I wanted to post a picture of a vacuum from Joe woodworkers website. It is shop made and it vacuums on the top and bottom. So it is locked to your table. Each one of the four areas in the block has a ball bearing valve. When you put on your piece it depresses the ball and pulls a vacuum. I use vacuum clamping and holding in my guitar making. I have a venturi system I built as a kit that runs off my compresser and a continuous run Gast pump I got on ebay for about $60. Both work great a lot faster that hand clamps or screws to hold things down.
@Greenman, Can you post a link to the vacuum clamp and the venturi that you made. Or just post a project for these as there are a lot of us that would like to use this on their tables. Bob
Thanks @Greenman - and my wood/metal/cnc shop thanks you more than you know. Just what I need is another project. YES!!! It is on the list now. Bob
Joe Woodworker is good to work with. His prices aren't a rip. I built the V2 and it was pretty easy works good. I am thinking of building a tanks system for my Gast pump so it doesn't have to run constantly. The other thing he has is a foot switch to turn the vacuum off and on. That is worth checking out.