new micro woodgas stove (lots of pics)

smersh

BANNED
Joined
May 9, 2009
Messages
1,785
I've been reading about the various gasification stove projects here and elsewhere with a lot of interest. I've got a larger wood gasification stove (a commercially produced Woodgas XL, which is about the size of a gallon can), and have been meaning to build a quart can stove of my own. In the back of my mind, though, I've continually thought there has to be a better way to do this....

My goals:

- more compact than a quart can

- lightweight: 8 oz or less

- sturdier than a can stove, without having to fit parts together

- integrated bottom plate, to catch ash

I started keeping an eye out for a suitable vessel to use as the platform. Every time I saw a double-walled stainless thermos, I would look at it and try to imagine it being transformed into a stove. The problem is that they're all too tall, or have too narrow of a top. Poking around, I found a little stainless tumbler online:

http://www.amazon.com/INTERDESIGN-21860-Forma-BRSH-Tumbler/dp/B000UJC6QM/ref=pd_sbs_k_4

31elAbXGvdL._SS500_.jpg


It's made by Interdesign, and the model is the Forma 21860 tumbler. I found one for ten bucks at Target in the bathroom supplies section. It looked promising, but once I got my hands on it, it seemed really heavy (probably 10 ounces or more), which was a double problem -- too heavy to be worth the trouble, and hard to work with.

Then the other day I was at the Container Store, and they had the same tumbler on the shelf. I looked more closely, and realized that there are two slightly different versions of it -- they had both, all mixed up together. They look the same from the outside, but one is half the weight, and clearly made of lighter weight stainless steel. Visually, they're almost impossible to tell apart -- the lighter one has a slightly crisper angle to the top edge, and the bottom inside surface has rippled concentric circles (you can see this in the pics below), while the heavier version has a completely smooth bottom.

Unfortunately, I don't know which version is newer, or more likely to be in stock at retailers.

4.8 ounces, 3-7/8" high, and 3-1/8" at the widest. Score.

The clerk wrapped it carefully in tissue paper, telling me she'd hate for me to get home with a scratched up cup. Heh, heh.

This is a pretty crude homebrew mockup, but I think the design has real merit. I initially thought I would use an Irwin Unibit, which is good for cutting into sheet metal. That tended to skid around too much, and it was a hassle to get inside to work. So instead, I used a 5/32" titanium double-cut bit, which worked pretty well. The pimples around the outside are from popping through with the drill, and bumping the outer wall. A little unsightly, but so it goes. Obviously, this would have worked a lot better with a drill press and a better clamping system. Even so, it turned out ok.

I taped up the sides and top edge to keep from marring the steel too much, and went to town. I just used a small punch to give the drill bit some purchase, and then simply drilled out each spot with a cordless drill:

smershstove2of23.jpg


smershstove3of23.jpg


smershstove4of23.jpg


I did the same thing on the inside, making a number of ventilation holes on the bottom of the combustion chamber:

smershstove6of23.jpg


smershstove7of23.jpg


Then, a cleaning slot so that any ash that gets down through can be poured out:

smershstove9of23.jpg


smershstove10of23.jpg


enlarged with some very crude dremel work:

smershstove11of23.jpg


Add a piece of gutter screen to lift up the fire to get a bit better airflow:

smershstove13of23.jpg


So how did it turn out?
 
Last edited:
Polish the rough hole edges with a little sandpaper, and there you have it:

smershstove12of23.jpg


The Smersh Stove lives!

This thing is little -- with a BRKT Liten Bror for scale:

smershstove14of23.jpg


smershstove15of23.jpg


Gasification:

smershstove16of23.jpg


smershstove20of23.jpg


smershstove21of23.jpg


smershstove22of23.jpg


It works! It clearly is gasifying, and it burns down to a small pile of ash.

The post-mortem:

As a proof of concept, this definitely works. It's a bit trickier than a quart can stove, since the combustion chamber is smaller, and the gap between the inner and outer walls is thinner, making air flow trickier. That makes it especially important to have good dry wood, in very small pieces. Even so, it works fine, and should easily boil up a pot of water very quickly. With some refinement it should make a good solo or daypack stove.

It would probably work well as a chamber for an alcohol stove, too. Worth trying, anyway.

Here's what I think it needs for round two:

- Better airflow at the bottom of the combustion chamber. I think I'll enlarge some of the holes in the bottom, and maybe see if I can drill some additional larger holes directly into the corner of the bottom, at an angle. I'll see how that works, and then maybe enlarge the exterior air intake holes.

If anyone is interested in trying one, please chime in with your results, mods, experiments! All I ask is naming rights.

;- )
 
Last edited:
Great work! That is an excellent experiment; I look foward to some use in the field to see how it works out. Boy, compared to the Liten Bror, that is quite small!:thumbup:

ROCK6
 
I am thoroughly impressed! What was the final weight of the Smersh stove? Have you done a boil time for a given amount of water?
 
No boil times yet -- I still need to rig up a pot stand (either with coat hangers or maybe with wire mesh).

Apparently the holes I drilled didn't appreciably lighten it -- so it still weighs in at 4.8 ounces.

I just enlarged some of the bottom holes and just fired it again. Testing, testing....

;- )
 
Sweet work looks good too ,I can`t wait to hear the boil times. I will make one once you get the bugs worked out .Thanks for doing the legwork for us man!!
 
I have a junk thermos that I'm tempted to do the same to now, from the looks height and width need to be around a certain ratio, or could the same be done with a taller/narrower or shorter/wider setup?
 
Would a round disc of metal (like the cut top of a soup can) dropped on top of the fire once it's burning force it to pull more air through the inner chamber? Nothing too tight, just let it ride the burning twigs down to the bottom.
 
Minor update:

I enlarged the holes at the bottom of the chamber, as well as the intake holes on the outside. I think that helps. I did another burn with a pot stand, but it was really windy and the height was wrong. More dinking today....

Not sure about adding a disc -- I suspect it would cause more hassles than it would fix. Not sure, though.

There's probably an optimal height/width ratio -- I'm not sure what the golden proportion is, but I bet most stoves are a bit taller than they are wide for a reason.
 
Excellent work. That is a beaut! Now go boil some water on the trails and keep giving us updates on how it works out in the wilds. Looks like a perfect backpacking stove and I like how robust it is.
 
Back
Top