Finally got around to pulling one off. It ain't too pretty, but dang does it work. This is just the prototype to see if the concept works, and I'm going to work on a newer (and prettier) version when I get some time.


Body is made of 0.005" Ti and pot stand is BPL Ti rods.


Inner Chamber


Scale Shot...37 grams


Fits nicely into the BPL 550 pot.


Pot on stand.


Nice big flame


Pot on Stand with Flame (Flash)


Pot on stand with flame (No Flash)


I threw some water in the pot - maybe 400ml or so - I didn;t time it with a stopwatch, but it was in the 5-6 minute range to full rolling boil. It was getting dark, I was happy with the results, so I called it a night.


The pot stand was last minute to test the body of the stove. I wanted to see how it performed and I really just wanted to see if I could boil some water with this thing. I need to develop a new pot stand, and come up with a better way of sealing off all the crevices. Right now, I have just bent all the corners over - and it does work surprisingly well, but I'd like it to look a lot more professional.

Enjoy!

Edited by Steve_Evans on 07/16/2008 22:49:35 MDT.

Very cool.

As far as pot stand goes..

Almost all of us carry titanium skewer stakes. There has got to be a way to use those as the pot stand. I use them for my alcohol stove and one of my wood stove prototypes i didn't like. If you added holes for 3-4 of them to thread into with a way for them to bottom out and a small hole for the tip to center in you'd be able to save the few grams of a pot stand and multi use some gear.

my 2 cents

way cool. look forward to seeing a finished product.

Nice!

Where did you get the 0.005 titanium? That's very thin. Do you have a sense of the durability you might expect? Does it flex when you put a full pot on it?

The book I found on high efficiency wood stove construction suggests using a windscreen/chimney combination that wraps around the pot (see my recent post with pictures of high efficiency wood stove). I don't think it would add much to the weight because it can be constructed to support the pot, eliminating the thick supports you have.

Edited by herman666 on 07/23/2008 07:30:09 MDT.

nice work Steve. looking forward to the prettier version.

Herman, I think 0.005" Ti is the same material used in TiTri. That will give you a reference to its durability. TiGoat sells 0.005" Ti foil.

What Grade is this Titanium? Grade 1 or 2 or Grade 5?

How often do you have used it yet? Titanium has a beta-transus temperature at which it changes its structure and becomes brittle. Can you notice anything like that? Haven't used Titanium yet because of these concerns.
I hope you can eliminate my concerns ;)

Greetings from Germany
Oliver

Huzefa has got it right - I used the Ti Goat 0.005" titanium. If you handle the Ti sheet on it's own, it will feel very flimsy, but once it has the bends added, and bonded with the other parts, it creates an extremely rigid structure. It does not flex at all when loaded with a pot of water. In fact, I won't have any strength issues with this.

5 minutes passes...

I just did a crush test using my hands..I would say that you would need a good 10 lbs or so before anything went wrong. Like I said before, it's the structure that creates it's strength. Of course, that is with the body alone, the pot stand, made of the Ti wire, is very flimsy. I only used that because I wanted to test the body of the structure and didn't have any plans for a pot stand. I wasn't sure it was going to create the flame pattern seen on the bushbuddy - and it does. I plan on making a proper pot stand/wind shield on my next version.

Snuffaluffagus,
Good point about the Ti becoming brittle. I have boiled a few liters in it and haven't had any issues, however, it hasn't seen anyhthing near severe use so we will have to wait and see. Is a standard wood flame hot enough to chaneg the properties? I'm not sure. What temperature can it handle?

I actaully want to press the bottom and top plates into the shape instead of using the orgami technique in the current design. This will allow the walls to be truly round instead of the octoganal (what the shape of 12 sides?) shape it is now. I just need to finish up a few projects before I get that deep into this one.

At 37 grams, I would be willing to give up a little strength and longevity. My only complaint with the BB is that you can bring esbit tabs for a few days and come out lighter...the Ti version fixes that.

Oh yeah, I'm not sure what grade it is. The thinnest Ti 6AL-4V I have seen is 0.016" thck, and if I used that the weight would be too large and I'm not sure how easy it would be to bend/form.

