I designed and built one like that but I didn't like it's design so I scrapped it and built a water-tube for 5HP. Scrapped that one too as it was a prototype. Still have not got round to the third one, need a mill to do some of the cuts for the welds.
Mill does save a lot of grinding
In this case, the mill is a necessity to make regular holes, about 250 holes, which pipe ends fit into and are welded.--the holes are nice fits. My prototype, I cut the holes out with a plasma arc--very sloppy ultimately bad welds, one with a pin hole that I could not get out no matter how I tried. The steam generator, was, however, a success. Reached 100 psi in about 15 min. The next one will be the same design with a few tweeks.
You might like to try the National Railway Museum, York as a first port of call.
