the rails are pre drilled every 60 mm but have been told that i could probably bolt them less hence possibly going less. The hardest thing i will be machining will be ply wood but mainly 90% of the work will be foam. The rail is going directly on the extrusion which is 80X80 ali and using the centring t blocks. More than happy to listen to any other suggestions, i am basically just going by what i have seen on similar machines that have been built with the same intended use.

many thanks charlie