a draft going on.

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PS How the @$%^ do you post pics? I have searched for pictures, pics, attach, etc and cannot find anything.

[Donkey]

There are two methods that I know of.
The one that I use most often is to place my images on the web server that my personal website (said website hasn't been updated for a VERY long time) is on. If you don't have your own web server yet, there are tons of free ones out on the net, for web pages, images, etc. Then link to the image using the img tags.

The other way is to use the attachment function in the reply window on the boards. You gotta make sure that the image is small-ish.. (you need to do this anyway) The attachment function calls up a drive browser, just locate the image on your computer and click the appropriate button. It (should) upload the image to proboards (here) and place it in your post.

That should do it.

[hpmer]

Yeah, the info panel on the fiberglass clearly says it is not rated for the high temps we get in these stoves. "Great Stuff" spray insulation has the same problem (and smells aweful when it burns).

Look instead for perlite or vermiculite to use as insulation.

Also, rather than screws I used a crimping tool to join the cans I use. Works great, creates a pretty tight seal, and no need for screws.

[hpmer]

Try larger cans as well. Pineapple juice comes in 4" diameter cans which is the size I started out with. I've now moved up to 6" cans. The 4" can fit inside the 6" and allow for 1" of insulation all around. Not as much as I like to use, but seems to work nonetheless.

[dave]

Ok will try the pic thing again through an image host.

[yesimag]

nice pic man.

[johnf]

I did something similar, smaller. Cut cans apart and hammered as flat as possible, made a 1.5"sq elbow, about 4" tall. Put it inside a 4"can with fiberglass.
Didn't use any fasteners, except "Insert tab A into slot B". Soon adapted extra "fasteners" of little rectangles of metal, cut & bent into "staples" on the same sale as the tab/slot. Worked fine, except you've got to be careful to not let the slots become permanent open gaps as you bend & hammer them flat (design must include means of sticking something like a chisel or nail extension of some kind in to tight spots to hammer these staples into a tight fit).


Didn't get the fiberglass to catch fire (maybe not enough airflow through it) but it out-gassed tremendously as the plastic/pink burned off, leaving white fiber fluff at least .75" out from the center tube.
Little thing drew and fired just fine! Up to 6" tall strong flame, tiny rocket sound, very little ash for firing it for half hour continuous.

Don't know how much difference any insulation makes on this scale, unless you put a lot bigger body around even this tiny draft tunnel. The entire thing got very hot, so no question about long-term holding any heat in the combustion area.
Body was almost hot enough to light a cigarette, outside of the 2" feed/intake chute easily charred/ignited wood.
Perhaps the design premise must include the fact that the entire thing will get hot, so that's how you keep the combustion chimney hot to burn the gasses, rather than trying to insulate it!

It soon became impossible to keep the fire from creeping out into the feed shelf, even if it then drafted in/up through the elbow! The brick I set it on soon became more than hot enough to be an excellent camping bed warmer...

Basic design premise for a rocket stove on this small scale (up to coffee-can body) : A wood fire this small will get hot enough to ignite wood at least 4" away. You must design with this in mind. Continuous-feed fuel stocks will all go up.

Next iteration will have a slanted fuel feed chute to drop chunks in. Can't use any form of self-feed, since it'd catch fire all up the fuel magazine. (also better material for the inner chimney. Can sheet metal won't hold up for long.)
Quandary: Should I just use this as the air inlet, from above the fire, drawing down? How to direct air under the fuel? Use wire grid to bounce fuel up onto the grate, while allowing air to preferentially go down under the grate/combustion zone?

It'll obviously require continuous feeding, but it'll be great for making tea, ramen noodles, heating a tent/room/RV.

Want to make a hybrid stove on this scale.
see this first
Rocket stove, 5 gallon bucket

www.youtube.com/watch?v=9M-4aUqa7RU&feature=player_embedded

So first, the hot plate (something that can take that heat -was suggested that I use an old cast iron pan, cut down to fit...)
Then run the flue up through a heat exchanger like a ziz-zag pipe diversion or another can for radiating area, before it goes out.

Coffee-can size, no bigger than 2" elbow.

[Donkey]

Aprovecho cook stoves don't use the down feeder elbow.
My feeling is that with little cook stoves, since you are always fiddling with the wood anyway, you loose the advantage of the down-feed, so why have it?

Horizontal feeding does a few things for you. Total control over cook temperature, moving the sticks in and out makes for temp control and easy metering of how much wood gets used. The parts of the wood that are NOT burning are kept further from the extra heat and are less likely to give you the kinds of trouble you've been getting. Place a divider in the feed about 1/3 from the top, build your fire and place the wood on the top of the divider, air will be drawn under the fire and preheated in the lower portion. It's gonna simplify building 'em too.

[johnf]

Good points. Thanks.

I was thinking of the drop-in fuel feed, to eliminate any problem with fuel sticks outside the burn zone catching fire. I used a short horizontal, so I'll try a longer horizontal feed tube, before I hassle with the chute idea.
Make the feed chute long, a tunnel that only will draw inward to feed the updraft. I'll have to see if it won't turn into the sort of thing the mass heaters have: the horizontal burn tunnel (this time with sticks), and the vertical updraft chimney to complete the combustion.

About the insulation: I'll get perlite, but it'll also mean that techniques & tolerances in construction will have to prevent it from falling out everywhere.
As I said, I didn't have an insulation fire, but even so, if the pink fiber is packed in and covered by structure, it will outgas a lot, so care must be taken in using it outdoors, and not breathing in the burning plastic.

I'll play around, and try to get some pics this time.

In addition to a small scale stove for a tent or single room (shop heater), I want something to replace my Sierra Zip Stove & batteries & flimsy tipsy structure (also an uptake chimney to vent it outside a camp tent)


BTW, I like the small scale hybrid "Pocket Rocket" from coffee cans & such.

[Donkey]

Insulation:
If you mix the pearlite with a little clay slip, it will stick together and you won't need to build it quite so tightly.
If you have clay rich soil, you won't need to buy the bagged stuff.