what you need is a simple wooden template to place your bricks on as you build the internal arch, there's no plan its just what your own specs are, mine is 3 1/3 brick deep, WHY ! because thats the solid brick i gathered so thus thats my design. the 1/3 i think is important, not that its a 1/3 but that its NOT a whole, so I can create my arch like bricklaying where it itersects.
I've chosen to do an arch that is pretty flat, aca less mortar is used. the internal height is mostly acheived from upright bricks as the first layer (uses less mortar) and then 1 brick layer horizontal before the angled brick before the arch bricks.
This is a good way to define your arch, just lay it out on the pavement, you see here I intend to use uprght bricks, then a flat brick then the angle brick beofre the arch , you will also notice I am using a thin brick at the top of the arch, some call it a "keystone" but fo r me its simply that I found these cut bricks and feel that having a thinner brick at the top will create a stronger arch and less mortar. I haven't used my red bricks for this image as I don't want to damage them.You can see I have achieve a good sized height within the oven using the setup shown. I don't think you need excessive height but proportional height to width whilst considering the middle/front drop aspect for smoke escape.
using upright bricks to create height is also better ( in my opinion) then a complete arch from the base up as the vertical walls will also reduce the chance of mortar falling into your food.
(mortar mortar mortar, you can see this is a recuring word, the reason is....for me.... is that because i am doing this on the cheap i need to implement as many techniques as possible to make it function like a "bought one". I did consider doing a clay arch with vermiculite but as i got the solids for free that swayed me, + vermiculite isn't cheap. I will be using clay as an insulating layer later on but it will be mixed with sand and i have some interesting info about that process as well. )
you simply prop the arch template up on loose bricks and once the mortar has set you remove the bricks and the template falls away leaving you with the "tunnell" of bricks which forms the main oven chamber.
any left over mortar can be spread over the outside of the oven which will add strenght.
Once the template is removed we build the back wall and start on the front slops, chimmeny "draw" and the front facade.
Here you see me mapping out the cardboard template that I will then cut the wood form from.
NOTEEEEEE: you may have to do this a few times as i STRONGLY suggest once you have cut the cardboard fold it in half and see if it is lopsided or not BEFORE cutting your wood, i made this mistake ! so you don;t have to LOL.
But you can see here already how nice an arch it will be.
See here how I have marked the bricks placement but also the middle and edges, this will help you later if you use wooden slates, if you use bent board you won't need this.
the other line you see is me marking the placement of the wooden slates i will be using, i just placed the slat up against the brick and marked it, mine are slightly smaller in width to the brick which helps greatly on getting the angle correct.
Having said all that you don't need to make it PERFECT but if you can great.
You will also notice the small gaps in the bricks, this is where and WHY you need as straight an edge brick you can get as I will need to fill that with mortar.
