I instructed Grok3 (Elon's AI assistant) to scrape iforgeiron.com and give me the burner spacing for a three burner forge that will be made from a 18" long and 12" in diameter steel tank.

How did it do with the summary and recommendations?

C-  

Following these directions might get you a functioning forge, but there are a lot of missing details that could get you in real trouble. 

15 minutes ago, JHCC said:

C-  

But is the spacing okay?  That's all I asked about. We know there's more to it than this.

For me the starting point is determining the intended use of the forge.  Is this for general forging?  Decorative twists on long stock?  Knowing the intended use can help with determining whether you need to avoid hot spots or if they could be beneficial, for instance.  That can affect burner placement and aim.

Very generally speaking, to me that is a longer forge than I would suggest for typical use.  It can be a bit tricky to get the placement and aim optimized.  We want to keep as much heat in the forge for as long as we reasonably can, so from that point of view it's best to not have the burners so close to the ends that a lot of the heat escapes before we use it.  On the other hand if you want even heat throughout the forge you have to install them close enough to the ends to avoid significant lower temps at the openings.  To make things even more complicated, especially for naturally aspirated single port burners, the flames from one burner can interfere with the performance of another burner.  Naturally, this tends to happen the closer the burners are to each other.

On top of all that, no two DIY forges are exactly the same.  The final shape of the forge chamber affects flame swirl and how exhaust gases escape the forge.  Once again, that can have some impact on how well your burners function and where they should be aimed for best performance.

All of that to say this:  If you are set on building a forge that size using 3 burners, then the general guidelines for spacing you show above are a good starting point.  However, it would be best to build it so you have some flexibility with where the burners are aimed at the very least.  If you are using naturally aspirated burners, the more burners you install the more chance there is for them to interfere with each other's performance - either on the intake side or the flame side.  If you are using forced air this is much less of an issue.

I'm a big fan of the naturally aspirated ribbon burners (NARBs), so if I were doing this project I'd probably use 2 of them evenly spaced between the center and the ends of the forge, and I'd probably mount them on the side of the forge near the top so that the flames would swirl around to the floor. My preferences may not be what's best for you though.