Jon Terry

Sorry about that! I've been struggling for hours to get the pics in order with no success and much frustration. Here's a working link, hope you can make sense of the build, each picture illustrates a specific point, but you might miss it when the order is jumbled...
grrrrrrr!!!
https://photos.app.goo.gl/9BoLYo5aUJJAYG4X8

Howdy!
I went over and over my Sketchup plans, made a few changes I won't bother updating here in lieu of sharing a link to some pics of the actual build so far. (Google rearranged their order, I can't correct it, sorry if they're confusing) https://photos.app.goo.gl/9BoLYo5aUJJAYG4X8
Haven't started on the burn tunnel assembly yet, will start that this week. Have a look and tell me what you think of it so far. I'm very pleased with how it came out. It may look perfectly square, but it spread a bit in the middle after filling it with the clay/rock/sand mix, in retrospect I should have welded a bar across the middle on the top to keep it from spreading. Because it spread like that, I had to match the welded top to it to match it so it still looks square. That took a lot of unnecessary effort that could have been saved with a stabilizing bar welded across the top...oh well! Let me know if you have any questions!  https://photos.app.goo.gl/9BoLYo5aUJJAYG4X8

I forgot to mention that lowering the ceiling of the bell chamber resulted in 7" - 8.5" of mass above, up from 4.5 and 6.

Excellent, yes, those were my concerns and feelings there, too.
I tend to go overboard, thanks for pulling me back in.
Here are some more pics, I lowered the chamber ceiling and added another, shortened, pillar.
I've altered the elbow on the pipe leading out of the chamber so it draws from close to the floor, not sure if that's clear from the pics.

Thanks for getting back to me so quickly!
Unfortunately, I have a window sill that limits how high I can go and I'm at the limit now.
If that's the case, then I'd better lower the chamber height back down a couple inches and add another pillar...
Any thoughts on the steel vs cob question?
Much appreciated!

OK! thanks for clearing that up, according to the calculations, each pillar being either 2.7 or 3.4 sq ft, I only need 5 of the taller ones or six of the shorter ones to bring me up to 57 sq ft.
Do you think having only 4.5"- 6" of mass on top of the chamber is too little?
And I'm still wondering about the steel panels. Current thinking on that is I can stack up a couple inches of them and top that off with the cob mix...but I really do love the idea of using more of them to recycle, and I could bring those right up to the top of the mass and leave off the top layer of hardie board I'd planned to top the mass off with. But then I wonder if it'll get too hot...
(There's a steel frame that sits on the mass that allows for an air gap between the mass and the platform above)

Hello, thanks you for your reply. It's an 8" J-Tube.
According to Glen: "Peter van den Berg's batch rocket sizing calls for a 6" batch box to have about 57 square feet of internal bell surface (an 8" J-tube seems to have similar capacity as a 6" batch box). I would estimate that you have around 40 square feet of internal bell surface (the floor doesn't count). Pillars would help."
I wasn't sure about calculating surface area on my pillars, I was also told to add as many pillars as I could without restricting air flow, and I wasn't sure if the two suggestions were at odds with one another.
I'm also worried that I raised the internal height of the bell chamber too much, as Glenn said: "Keeping the mass about 8" thick is probably a good balance between storage and radiation"
It's now 6" at the thickest point and 4.5" at the thinnest, depending on which rib of the corrugation it's measured from.
Should I lower it back down?
Glenn Herbert? You still around?

Hi everybody, I made some changes to the bell chamber as per suggested here. I raised the ceiling of the chamber a couple inches, it's now 4.5" to 6" from the corrugations to the top of the mass storage area. So, I've gained height in the chamber to trap hot gasses, but I've lost a bit in heat storage in the mass on top in the exchange.
I've also added some brick pillars to the inside of the chambers, I was able to poke a layer of bricks up into the raised corrugation.
Did I go too far with all those pillars? I packed as many as possible in there in order to make up for the loss of mass above, I'd be happy to remove some if you guys think it's too many.
Another question I have is- I have dozens of corrugated steel panels, they're 1/8" thick and heavy. I could stack those right up to the top of the mass storage area, even leave them exposed rather than covering them with sand/clay/rock.
Would there be any concerns doing that? In your opinion, is there much difference in mass or heat storage capacity? Will the steel release the heat faster? I worry that it might get hotter than the clay/sand/rock cob. Should I maybe not stack them so high and cover them up with a layer of cob?
I really like the idea of being able to reuse the steel panels this way, even though it means burning all that paint off them first.
Once again, many thanks for your attention and input! Hope you can make sense out of the pics.

oh, I didn't plan on having any sort of screen or barrier on the sides other than the hardie board that helps contain the cob mass, so it will radiate from the sides as you mentioned.

OK then, I didn't see your call to calculate the mass of the pillars until after I'd drawn it up on Sketchup, did I overdo it with the pillars?
I think I do want to mortar them, at least with clay and sand, because of earthquake risk, if they tumble inside there it would be very difficult to straighten them out.
I have plenty of those steel panels leftover from the house, I could throw a few more on top of those, they don't sit perfetly flush on top of one another, there would be a small air gap between them. I guess I need to burn the paint off them first...