Hi everybody, I was wondering if there has any recent developments regarding a cast J tube?

I have seen the ingenious P channel that can be installed as an after market accessory but are there other things that could be done to inprove the basic design if starting from scratch?

I would like to cast a 6” system, I was wondering if I can get more air control in anyway and I would like to hear any ideas of how to and where to install secondly air.
I am happy to atempt any shape castings as I have the tools and some previous experience.

I have read about the P channel and trip wire but I wonder if a vortex design would be more efficient?

I have in fact already built a rocket stove and it works very well but now I have got the bug and I need at lease another one!
Thanks Fox.

Hi Fox;  Welcome to Permies!

Well, Fox the cast  or built J tubes have about reached their potential, with the peter channel and the trip wire. No longer are folks casting but using ceramic fiber boards instead, to build a core and ceramic fiber blanket to build a riser. They are the newest thing in J tubes.

All the newest experimenting has been with horizontal batch boxes.  Burn time is only marginally extended  with a BB, but the temperatures are noticeably higher !  There is no open flame with a batch box.

By all means experiment with J tubes, innovation and radical free thinking is what developed them in the first place, batch box's came about when j tubes reached a temperature max and the innovators wanted more...  See if you can improve on the J tube design and surprise us all !

Hi Thomas, thanks you, I am happy to go with the flow rather than re invent the wheel... so you say ceramic blanket for the riser?
How does that work?
I am familiar with ceramic fibre board and blankets as I build pizza ovens but the board I have handled is quite soft to resist abrasion in a fire box?
I have seen the batch box designs, they look great but a J tube suits my needs better for the moment anyway.

Here is my present cook stove, it works well and can reach 450 + on the top plate but it takes a couple of hours to really get hot (I think due to the casting mass)

Using the ceramic blanket is called the five minute riser.  That's how long it takes to build one !

To start, I recently discovered that not all CF blanket is created equal.  The cheaper Chinese copy's are very carcinogenic. Same as or worse than fiberglass insulation.  The most readily available safe blanket to buy is "Morgan superwool plus".  Completely safe no hazardous warning label needed.  Of course it costs more...

Here's how it works.  You are wanting to build a 6" rocket.  You will need 8" black stove pipe in the required length for your riser. You will want a piece of   1" thick x 24" wide x 6' long  superwool plus. It is available in 6 lb or 8 lb weight.  6lb has been found to be completely durable.  An appropriate length piece is cut and tightly inserted inside the 8" pipe , a second piece is inserted above to make your required length of riser.  You now have a 6" ID riser that can handle 2300F or more .  The original inventor is still using the very first one over 2 years later ! 

The ceramic boards are not durable enough for use in a feed tube ,  1/2 thickness  split firebrick is being used to form the feed tube and 1" thick CF board is being used for the burn tunnel and start of the riser.

That sounds too easy!
I have a good stock of ceramic blanket, although it is 50mm thick, I am pretty sure the stuff I have is as safe as it gets but I will do some revision.
I actually live on a small island just off the coast of France but I can order most stuff ... at a cost!
Anyway thanks for that, I can quite easily change my present riser and see if it speeds things up.
My riseris made up from four 30mm thick sections so a lot of mass, I don’t think that is a bad thing as it will hold heat for a long time but it is slow to get to temperature?
Is there a thread about useing blanket for the riser?

Well there really isn't a good post about the five minute riser because... its so easy ! Heard that somewhere recently... would be a short post... :)
With 50 mm blanket you would want a ten inch pipe for your 6" riser. Being in France, I'm sure your blanket is the safe variety, I was told that in France/ Europe the hazardous kind is only sold to professionals. Only in the US can john and jane doe readily buy highly hazardous material thru the magic of the internet!
Your riser's look very good as does your stove ! (Dinner looks very good as well !) But I believe you will be impressed with the five minute riser.  No riser mass to heat means more heat going faster to its destination.  The ceramic boards as a core speed that heat along as well.

Here is a link to another RMH group.  http://donkey32.proboards.com/  ; You will find a vast amount of information there as well.

Great, I am excited, I will build a new riser as soon as I can get some 10” pipe.

I do like my stove it is really good fun, I have fitted a rotating plate that can partially cover the exposed end of my chimney.
For the fist hour or so I can adjust the heat by moving the plate to cut down the air flow and it offers quite good control of the burn rate, an important asset when cooking but when my fire has been running for two hours the plate  stays really hot even without a fire.
I think this is because the risers mass holds so much heat, it will be interesting to see what difference a ceramic fibre riser will make.

We have done a lot of cooking on the plate this summer, mostly done with the fire choked back to hold the temp around 220c but I have seen over 500c and a slight red glow from the centre of the hot plate.
At those temps it just destroys food but it does heat the room space.