36" in Provo, UT, USA

[UtahBeehiver]

You really cannot set a specific length depth, the TDC is the longest brick and defined by the IT. Each brick either side of the TDC changes as you move down the arch so you CANNOT cut all the arch brick the same. They are not linear cuts but skewed. Look the the pic I sent a couple post ago of a hemi or axed arch from Mr. Chipster build and you can see that each brick changes. That is why a full 9" brick to start out with is important. Build your arch form, then place the TDC and mark the angles with your IT. Then looking from the inside out and right side of the TDC brick (after it is cut) becomes the pattern for the left side of the next brick right of the TDC, then use the IT to mark the right side of the same brick. Repeat the process to the end of the right side of the arch then you do the same thing on the left side of the TDC. Again, the arch bricks change as you move down the arch. This is a very tough concept to mentally visualize but once you see it in person the light bulb goes off.

[paulkjrobbins]

I ended up cutting the tabs off so that I could use it to figure out my inner arch length. It is 2" wide now. I can always cut it down again with my angle grinder if needed. Thanks for the tip. I am going to try 5" for my inner arch depth. It looks like that will work. Not sure if there is a benefit to it being shorter or longer but others seem to be around that size.

[UtahBeehiver]

Plus one on JR's comment on the width of the "L" bracket. I even did on about an inch wide for the top courses.

[JRPizza]

... I have a welder, it doesn't mean I am a welder.

That's funny and describes my level of welding talent too You might want to make a thinner/reduced brick holder for those courses up near the top when the bricks get smaller.

[paulkjrobbins]

Here are some close-ups of my IT. It is not pretty but it works. Tried to make it without a trip to the store, ended up having to get a threaded rod. As you can see, I have a welder, it doesn't mean I am a welder.

[paulkjrobbins]

I have benefited so much from advice as I've gotten started I figured its time I post some photos. I started out planning and building a 42" pompei but later decided to do a 36". This was after I had already puored the foundation, walls, hearth slab, vermicrete, and cutout FB. As a result, my oven is on a large slab with room to spare for a little counterspace. I am doing 4 1/2" firebrick floor on 2" FB & 7" 5/1 vermicrete. Here are some pics of where I am right now. I used my straight edge to check for level. The center ended up being right at the edge of a brick so I decided to do an "L" insert for my IT. It is set high right now so it can reach the first course and then I will inset it so that it represents an accurate fulcrum.