thanks for the replies, all
and it seemed so simple!
I've thought about making my own blast gates, but think it will only save me about £20 and I can use the time more profitably, so I've gone the bought route - 3 blast gates from Axminster and 2 Y junctions. With clips it comes to about £50 - I've got enough flexible ducting to connect my table saw and woodrat permanently - there's then one pipe left to connect to bandsaw, thicknesser, etc - as these are all on wheels they need to be moved before they can be connected up.
the sudden rush to ducting comes after a day sneezing permanently after an afternoon working with mdf yesterday - i think i need to make my dust extraction as easy as possible...now where's that link from ages ago about remote controlled switching on of an extractor????? :roll:
cheers
Stewart