So...after (too many) false starts the actual build is now in place and really - seriously - commitedly in progress.
I looked at the same stuff over and over and finally a useful pattern emerged...:
This needed to be off the floor=> hence the old cast iron stove base which I'd already leveled with assorted bits & bobs.
The base needed expanding to be usable so on top of that went the funky 7-sided kiln ends.
Stubborn old me wanted both vertical and horizontal access at the 'front' to the burn tube so that got made from some old, thick stovepipes with an elbow for connecting the riser and a hand-made tee for the vertical burn tube opening.
Both entrances can be capped with a standard stovepipe cap too - so I can cap whichever one needs it - or get a 2nd cap to cap both when it is not in use or if it needs to be snuffed out in a hurry for some reason.
True strangeness starts here=>
The stovepipe parts will naturally be of limited life so they are being used as a mold and under the burn tunnel there is a funky slab of cast iron that was one side of the old box stove that I junked for parts.
That slab boosts up the burn tunnel so the horizontal cap works really well and it also serves as the bottom outside of my 'mold'.
Once all this got started serendipity took over and a great guy at a local business gave me a wonderful ring-type 55 gallon barrel & lid - and that lid forms the base where the barrel will sit so I get the dimensions right (it is also slid under the cast iron slab which makes a slight upward angle for the burn tunnel).
Around the perimeter of the barrel lid I cobbled together a funky ring of angled kiln firebricks and 1/2's of regular firebricks with the exit tube embedded between those bricks.
(Thus far I've not had to use a single one of the really good firebricks as all I've used came from the old kiln & some 1/2's that the potter gave me so I've not even cut a single brick yet.)
This is all placed so as to create as large an exit path as I could arrange and there will be at least 2 courses of firebricks all globbed together with mortar for strength & sealing.
The easiest way I could imagine to form the burn tunnel's thickness was by making a starting layer of mortar + perlite mix - that was done & allowed to set overnight.
Next the rocket tube was made by cutting an opening to form around the 6" burn tube and mating tightly at the bottom and with the bricks so as to keep the perlite in as well as possible; it was then filled between the 6" & 8" pipes with perlite, but not finished at the top because there will be a needed height adjustment for the proper clearance to the barrel end.
Comment about this process=>
Making an insulated pipe with perlite is really quite fun & I highly recommend it !!!
Then I added one side + top of the burn tunnel's body using a board for a form secured by screws & string while I filled it in by hand with mortar for the thicker outer, strong layer to hold it all together.
One thing I am very glad of is that I remembered that when folks didn't have lots of fancy stuff to form things with - they just cobbled them together using what they had to hand with a good mason's trowel - and mortar formed this way, good & wet gets very solid & strong after it sets - and that is what I am doing here.
Yes - I do have some pictures already - but just typing this out is all I'm good for tonight and if all goes well I'll post a bunch after the next phase of building is setting.
Tomorrow, when there is daylight I'll snap some more shots of it's interim state before I move the form board to make the other side/top part - I also plan to add the 2nd course of the 'ring' part.
I will try to get shots before/after each phase to share with the good folks here.
My only wee concern is that I may have made the burn tunnel too long - and once it is cast in, well=> that, as they say is that.
On the flip side of that possible boo-boo though there will be a very big & free-flowing space at the other end so I ain't worrying too much about it becoming a problem, really.
Also I am adhering to my firm belief that this needn't be overly scientific to be quite good & usable.
I got really 'burned out' with all the hoity-toity technicalities I saw cited over at other places - so I am following Kevin Bacon's suggestions that these things can be cobbled together very simply without being too fussy about all of it.
My goals also remain unchanged - I want it to be safe - to make heat where heat is needed - use little fuel - and in the best of all worlds have a really nice, low outlet temperature.
And finally - after it is all made, set & well tested I may also jacket the burn tunnel with some metal that I have.
I am also considering using those really good firebricks as a non-fastened thermal mass along the wet wall beside the new heater - but this is all yet to be determined as trials & observations are made.
All this still depends upon what sort of outlet temp it ends up making - if it is cool enough I still plan to use the flex tubing but if it needs more heat to go away before that I'll bite the bullet and buy some more stovepipe stuff.
This design has allowed me to use up all the goodies I had on hand which pleases me greatly.
So far all I've bought this week are an elbow, a cap and a 2nd bag of mortar.
This critter will have built-in mass aplenty once I'm done swaddling it in mortar and stuff...
It must already (easily) weigh 300 pounds or more between the full (60#) bag of mortar, bricks & cast iron parts - and no matter what I'll also shoe-horn in at least the 2nd (80#) bag of mortar - and that barrel ain't light either.
I'll be getting impatient waiting to see how this will work while it all sets, that's for sure.
Best Wishes to All !!!