Lightweight stove for a small mountain hut

[martyn]

Personally i would surround the pieces with 25mm ceramic board and wire them together but if you dont think it is necessary to Insulate then you could try the method i use to fix my pizza oven castings together before insulating them.
Or just wrap some wire around with small pieces of ceramic fibre on the corners.
If the photo loads! ... you should be able to see the stainless steel staples i use
imgur.com/CbaMHkT

[fuegos]

Thinking about the different expansion rates of metal and the casting the staples the Martyn has shown make a lot of sense.The small mass means that you haven't got a big metal band that would take a lot longer to heat up & the fixing is very local , so to speak.Maybe wiring the whole thing together would work for this reason ? a great build for a first attempt , you seem to have a really good understanding of what's needed.Check out Matt Walkers stove chat on YouTube and maybe send in question?

[bombadyl]

Thank you all for the advice.

I like the idea of the wire !

I will probably start without side insulation and add some later if needed.

Nice pizza oven Martin ! I suppose you drilled the concrete before inserting the staples ? I would not dare using a hammer drill on my (precious ) castings... But yours seem way thicker !

Actually now that the base is flat, the 2 halves are almost holding themselves parallel to each other, and you need to apply a significant force to make them move because of their own weight.

Now I have added the vermiculite board on top, and cut it to the correct dimensions. The good side of it : it is very easy to cut with a handsaw for wood ! The bad side : after only 2 cuts on vermiculite, the handsaw will not cut wood anymore . It seems to be too abrasive for my poor saw !

I have used a 40mm wide wood piece to simulate the future Cobra.

And a 150mm steel tube for the riser (which will be later reduced to 100mm internal diameter with 25mm ceramic wool inside and outside).

I have bonded a 2mm thick ceramic fiber at the joint to have the good spacing and prevent air leaks (the ash would have done fine for the bottom part, but probably not for the vertical joint).

Before I read your message Martin I made a small U shape part with 2 flat angle steel brackets, riveted to a straight band. It is just holding the 2 halves with the good spacing but not applying pressure. When getting hot it will probably loosen even more.

I will try adding wire in other locations with protections in the corners.

And on this rainy day I started the very first fire !

Just a firelighter to begin. Then very very slowly adding a bit more fuel (I did not let the fake cobra burn entirely).

Very quickly, the flames were almost horizontal as if they were sucked by the port. That is encouraging for the future !

Not a clean burn yet but it should come later with higher temperatures ,secondary air (Cobra) and less primary air (door).

I did not see water vapor going out of the cast but perhaps it was not hot enough.

When touching the outside faces, the hottest part was near the bottom, just in front of the flames (who would have believed it ? ).

Tomorrow I will try a slightly bigger fire.

I am really having fun with this project 

[pigbuttons]

Truly amazing. Great work and great pictures. I like the bracket you made and I think if you had three more, one more on top, and one at the back around the riser bump out, and another at the front below the cobra channel feature, combined with the clever use of insulation as a gap sealer that you did, and you are golden.

The first couple of fires typically are not enough to drive steam out of the refractory, they are just to start the stress relief process and a tiny bit of curing. And with your style of box I'm not sure you will see steam or not. Just use caution not to go too big too soon.

If you insulate the inside of the riser with ceramic wool, I don't see the need for any on the outside of the riser. The riser will be inside the barrel/bell, right? It won't hurt anything, but I'm not sure it will provide any benefit.

I'm very happy for you and what you've been able to do so far. Thanks for keeping us updated.

.

[bombadyl]

It has been a long time since my last post.

I did not have much free time lately but still managed to make some steps forward.

I made my first steps with arc welding and I still have a huge margin for improvment !
My cobra is not a piece of art but it will probably work just fine.

I made it out of 2 and 3mm thick 304 stainless steel hoping it will last longer than standard steel.

 

I have also made the 5min riser and used the remaining superwool to add some insulation around the firebox and hold everything with steel wire

I also went to my mountain hut and brought a few Kg of refractory mortar to create a flat base ready to receive the stove.

Next step is to create a simple door with a steel frame and ceramic glass.

I will continue to keep you posted as I progress.

[fuegos]

mate thats a great first effort with the welding ! This build is awesome , looking forward to seeing more.

[bombadyl]

New step forward : making a door !

I have used a 1m long L-shape 30x30x3mm profile made of 304L stainless steel and my new skills in arc welding .

Primary air will come from the very bottom, just above the Cobra inlet.
It is not a rectangle but the cross section is computed as per the spreadsheet.

The door has a recrangular ceramic glass as large as possible (I was happily surprised about the price : 10€ shipment in 2 days included).

To hold the glass, I have welded 4 small pieces from previous cuts at the back and added one M3 threaded hole in each.

I have used 2mm thick flat joint between the frame and the glass. Same between the frame and the batchbox.

Then there are 2 vertical strips of 1mm thick steel that prevent the glass from moving and can be dismounted to clean or replace the glass.

Here is the result once mounted on the batchbox.

It will open from the top and rotate around 2 screws at the bottom

[fuegos]

Wow ! is this build of the season ? keep going mate

[pigbuttons]

Everything is looking really good, so cool.

One thing about the glass in the door. It needs to be able to grow and shrink freely, so don't tighten down the bolts too much. If you want to avoid leaks use braided firebox insulation available wherever fireplace inserts are sold.

[bombadyl]

Thanks for the encouragement and advice !

I will keep the back screws as loose as possible.

For the leaks I have already used braided firebox insulation but in a flat version because I needed to keep the thickness as low as possible.

These are the black strips you can see on previous pictures.

I have added a cover at the bottom to increase the WAF (wife acceptance factor) as much as possible

[lsch]

Hi,
I also think that you have done a wonderful thing.
2 remarks though:
-have you planned something to close the air inlet?
-I'm a bit worried about your glass door, when you're going to load your stove, if it doesn't open all the way (to come vertically), it greatly increases the risk of breaking the glass (a piece of wood falling out).
From what I can see, your fireplace has to be high enough to allow for this maximum opening, but even so, it will not be able to swing open completely.

Translated with www.DeepL.com/Translator (free version)

[bombadyl]

Thanks !

No I have nothing planned yet to close air inlets. Do you confirm the need to close them is only when the stove is not used, to avoid fresh air (and ashes) getting into the house ? You never close them during the burn correct ?

For the opening you are right as well. It will not open much more than 100° because the firebox will be close to the floor.
So I guess I will need to be careful when loading. But in case the glass is broken, it can be easily dismounted and replaced for 10€.

[martyn]

Great work so far, you certainly got a good deal with the ceramic glass, that would cost me £30 where I live.

[lsch]

it's a pity, you would have sent the drawing of your door project, we could have warned you of the potential problem.
I confirm, it is necessary to close the air inlet when you stop the stove (when you go to sleep for example) to keep the heat, otherwise, the natural draft will cool the stove and the house ... (no problem of ashes)

[bombadyl]

I understand.
I think it is not too late, I can still add a rectangle of sheet metal to block air inlets and fix it with tiny hinges or something else to the larger sheet metal used as a cover.