I start with a 3/4" copper pipe cap
And some 5/16", .014" wall brass tubing
A 5/16" drill bit...........
......and our cap chucked up in the vise, gives us a hole that will take the brass tubing, AND allow us to insert a 5/16" bolt onto which we will thread a nut.
Now we have a way to turn the cap in our tubing cutter. I aim for somewhere around a 1/2" to 5/8" deep cup. Sometimes the piece seems to walk in the cutter so it's never an exact science for me.
Now I'll take my tubing and using a tubing flare set make a single flare
Now I'll just gauge my cup and mark where to cut my tubing.
This is a tight enough fit that a gentle tap from a hammer may be needed to seat the brass into the copper.
And I'll usually pound the metal flush for a good tight fit
Solder, cup, and torch...........
Make sure to heat primarily the copper. The brass is super thin and will get hot all by itself.
A little dressing with a couple of files
Flattened the bottom out nicely.......
And it fits perfectly over a 200a generator.
One of our German collectors friends with the appropriate skills and equipment had cups milled from flat aluminum plates. One version to slide over the generator and one version for the MilSpecs (Those are very popular with our collectors).
Here some pics:
Pls. see navigation on HP for Collectors Maps.