The slow and steady progression continues on the first chamber. I finally made it up to the section where the rear arch that springs off of the flue and meets the main arch. It was a bit unnerving at first as I didn't know exactly how it was all supposed to fit together. I'm trying to do it with as little brick cutting or castable as possible since both diamond saw blades and castable cost quite a bit more than the used bricks we have. After wrecking several bricks with cuts that didn't look quite right, I ended up with this.
--a single simple cut on the main arch. I'll still probably end up laying down a small coil of castable to seal on the joint as it isn't all that tight. I think it should be structurally sound though. I've never seen a Bizen kiln in person, which is unfortunate since I'm sure there is a better way of doing this. For those of you who aren't familiar with Bizen kilns there is a nice web page out there of Makoto Hatori's Bizen Kiln. At the bottom of the page you can scroll through the building process. Two things are evident: First bamboo makes a beautiful arch shape, much more natural than the pointy catenary arch. Second, it certainly looks like he built his first chamber without cutting too many bricks or using any castable.
Lots to learn