I wasn't planing on using cloth except maybe as a cosmetic wrap.
Carbon fibre also comes in ready made stiff boards and box section, you can laminate the boards/box to the aluminium honeycomb without needing to use a vacuum so it makes life a lot simpler.

Thanks for the offer mekanik it's very kind of you but I'm afraid I chickened out and decided to go for cheapy MDF job as my first build and then get more adventuous in a year or two.

After I've got a machine up and running I might buy enough to make up 50 cm beams of multiple different materials so I can test how each behaves side by side. Seems like a cheaper way of getting a definitive answer to the 'will it really work' question.