John Palombo

Yes, I'm rebuilding the core. If I do what you just suggested, then it will be a 9" pipe, or more, when it all burns out, instead of an 8" pipe. Is that okay?
Thomas Rubino built his whole core out of cement - so it's not doomed?

The piping in the whole system is 8".

Here it is with the barrel in place, just for kicks. You can see how it used to be just packed with cement where it will now be open, once I cut away the barrel. The clay stain pretty much goes all the way to the bottom lip. So this is the basic shape, but much tighter, that I will cut out of the barrel.
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea5.jpg

Right, so I have an 8" system, and kept my bench around 30'. For the bell, I think what you're talking about is the feed and heat riser, so I've had it as an L tube, the feed 7"x7" square, and the ISA of the heat riser is an 8"x35" steel pipe. The pipe is 1/4" solid steel, so I felt it would be fine with resisting the heat.

I just put a second coat of cement (with a lot of fireclay in it) on this transition area - it will be covered with cob to finish, but it's basically ferrocement in these shots. This is quite a bit deeper than it was last winter - more bubbled out now than slanted directly down into the flue.

The transition area top lip ended up kind of high, so my plan is to cut away the barrel right here to match this shape:
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea2.jpg

Here is a better angel that shows more of the over all shape and size of the transition area:
https://dl.dropboxusercontent.com/u/4437344/RocketStoveTransitionArea1.jpg

Once I have the barrel cut to fit just inside the transition lip, I'll cement it over with mostly clay and sand, probably a little Portland, and then pack around it with cob. I think I'm going to shape up the floor of the transition area, where the barrel meats the masonry, with the pearlite/clay mixture. While it's still wet, I'll gently press the barrel into it to indent it. Then I'll complete the insulation for the heat riser, the pearlite/clay mixture contained in 1/4" hardware cloth. I'll keep the top gap around 2"-3" - it does have a removable lid as well - and the side gap around 2" - 2 1/4".

Thanks! I'll see what I can pull off. My bench/flu is about 25-30' long, and my chimney rises a good 8' above the top of the barrel. I don't know what a bell ISA is.

I know it hasn't been burning well. That's why I'm expanding the transition bell, as well as the gap between the insulation wall and the inside of the barrel. The gap at the top, between the top of the riser and the top of the barrel, was also about 2 1/2", and I'm thinking of tightening that up a little too.

The link works fine for me. Here it is in a public album on Facebook, with another close up of the top of the core. You should be able to see them.
https://www.facebook.com/photo.php?fbid=839281396091080&set=a.522737061078850.127598.100000276815947&type=1&relevant_count=1
https://www.facebook.com/photo.php?fbid=839281442757742&set=a.522737061078850.127598.100000276815947&type=1&relevant_count=1

Hmm, well I've been using that steel pipe for 2 winters, and the inside looks pretty tuff still.

I just used a 1/4" thick piece of piping that I got from the local metal yard. It's pretty rockin. It'll get hotter than your concrete will. How big was the gap between your heat riser and the outer barrel?

Thanks!
For #3, you're saying to use the chicken wire, even though you just used a barrel? Doesn't sound like it matters much what i use, and the sheet metal OR the lathe that I already have will work fine.