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Rocket stove - hot plate.  RSS feed

 
gardener
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Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Sorry mate, that looks very weird to me.

What is the back, some kind of Koa? Amazaque? Lemonwood?  are your sides veneered endgrain, over a sort of ply form, or pure endgrain cut in the mass?

I was more into huge jumbos myself.



Or classical,



Now, i am more into this kind of things!





 
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Ha ha don’t be sorry, most of my designs and work in general, is of an unusual design, that is what sells my work.
It has a carbon fibre core, the sides are made in a mold that compress carbon fibre onto individual end grain squares (magnolia) the back is made in a similar way but uses quater sawn mahogany pieces.
The neck has a one piece carbon rod that runs right back to the tailpiece.
The top is a carved arch.
This was a commission but I had a free hand to produce something unusual that will stand out on stage.

Your guitars look superb but I could not find a market to sell traditional designs in such a competitive area.
I love working with wood and composites, wether it is a house or a musical instrument but there is a lot more money in houses than guitars!
I have just finished this wood oven with a fibreglass outer finish.
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Fox James
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Well I have some issues!
I built my fire box useing these dimensions 6”x6” square = feed chamber is 8”deep burn tunnel 16”long heat riser 32” high.
What I have found is the heat riser works much better with an further 6” extension, in fact when I load the fire I get smoke out of the heat riser top, not huge amounts but definitely some. When I place an extension on top, everything livens up with more draw and no smoke.

If I have to extend the heatriser that will involve a complete rebuild as to cater for the extra 6” I will need to bury the fire box, dig out my concrete base etc....
I just wondered if there is another method?

I also wonder how effective my heat riser actually is? It is made from one inch thick refactor surrounded with ceramic blanket but perhaps it would work better with insulated refactory?
 
Satamax Antone
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Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Do you have a P channel?

Use bigger wood!
 
Fox James
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No P channel but I did more testing last night, there is such a dramatic difference with a six inch extension that I have bit the bullet and dug out the concrete base!
Hopefully I will get much of it back in position tomorrow......
 
Fox James
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I was wondering about the gap between the riser top and the underneath of the hot plate, I have seen the formulas  but I think they are based on mass heaters.
I guess the closer the better as long as the stove is rocketing well?
I have got hold of a new barrel but I need to burn off the paint before I can test out the new version....
 
Satamax Antone
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Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Fox James
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Fox James
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I have managed a little more progress, I am not sure if it is working at its best?
Nothing is really sealed in place as yet so I have some air gaps around the chimney base and around the hot plate.
After 15mins of burning I am getting 210c in the centre of the plate, no smoke and an ok draw, however if I lift the plate up 25mm ( which stopes the chimney working and I get ash in the room) I then get a much more of a rocket effect and 260c on the plate?
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Satamax Antone
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Location: Southern alps, on the French side of the french /italian border 5000ft high Southern alpine climate.
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Daft me, i didn't think of telling you about this

https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures

How's your transition area between barrel and chimney?
 
Fox James
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Thanks for the link, I had not seen that thread!
I made a 8” hole in the barrel that goes into a small chamber about 10 x 10” so I hope that is sufficient?
I will seal in the chimney to night but I am working on a solution to seal the hotplate.....
 
Satamax Antone
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What's your barrel gap? 

Barrel gap by 8 inch hole surface area. Should be equal to at the very least 1.5 times CSA, better at 3X .

You have a 6 inch heat riser, so that's 28,27sqin.

You need at least  42.41sqin of ring projection in the barrel gap, and the same for the hole surface.

8 inch, you're just a smidge over that. at 50.26sqin

A 8 inch hole has 25 inches of circumference. So, best practice would be to have at least a 2 inch barrel gap. if the gases can access the hole from all sides. Which is rarely the case.

HTH.

Max.







 
Fox James
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I will have a go at enlarging the hole, it won’t be easy .....
 
Fox James
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I managed to get a mini grinder down inside the barrel and enlarged the transfer opening to 9x10 ish.
The gap between the heat riser and the hotplate is 3.5” but I can adapt that if necessary.....
I have done a bit of plastering as well, so I won’t light it until tomorrow.
 
Satamax Antone
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When i say barrel gap, it's the one between barrel and heat riser on the side. On top of the heat riser, most of the guys who hang round here say top gap.
 
Fox James
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Ok thanks, I think my barrel is 23” and my heat riser 12”.
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Satamax Antone
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Ok, you should have said before! I wouldn't have made a fool of myself, explaining the barrel gap then! ;D

So, if, with the enlargement it doesn't work well, the next step would be to insulate the chimney.

Do you have any means to measure chimney stack gases? Sometimes, when you shed too much heat, the chimney kind of stalls. This shouldn't be the case there. But you never know before real life measurement. Anything bellow 60C° and this could be your problem.
 
Fox James
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What do I need to measure the gasses?
I do  appreciate your help and input.
I will be firing it up later today but it is 30c outside at the moment!
 
Satamax Antone
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Yep, measure the gases bellow the first elbow of your chimney. That would be a good spot. If you want to measure the outside of chimney temp, instead, you can, but since it's in close contact with the barrel, i'm not sure the measurement would be very precise. Tho, anything above 60C°, you should be all right.
 
