Hello all, I have been reading here for some time and had a few questions. I am new to welding and had struggled to teach myself for years with a Clarke 110 welder. I had some extra funds and Miller had a sale and I bought the 211 autoset. This helped greatly and I was able to see what I was doing wrong and where I needed to adjust. I was given an old tank that has an inside diameter of 20" and is roughly 60" long depending on the rounded ends. It has 5/16ths walls and I found a couple of 5/16ths 4x8 sheets of plate for $100. I have most of the steel and an old trailer to put everything on. I still have some challenges such as lifting it all but do have a small tractor with a FEL. I used the Feldon's calculator and came up with 50.65 square inches of firebox to cooker opening. I multiplied that by 1.5 and came up with 75.97 for the RF adjustment. My 100% firebox size (100.8) is 18.5" cube. I used the circle calculator to come up with a 6' segment height. I was struggling to understand that calculator so I just adjusted the segment height until I got to around 77 ish square inches in opening with an 18.33" cross section. I haven't got to the air intakes or the stack height yet but wanted to check the math so far. As long as I keep my opening to the correct size can I enlarge my fire box? This is not going to be a build thread just at the planning stage. Still have to address cutting everything accurately and maybe getting a decent plasma cutter.