Designing a better bed

[D.C.]

The standard approach to a moving gantry CNC bed seems to be a thick piece of aluminium preferably 20mm or more.
Aluminium is expensive, the cost for my bed in aluminium plate would be £338.

With that budget in mind I've been trying to design something better for less money in materials, assuming that I work for free.
Lots of head scratching and reading up on torsion boxes, stressed skin panels, constrained layer damping etc etc This is where I am at now.



The sides of the bed are 3mmx80mm steel plate.
The bottom is 3mm steel plate.
The reinforcing is 20mm x 20mm hollow steel square.

After much reading about the wondrous technology of constrained layer damping, it turns out that one of the very best 'viscoelastic damping materials' is butyl and it needs to 0.5mm to 1mm for the sort of things we do.

Which is handy, because the super spiffy viscoelastic wonder material has another name - pond liner. 0.75mm pure butyl pond liner is about £7 per square metre.
So all of the reinforcing will be wrapped in pond liner, sorry, (viscoelastic damping membrane.)

After that the bed will be filled with carbonfibre reinforced epoxy quartz and vibrated, the top couple of mm will be pure epoxy so that it self levels.

The quartz I can get from http://resinbondedaggregates.com/ they wash, grade and kiln dry quartz specifically for resin work. About 20p per kilo.
The epoxy is IN2 infusion resin with a slow setting hardener, £72 for 5kg from easycomposites.
The carbonfibre is £47 for 2kg from easycomposites.

So the original budget of £338 for 20mm aluminium now breaks down to

£90 in steel
£10 in pond liner
£140 in epoxy
£20 in milled carbon
£25 in aggregate

£285 total

I've been very generous with the epoxy as that is the scary expensive part, £140 assumes an 18% by volume mix but hopefully it will average out lower than that. I could still go to almost 25% epoxy and break even with the aluminium.

Any thoughts or comments on this approach for a DIY bed?