My intention was to machine an => inch wide groove in the rotor face, maybe .030 to .125 deep leaving a rim around the outer edge ~.020 - .050 inch. Still holding out deciding what to do seeing how this argument plays out. For those keeping score I'm siding with Chris so far. Hard to argue when someone can prove by example it doesn't make a difference.
You could set up the mill and mill out pockets. But it's a lot easier and quicker on the lathe. I've always machined my rotors by facing them so they run perfectly true. I always took .150" off to get all the humps out and get the face of the rotor nice and flat, and left a rim about .050" around the outside for the magnets to butt up against.
On later turbines I went to using bar mags with holes for pins so I didn't do that.
On the ferrite turbines, each one of those magnets weighs over 3/4 lb. I didn't trust the little lip like I've done in the past. The centrifugal forces on those are astronomical when you got a generator running at 1,200 rpm like it does in my latest turbine. So there I welded 1/8" x 3/4" pieces of flat stock to the outside of the rotor to hold the mags against the force. Somebody told me when I posted pictures of the first one that it "steals flux". And that's why I made that video on it. I still haven't found that confounded video. I think it's in my computer with a name like 100-3823.wmv or something and I'm still trying to locate it.
Hah! I found that frickin' video. I'm uploading to YouTube.
OK, here's the video. Later, after I made this video I bought a gauss meter. What I found is that these axial rotors saturate around the edge of the disc and you get flux that leaks because even a 1/2" thick disc will saturate right near the edge. Leaving a "lip" or weld on "claws" only stops the flux that leaks normally anyway, and it doesn't make one iota of difference in airgap flux between the two rotors.
--
Chris