In brief:
Vacuum generators require an air compressor to be running. Noisy, and can use a lot of electricity but should be able to generate near enough 100% vacuum, not that that is necessary or always desirable for a vacuum chuck.
Rotary vane vacuum pumps are generally quiet and small and don't need oil. Can be bought cheaply on ebay, amazon etc. Will run continuously and can generate a vacuum of around 85% - suitable for vacuum chucks but, as stated above, not ideal for resin in vacuum pots.
Reciprocating vacuum pumps (commonly used by refrigeration engineers) generally cost more, need oil, but are quiet and perfectly happy running continuously for 24 hours or more. 100% vacuum makes them suitable for pretty much everything. Can be found second hand in the usual places but generally pretty expensive new (Google Robinair).
Size is not a major factor but most commercially available chucking systems seem to be rated at around 8cbm/hr = 4.5CFM. Less than that will still work but may take time to build up the vacuum.
Similarly, many sources tend to say that a minimum 70% vacuum is necessary.
I made my own rotary adaptor and chucks but hopewoodturning.co.uk is a good starting point for buying them.
Paul Hannaby, oneway.ca, vacuumchuck.com, docgreenwoodturner.com are just some of the many sources of info out there.
FWIW, I made my system more for fun than anything else, but find myself using it far more than I expected, sometimes even with the chucks just used as convenient jam chucks without the pump running.
Duncan
