The holdfast never made sense to me.. why stick a tube through a perfectly good
hollow spindle?

Talk to Bill Noble about used pumps and how to build your own system, or have
him build some of the parts, like the rotary valve..http://www.wbnoble.com/

mac

I concur. Bill Noble helped me a lot when I was building my system.
I ended up with a rotary vane pump that I picked up off of Craig's
list and a bunch of face plates from Bill upon which I mounted various
sizes of PVC pipe for my chucks. I use adhesive backed foam from the
craft store for gaskets.

I never could see why one would want to run a big air compressor to do
the job of a 1/2 HP vacuum pump that will pull more cfm than a
venturi. That cfm is important when you are dealing with a bowl that
has warped.