The most time-consuming part is the seat.
First, a hoop is made from 1/4 x 1 1/4" hot rolled flat bar.
The hoop is trued up in a form and on a mandrel, by many many hammer blows.
Then, I tack weld it with my wire feed welder turned down low, to a sheet of 18 gauge.
With hoop attached, the shear is used to trim to size, then it's all ground precisely even.
All surfaces have to be very clean and shiny, because the next process, TIG welding, isn't so forgiving of contamination as some. It's important, too, to have a very nice weld where the thin sheet metal joins the rim. This weld is done without added filler metal, so that the rim of the seat is somewhat rounded. Photo at top of post...
(apologies for the photos being out of order- the learning curve, dontcha know)