Originally Posted by
stevespo
I don't think your neck laminates will present a problem. I cut loads of belly and pyramid bridges and they have only have a footprint of ~6 sq-in. One thing that will help hugely is indexing your parts with pins which will prevent the parts from twisting on the fixture.
Then the vacuum is only working to resist upward forces from your tools. So depending on your tooling, and how aggressively you are cutting, it might be possible for small parts to lift up and away from your fixture. If you're using straight bits, or downshear, this won't be an issue. Even so, you can get fairly aggressive with multi-flute upcut bits and not run into trouble.
I generally use HDPE fixtures with 1/4" gasketing (set in a channel) and a small 1/5 HP Gast diaphram pump and it has no problems holding down wooden parts during heavy machining. Someday I'll recut these fixtures in aluminum, but any "air tight" material works reasonably well.
Steve