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@Jonny69
Rim purchased. Got a 30mm wide Alex single wall alloy BMX rim in black.
Rough plan is to lay up a pair of skins with the rim on top of the release film inside the vac bag. It should leave a slight indent in the surface which will make centring the two skins a bit easier.
Looking at the strengths and stiffnesses. The M55J UD strength will be about 1700MPa in tension and about 700MPa in compression. That's a bit more than I remembered and much stronger than the woven I had in mind, so I will probably sack off the woven plies. Stiffness is about 290GPa in tension and 260GPa in compression, or about 25-30% stiffer than steel. I think I'm going to lay it up so the fibres run tangentially from the hub rather than radially and alternate the direction with each ply. This gets around needing the woven layer to bind the UD together in the 90 direction. It should be pretty stiff and way strong enough.