Fox James
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I lit it up for around 30mins but I had to get out of the party house due to it have a clear plastic roof and being 30c outside!
The centre of the hotplate reached 290c ... I was hoping for more, perhaps it will get hotter with more time?
I should of taken a video when it was running fully loaded but I forgot....

 
Satamax Antone
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Sounds quite healthy to me!

Insulate your chimney for more draft may be.
 
Fox James
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Yes it seems to be rocketing away, I am going to try with a thin barrel top above the flame tomorrow, see how hot that gets.
 
Fox James
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I am still not getting the plate temperature I was hoping  for!
I have managed to record 290c on the hot plate, I was hoping for at least 300 so it is not far off but I had to really feed the fire to get that and a more average temperature would be 260c.
The tip of the chimney is around 120c, the draw seems very good, in fact I am surprised at how much wood it can use!
I don’t see any smoke coming out anywhere, if I take the hotplate off, I can see ash shooting up about 12” above the heat riser but no smoke.
The very base of the fire box measures 520c so it s well insulated, I must be loosing heat up the riser?
I wonder if the 1” thick heat riser is to dense?
I have thought about insulating the top 12” of the barrel to perhaps get more heat into the plate?
 
Satamax Antone
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Yep, insulating the barrel could do. If it doesn't stall the rocketing.

IIRC, you said you have 3.5 inch top gap. If you have a piece of metal to make a ring of the size of the outside of the heat riser, make a ring of that diameter, more or less, and 1.5 inch in height. That you could put atop of the heat riser, to reduce the top gap.

There is another trick, making fins under the hot plate, to extract more heat.

And, the question, why do you want 300C° ? Pizza?
 
Fox James
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I also wonder if I could try restricting the chimney exit to slow down the air flow?
Ha Ha not pizza, I can get 500c in my pizza oven, although it takes an hour or so.
I would like at least 300c in the centre to sear steaks, cook lobster, stir fry and whatever likes fast cooking.
I will try out raising the heat riser......
Have you seen any of potty,s videos... he gets 450c on his rocket stove!
 
Satamax Antone
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I haven't seen potty's vidéos.

Well, 300 seems an awfull lot. On my little garden hot plate, i would rather tame the fire. It Burns saussages faster than i would like.
 
Fox James
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He has lots of videos, funny accent but very detailed information back up with real life results.
Feeding pre heated air, secondary air, vortex and adjustable air flow, all seem to be key areas for his own success.
[youtube][/youtube]
 
Satamax Antone
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Well, actually, i have seen this one. I know his work.

But he's a mad experimenter.  And doesn't have his thingies tested by a testo. So, claiming a lot. Amongst all his experiments, which is good or bad, hard to tell.

Hey, what's wrong with his accent?
 
Fox James
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I think this vid shows just how well his fire works ... https://m.youtube.com/watch?v=Un84EZ7XpFg#fauxfullscreen I might have to build a mark two....

I can’t seem to get above 300 and I am burning loads of wood, so I think my design is not really working to my satisfaction but I am not one to give in or compromise.  
 
Satamax Antone
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You want to get a hotter plate.

Have you tried the trick of raising the riser?

Another one i would try, is to put some superwool or rockwool between your hotplate and the supporting plate. That supporting plate is shedding too much heat i think.
 
Fox James
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Yes I raised the riser, went from 290 to 300, averaging around 280 most of the time.
Next up is to try the insulation.
I think you are right about the big plate wicking away the temperature but I often feed 20+ people so I need that outside area to keep food warm while I concentrate the actual cooking above the riser.
Honestly we are having a heat wave at the moment, we’ll for the last three weeks in fact, only 28c today but still 22 c at night and it is no fun working around the stove!
I had a thought the other day, I recon with the plate removed, I could use the heat above the riser to bend guitar sides...... probably  bend a bit of 2x1 actually!
 
Satamax Antone
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Well, i'd rather use a bending iron! :D
 
Fox James
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I have made a modification to the top of the barrel.
I have used some crushed vermiculite and added stainless needles into a bag of refactory so the mix will be more insulating than dense.
Anyway the heat should be able to reach all the hotplate....
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Fox James
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I have just come in from lighting my fist fire in the dark, well fading light really but it put a different perspective on the stove!
I couldn’t push the fire due to the fresh cement but I could see the fire box glowing cherry red, I took the top off and I could also see the bottom of the riser glowing red!
That was after only a few minutes.....so I guess it is working pretty well.
 
Satamax Antone
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Is it due to the photo, or your top gap is huge?
 
Fox James
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The riser is made from four sections, I took off the top two to be able to work inside the barrel.
I have settled on a 2.5” top gap.
 
Satamax Antone
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OK. It seemed big.
 
Fox James
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All put back together, I lit her up for 30 mins full burn. Measured 320c on the center on the hot plate but I put a crack in my new cement top ring thing!
I am not surprised due to my lack of patience, it is a single hairline crack so not really an issue at the moment.
I think the stove is now serviceable but I am wondering about how to pre heat the air for a future improvement.....
I have a few folk coming around tomorrow evening so we will give it a steak blessing...
 
Satamax Antone
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't say earlier, but it's normal that it cracks. Heat expansion of metal is faster and may be greater than concrete. So the barrel most certainly has pushed the concrete.
 
Fox James
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Well tomorrow everning  looks like it is turning into a jamming party with more people than planed so I thought I better try out the hot plate tonight.
Worked very well although it does seem to eat a lot of wood.

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