On 6 Dec 2005 15:34:20 -0800, "Tom" wrote:

I have a sherline lathe and want to build a venturi vacuum
generator, to be used with an air compressor. This will be
for vacuum bagging composites.

IMHE, a venturi is the wrong way to make vacuum for vacuum bagging.

A venturi is most efficient when working with a large flow at higher
pressures. It's not the right choice for pumping down to a vacuum (even
when this is merely 1/2 an atmosphere) and when there's negligible flow.
You also need to leave this pump running long term when the resin is
curing, which is annoying with a venturi pump.

IMHO, find a different sort of pump. If the bag is reasonably sealed
then a hand pump or a fridge compressor is perfectly adequate (don't
leave the fridge compressor running permanently though).