It was a long time ago, so memory of the exact method has faded a little. I certainty cut the discs on the lathe and possibly tidied up some of the ali. soldering on it, but I didn't skim it all over.
I just built it as accurately as I could and took great care in clamping it all square before soldering. Bending was done on a set of home-made rolls made from scaffold tube. Given that it was never balanced, it's remarkably stable. There's a rough spot as it runs up to speed, but once up and running there's virtually no vibration.
Balancing a cast bowl (which would certainly be necessary with a casting) could easily be done on a couple of parallel knife edges, provided the design had a place where metal could be drilled out.
