Now that we have a baseline on the vacuum table performance, time to start performing modifications to see what happens.

The easiest thing to reduce air resistance is to remove layers - we don't strictly need the spoilboard in this setup, so it is removed. We then added some rubber gaskets to improve the seal between the plenum and the fixture, which should reduce air leaking past that particular junction.

[caption id="attachment_5994" align="aligncenter" width="1000"]8 Plenum Gasket Fixture small Spoil board removed, gasket added - 25 inches[/caption]

These modifications did not drop the vacuum of an empty fixture - in fact vacuum was boosted by 2 inches to 25. This implied having the spoilboard in the setup was letting a lot of air slip around the fixture. Removing it was a good call.

[caption id="attachment_6000" align="aligncenter" width="1000"]9 Plenum Gasket Fixture Blanks small Adding work pieces increased to 26 inches.[/caption]

When the work pieces are in place, the vacuum went up another inch to 26 inches. Less air is leaking past the work pieces, and they are now held by about one inch of mercury (roughly half a pound per square inch.)

We haven't put any effort into improving the sealing between the work pieces and the fixture. How much gain can we realistically expect from the effort? In order to get a rough estimate of how much more we might gain, we draped a plastic sheet over the fixture.

[caption id="attachment_6050" align="aligncenter" width="1000"]10 Plenum Gasket Fixture Sheet small Replacing work pieces with a plastic sheet boosted to 27.5 inches.[/caption]

Looks like we have about 1.5 inches of mercury we can gain from better workpiece-to-fixture sealing.

This is a promising start, as this tells us we're in reach of a decently high level of vacuum for work-holding. We now need to put some effort into the other side - improve the path for the vacuum to reach the work pieces and hold them in place.

More improvements to come!