Ok
It works!
The main ring is of steel, but any tube of reasonable wall thickness is probably ok. The lathe-made hub goes on the central shaft, which is adjustable through the nut fastened on the 2X4 base. I made cuts in the hub to the angle desired. (with Dremell cutting disc) Then the blades are fastened into the spring-loops at the end of the brass-tube made arms.
Then the ring is centered on the shaft, and the blades pushed into the cuts. I used Hydrocloridic acid brushed on the parts, to clean
them for soldering, and then applied heat with a micro torch. Then I added soldering wire, just a tiny amount, to all 3 blades, and a little additional heat. Then some filing, sanding and polishing, and there be propellers!
The blades are made of brass-sheet, with a round steel punch, 8 mm, and 10mm, the desirable 9mm is missing!!
At the moment, the thing most in need of development is the spring-fastener, and the work continues..
Here are some pictures, VII-C sub being the test-subject