"nlbauers" wrote in message roups.com...

I would need approx. 9 CFM worth of a vacuum press.

"CFM" is an odd sort of measure for a vacuum pump. If it's a vacuum,
they're pretty much running at 0 cfm volume flow by definition. So
this cfm rating is only really relevant in the initial pumping down
stage.

What are you making here ? A device for clamping, or a device for
forming ? Trying to pull it into shape with a vacuum will need a
large volume if it's to be efficient, but once you have the workpiece
to shape and the bag is down, then the flow rate is minuscule, even
for a huge piece. There are people who bag surfboards and model
aircraft wings that are enormous, just working with a fridge pump.
You're not (I assume) a production shop, so you don't really care
about the clamp-closing time, other than to worry about glue working
life.

Can you apply simple mechanical clamping to get the piece to shape,
then enclose it in a smaller bag ? A smaller bag is a cheaper route
to fast clamping than a bigger pump.

If you're vacuuming steam-bent timber (with or without glue) then
you'll be pumping water vapour out for hours afterwards as you freeze
dry it. This may overwhelm a small pump in the early stages.

One thing to watch out for on "vacuum" pumps is that they're rated for
vacuum. Some (fridge compressors) don't like running with zero flow
and can overheat. So either make you bag leakproof enough that you can
switch the pump off when it's under vacuum, or find a real vacuum pump
(probably diaphram or vacuum oil filled). I use an old lab pump (circa
$50 on eBay last time I looked) which will run happily all day and has
adequate volume to hold (but not form) anything. With the aid of
string loops etc. for initial clamping I've never found it inadequate
to hold anything I wanted to make.