flat layup - material and cassette sizes

[sir.orange]

hey
im shaping some new moulds next months and thinking about to switch from prebent, 99% fitting-in-the-mould cassettes, to flat cassettes. till now im using stainless steel and aluminium cassettes, alu 2mm, steel 1mm. all pre-bent fitting the moulds almost exactly.
i do full-length woodcores (3mm tip/tail thickness) with 12mm abs spacers in tip/tail area, laying up in prebent cassettes is a nightmare as you could imagine.

what cassette material and thickness do you recommend for laying up flat?

i heard from ski grace that they re using 3/16 aluminium, trusting my conversion table this is something like 4,6mm...they have ribmoulds so i guess the thickness is required to prevent from waves in the bases. pretty thick piece of metal anyway. i doubt if the bladders of my press would push that sandwich proberly in tip/tail sections, or upgrading my press with some pneumatic rams is necessary!?
i still dont know what my next moulds would look like, massive mdf or ribs, one requirement, the moulds must be adjustable, ribs of course need thicker cassettes...
what is a good material thickness for massive moulds and what is minimum thickness for rib moulds?

[doughboyshredder]

I use 1.2mm for the bottom sheet and .8mm for the top.

I think I would prefer a tad thicker on the bottom sheet.

[falls]

I use 1.6mm on bottom. 1mm on top. Aluminium.
Full MDF molds. The bottom sheet doesn't return to completely flat after pressing, but the top sheet does.

[MontuckyMadman]

18ga all around in al. Returns to flat. Almost.

[knightsofnii]

16ga top and bottom, returns to about 20% of what you bent it, still fine for laying up flat. I think if you want it to come back fully you want spring steel = $$$$$

[chrismp]

2mm thick aluminum sheets...return to almost flat.

[falls]

Prob depends a little on the temper of the aluminium and also the radius it is being bent in to as well.