Termite & Ynneb,
Thanks for the posts.
Yes, the whole thing is attached to a wall. The idea is that, with limited space, the table can be removed, gantry parked at one end and the floor area used for other purposes. I know it's not an ideal arrangement but the need for a larger machine outweighed the other details. A bonus is that any size of material can be placed under the machine - I even had thoughts of students driving their cars under it and doing some serious artwork on the bonnets (trunks?)
I appreciate that the worst case is with the Y axis at its furthest point and that there might be cause for concern with movement but there are a couple of design details that minimise the problem. One, the Y axis motor, and hence its mass, is placed as close to the X axis as possible giving very little moment about the X axis. Two, the intention is to make the whole gantry out of carbon fibre. Composites is one of my interests and it struck me as an ideal material for this type of work as it has very low thermal expansion and is far more rigid than aluminium. Another plus is that the expansion ratios of steel (ballscrews and linear guides) and carbon are closer than steel and aluminium, the two materials most people are using.
I have built a computer controlled oven for baking pre-preg carbon and am confident I can make this work. My initial thoughts are going to be tested out using MDF but will then be replaced as the design gets verified. I know I will have problems with the MDF but at least I can test the structure.
If you have read the other threads you will be aware I have already got the frame made and X axis rails mounted. Just waiting to screw it to the wall now.
Mike