I really dont know what is best here. I know really big heat stop joints aren't ideal. Also keep in mind that I dont think you have the angles going the full length of the front and back walls so you will have a step. I dont think a little step will matter much but it will be there. Maybe a piece of flat stock in areas that dont "need" the angle? Maybe beefier angles that go side to side instead of front to back? I don't know. Fewer but thicker angles might be about the same price as more thinner angles. I dont know how either ceiling ties into the door.
There have to be steel suppliers that aren't too far from you. That metal supermarket would have many angles of varying thickness and legs. Flat stock too. Maybe the door fabricator will sell you angle or point you in the direction of a supplier. I just put "steel supplier in Massachusetts" into Google and got a lot of options.
Thank you. So I took some pics of my dry stacked rough draft today. I was thinking of following the earlier models of angle irons running from front to back, but I could also do side to side. I bought another angle iron for the back and yup with it being not as long as the sides, there will be a little step. Fortunately the angle iron thickness is ¼" which will be the thickness of the mortar joints. You can see the gaps in the photos. The red brick will be the landing/vent. With two courses on top of the walls, it spans 14" height, with a 27" wide door (can make 24" in the final mortaring" and 44" depth that the ceiling angle irons have to span.
Priced out at Home Depot they are about $12-15 for the ⅛" 48" angle irons. Good idea about checking the metal supermarket, as it will be nice to have them cut it exact for me. I bought a new Sawzall, so I can if I have to, but it's just one more step. Now do people mortar in between the angle iron and the brick that sits on it? I assume they don't mortar the angle iron down onto the brick it sits on. Or do people not mortar any mortar onto the angle iron? I never really asked and assumed they just stayed in place from the weight. So in my case for the front and back angle irons, do you think mortar is needed on top of or below the angle irons? I really appreciate it! I'm going to try to get all the angle irons in the next few days.
Picture info:
1. The firebricks in the middle front are there just for storage before the rain, but I arranged them more safely before I covered the oven.
2. I placed the firebrick sideways for maximum thickness in the walls. Is this the best way though? It will cut down on oven floor space.
3. The front and side walls have the gap that I can fill in with a cut firebrick.
4. In photo 2, I showed a rough span of the brick, but obviously the brick will be slid over more. I just showed it to show the gap.
My other idea is that if no mortar is needed with the angle iron, then things should line up with ¼" angle iron and ¼" mortar joints.