Come on, Simone. Let's talk about your big butress.

[Zimmy]

Pee Wee Herman must have been mistaken, as not everyone here has a big butress. In fact most of the builds I see here do not have them.

I'm at the point with my arch design where I need to choose semi-circular or straight sides with a shallow arch. I see lots of comments about the straight-sided approach needing buttressing, but hardly anyone actually doing it. I must admit, I like the more refined look of three courses of vertical bricks with a shallower arch on top. But I am building a high dome/hemispherical igloo-style oven, so maybe a semicircular arch entry will better match the aesthetic of the design? And I am in SoCal earthquake country so strength to withstand movement is a real concern. I am not building an enclosure, so the extra bulk of butresses will really be noticeable. Let's discuss.

[david s]

Buttressing will increase strength (good), but also increase the heat sink effect (bad) that can be mitigated to some extent by separating the whole flue gallery from the dome.
Because the flue gallery sees lower temperatures than the dome, thermal expansion is lower which reduces potential damage. Brick galleries are more susceptible than cast ones because of their mortar separated units.
For these reasons I believe a cast gallery or fabricated stainless steel one are superior solutions to a gallery made using brick units.
But there are a myriad of solutions, largely determined by personal preferences.

[JRPizza]

You've probably already seen that I'm a fan of the hemispherical arch. Below I took the recommended dimensions for a 36 and 42" oven from the Forno Bravo plans and interpolated for my 39 inch oven ( roughly a meter and I think perfect size) as well as your 37.5
Your numbers would come out to about a arch opening of 19.25 inch wide and ~12 1/8 high. That width would give a natural radius of about 9 5/8.. If you start your arch radius sitting on top of a 2.5 inch untapered brick, you would get a opening of exactly 12 1/8 (not counting for thin mortar layer). You can build a flat arch if you want, but I think the numbers are trying to tell you something!

			Opening	Opening	Ratio
Inch	ID	Height	Width	Height
36	36	18	19	12	66.67%
37.5	37.5	18.75	19.25	12.125	64.67%
39	39	19.5	19.5	12.25	62.82%
42	42	21	20	12.5	59.52%

[JRPizza]

This picture kinda shows what I was trying to describe with the untapered bricks at the arch base and the arch radius starting at the top of those bricks.

[Zimmy]

Those tapered bricks look amazing. I don't think my wet saw is nearly big enough to cut in the 4-1/2 inch brick direction, so I'll have to go with wedges in my mortar joints. I do want to figure out how to make a nice oversized keystone for the top of the decorative arch, though

[Gulf]

You can cut part way through and then turn the brick over and cut from the other. It will probably leave a small section in the middle that is not cut entirely through, but a light tap will finish the job. I have done it free hand. However, clamping an angled guide to the tile saw will make things much easier.

[JRPizza]

I tried to walk through the process of cutting the arch bricks in my build thread - it was really not that hard and I think the look is worth the trouble. I had to flip the bricks over but was able to cut them all the way through in two passes. Just cut them all from one side, then adjusted the jig and did teh second pass. I also used the same angles for the inner and outer arches.