Vacuum Table – Baseline Measurements

The CNC router at Tux-Lab has been under-utilized partly due to its under-performing vacuum table. It has a poor track record on an existing project, and we want to understand why (and hopefully fix the problem) before doing more projects on the CNC router.

To narrow down the cause, we will record the pump’s vacuum gauge reading at various configurations. We use a phone to take a picture identifying the vacuum configuration. We then hold that picture up next to the gauge and take a picture of the phone and the gauge together.

Establish the bounds

First, we get the upper bound: once the pump is up and running, close all the zone valves. The reading – nearly 30 inches of mercury – confirms the pump itself and the majority of the vacuum piping is in good working order.

2 Zone Valves small
Maximum vacuum – nearly 30 inches, good!

The lower bound is obtained by opening all zone valves and place nothing on the spoilboard. When in working configuration, the vacuum will never be weaker than this 7.5 inch reading.

6 Spoilboard small
Minimum vacuum – roughly 7.5 inches.

Most of the tests confirmed that the vacuum setup itself appears to be in good working order. We only started seeing problematic numbers once we started involving the spoilboard and the project fixture. Good news since these are the easiest pieces to fix.

4 Spoilboard Fixture small
Fixture without work pieces – just under 23 inches.

Past runs of the existing project has been done with the fixture mounted on the spoilboard. The vacuum reading of this configuration is surprisingly high at a hair under 23 inches. Indicating a lot of air resistance despite being carved from low density fiberboard.

We then added the work piece blanks on top of the fixture and measured again.

5 Spoilboard Fixture Blanks small
Fixture with work pieces – just over 23 inches.

The vacuum barely changed, to just a hair over 23 inches. This is a problem: it tells us the air can easily find a path around the work pieces so very little of atmospheric pressure is applied to hold pieces in place.

Now the objective is to modify the setup to (1) reduce the vacuum reading of an empty fixture and also (2) increase the vacuum reading of the populated fixture.

Increasing difference between these two readings should increase the holding power.

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