Well now have the vacuum pump I settled on a 4cfm and a vacuum chamber ( for the resin casting) I have started playing around with making some chucks at the weekend, just awaiting some hardware to assemble the through headstock vacuum tube, and to work out what gauges and valves I will need to control and measure the vacuum produced within the chucks. I decided on three sizes of chuck, 2, 3 and 4" as they should cover most of my initial requirements. if they work ok they are easy enough to make additional sizes.
Many thanks for the advice,