hmm. I don't want to be causing arguements on here.
a few notes.
Please see attached at diagram, showing the coefficients of linear expansion for some common materials. I know, there are other ingredients in both solder and brazing rods, but the main ingredient of solder is normally either lead or silver, with coefficients of 29.3 and 18.8 respectively. Then note that Brass, is 18.9. Plumbing solder is normally lead based, so has a much hgher expansion rate than the brass. Expansion won't be a problem for the brass.
A weld (more specifically a mig weld because it is bigger, although I have tig facility as well it's just a lot more expesive buying pure argon and i like to save it for the turbo exhaust manifolds i make) will also have a different expansion rate to the base material because it has more material. More material, more expansion for the same rise in temperature.
Secondly. I made the immersion heater boss for Ged's by hand in the lathe. It's made from hex bar that I had big enough, I bored it out and screw cut it, and parted it off at 10mm deep so that I could use the same piece to do one for my own drum. I then drilled a 12mm hole into the drum, and using two thick round disks which I bolted through the drum (one inside and one outside) I flattened the drum side to match the flatness of the immersion thread. The hole was then made with a hole saw and I tig welded the thread to it. Unfortunately at the time I hadn't got a blank to be able to leak test the weld on the thread (I leak tested the cone before doing the thread) so I got my work mate to braze around it as well to be doubly safe. Unfortunately his brazing isnt as tidy as mine, but that's a different story. I now have a blank which I used today to test mine.
I'm not sure what your background is, and it's not my my place to assume, but I hope that if you're qualified enough to tell me that my method won't work, you will also be able to see the reasoning behind why I did it this way and give me reasons why. I have far from "not thought it through"
