Searching the web some more, It seems like 24ga. is the thickest material used for homemade cyclones.
Any thicker than that sounds like it would be hard to shape by hand?
24ga. is too thin for me to weld with my old stick welder!
I could just rivet it together as others have done, But the connection of the cone & upper section could be tricky?
I did manage to find a local sheet metal fabricator that can cut & roll the cone for me out of 16ga. material for around $75, So more than likely I'm probably going to go that route.
Doug