Crux

[Ellis]

Agreed, 5mm of Hardox would possibly still be pushing it in terms of sideways-strength, let alone aluminium. I don't know about the high grades of ally, but the lower grades you'd probably be able to bend by hand, let alone with NST's help.

You may need to look into a thick outer ring, something as bend-resistant as Hardox, then you may get away with a high grade aluminium "core", assuming the attachment of the two pieces is up to it. In that case you would have a massive moment of inertia compared to an equal weight solid disc.

Obviously listen to someone who has big spinner experience before heeding my advice, though!