I do have some 0.016" on order, but those are for my Ti Crampons...coming soon...:)

The lowdown on annealing titanium can be found here:
http://www.key-to-metals.com/Article97.htm
If you look at the temps involved in the table at the bottom, you can see there's not much to worry about at small woodfire temps. In any case, the effect of heating and cooling titanium is generally to make it more ductile, so it shouldn't become more brittle, as long as you let it cool slowly rather than chucking a pan of water on it. Even if you had to do that in an emergency, it wouldn't affect it much, and a subsequent firing would re-anneal it anyway.

However, direct flame for extended periods can be a problem, although I would say a coat of wood tar on the inner surface should sufficiently protect the titanium:

http://www.azom.com/details.asp?ArticleID=1245
"Most titanium grades are typically stress-relieved at about 1000°F (538°C) for 45 minutes and annealed at 1300°F (704°C) for two hours. A slightly higher stress relief temperature [1100°F (593°C), 2 hrs.] and annealing temperature [1450°F (788°C), 4 hrs.] are appropriate for the Grade 5 alloy. Air cooling is generally acceptable.

Although no special furnace equipment or protective atmosphere is required for titanium, a slightly oxidizing atmosphere is recommended to prevent pickup of hydrogen. Direct flame impingement for extended periods, leading to temperatures in excess of 1200°F (649°C), should be avoided because of the potential for contamination and embrittlement."

You could consider a thin throwaway steel liner made from a food can if it becomes a problem...

If you are going to try to roll-form it, a full annealing prior to working it would help. It's not very ductile stuff though, I think it'll be the very devil to create flanges etc on. Your duodeconal form may be the way to go. Alternatively, you could roll and rivet the tubes and joint them with a U section pressed ring.

How do I get my hands on some of this 0.005" sheet Steven? :-)

Edited by tallbloke on 07/24/2008 03:12:21 MDT.

I read ti crampons ............???

walking crampons i suposse?

could you add a pair to my axe ?? :-P

Steve .. you going to be our little budha ;-)

Edited by pitagorin on 07/24/2008 02:57:44 MDT.

per Huzefa S post (above), 0.005 Ti may be had from TiGoat :-)

One last thing. What is the height and diameter of your stove?

"you could roll and rivet the tubes and joint them with a U section pressed ring."

That's the plan. I played around with some of the material and as long as you don't try to draw the material too much, it takes form quite easily. Picture below to get an idea of what I am looking at doing.



Size is O.D. 3.625" x 3.5" hieght...I think.

Steven, do you think you can use 0.001" BPL Ti foil for the inner wall? That would make your stove much lighter. For outer wall it may prove too flimsy I guess.

Also by using thinner inner wall you will probably be able to heat secondary air hotter and much faster.

Huzefa...you're always looking to go lighter :)...good idea. In reality, the outer diamter is the structure which is taking the load from the pot. The inner diameter "hangs" from the top lip. As long as it would be strong enough to hold a handful of twigs - which it will be - we could go with the 0.001" wall. Now, I haven't held the BPL foil so perhaps it isn't up to the challenge. I'd have to test it out to know for sure.
Also, with a wall that thin, we might be more prone to burn through or damage from fire - just a thought...I'm pretty new with the whole titanium thing, so we'll all learn as we move along.
Steve

How do you press the ring?

Steve,
I think the whole design needs scaling up a bit, you'll be lifting the pot off to put more twigs in every 1 1/2 mins at those dims, plus snapping thicker twigs to such a short length becomes a chore.Volume increases exponentially with surface area, so you'll get a better burn with not too much extra weight. I'd go for 5" dia and 5" height.

How about spot welding the ring and walls?

Do Ti Goat sell sheet? I can't find it on their site.

Rog, I think this is the titanium foil they're talking about.

Adam

Rog, I am guessing that Steven was trying to make something thats fits inside his pot.

But yes it is a bit too small. BPL Ti foil come prepunched and is 4" in height. If you can use it as it is without modification it will save you some time and effort plus give you some extra height. You can make it wider and store your pot inside the stove.

(edit) p.s. Steven, did you get my PM?

Edited by huzefa on 07/25/2008 20:14:23 MDT.

Adam, thanks for the linky. How do you embed those in posts? I've tried a href's but it doesn't work for me.

Edited by tallbloke on 07/26/2008 04:29:35 MDT.

Rog, my p.s. was meant for Steven. sorry, forgot to mention that.