Time to start making some sort of hub for it..
...starting with a scrap of mild steel bar.
Roughed out with a hole in the middle...

Then turned down a bit of a rusty old bolt for a squeeze fit in the...

...hmmmmmm... not quite as firm as I would have liked but it is snug.
The first bit goes back in the lathe and one hub cheek is roughed out and ...

... parted off.
Here are the bits so far, the rotor wheel, a hub cheek, the original bit of bar used as a mandrel..

.. and of course the bit of old bolt that will be pressed in to hold everything together then sawn off. Loctite in case the fit is not really tight enough?
Everything pressed together and in the vice for the Loctite to cure.

Meanwhile....

... the first bearing cup is being parted off.