I tried to use my homemade vacuum chuck on a green turned bowl and there was a little warp preventing good seal. I took a piece of plain foam and cut a hole to allow vacuum to reach wood and laid it on the chuck and then the bowl. The extra thickness allowed compression to get a good seal and I could then remove the tenon. Simple trick that I must have picked up somewhere in the past and necessity caused me to try today.
Vacuum Assist 2.JPGVacuum Assist 1.JPG