Where does the arch sit exactly?

[wolvis]

Feeling pretty stupid that I haven't been able to work this out exactly from all the amazing builds on the forum, but it could be early onset senility, or the fact that I haven't yet found a project which exactly matches.
I am trying to ascertain precisely where and how the arch fits into the dome wall. I have studied the online plan, which doesn't show how the bricks are laid. I'll keep looking but if anyone knows of more detailed drawings, I'd be grateful. Mine is a 36" Pompeii with the floor sitting inside the dome wall, not underneath, made of 3" thick fire bricks. I'm currently thinking of having half brick soldiers as the first course, which would leave them standing about 1" above the floor. The cooking floor is pretty much laid, on loose kiln-dried sand with a little fire clay and brick dust added. The insulation is 50mm ceramic fibre board wrapped in aluminium foil to keep the water out. Just need to figure out exactly how and where to turn the corner into the arch and the vent landing.
Archway is going to be a soft "Roman" arch, I hope, (see middle pic) 18 inches across and 12inches at its highest. Thanks to all those, especially JRPizza who have already helped me along the way.

[agrasyuk]

I know how you feel exactly. Had a brain dead moment when it came to actually starting my arch. IMO That line you have on your oven floor marks perfectly where you should have your arch inner side.

Other then that I can only show how I approached it

[JRPizza]

Wolvis, cut a duplicate arch board and make an arch form. Make sure you reduce the height enough that you can put some shims in, or you will have a very hard time removing the form after the bricks are set. Place the form where you think the forward/outward edge of the arch will be (see first pic), then place a full brick at top dead center and make sure you have enough sticking back to intersect the dome (you will need to use your IT or a ruler). In the second pic I am holding a dome brick in my IT to make sure it fits on top of the TDC brick. It's kind of hard to tell but the dark diagonal line on lower left of the brick represents the inside of the oven, which is the rear of the brick in the IT bracket. Ignore the diagonal line on the upper right - it's a goof!

[JRPizza]

PS, I used a rubber type respirator with the replaceable elements and it fit tight against my face with no leakage. When I cut my insulation there was a layer of glass crystals on the table and I ended up wearing quite a bit of it. Your mask may be OK if you are sure there is no leakage around the edges, especially after it gets full of moisture. You really don't want to get any of that in your lungs.

[Gulf]

Great advice. I know this is not a best practice, however I used a regular dust mask. I kept my work down wind and created a little more breeze with an electric fan. But, then again, if f I were as young as some of you folks..................I would probably use a level A hazmat suit .