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Tuesday, April 30, 2013

The extraordinary science of the vacuum press

Much of my handmade furniture employs the use of exotic veneers to highlight cabinet sides, drawer fronts etc. In an earlier blog, I talked about how matched veneers can provide decorative opportunities not always available with solid wood alone. The system I use to lay my veneers down is called a vacuum press. It is a very simple device that consists of a large, heavy duty plastic bag measuring 4ft x 8ft with a flat platen inside and a venturi machine that sucks the air out of the bag. The work is placed in the bag, then the air is removed for as long as it takes for the glue to harden. It's that simple.

The part about this whole process that always leaves me amazed is the shear force that is applied through the use of a simple plastic bag. Atmospheric pressure, as I am sure you all remember, is 14 lbs per square inch, so, when you create a vacuum, that is the pressure you apply to a single square inch of surface. There are 144 square inches in a single square foot, so pressure applied to that square foot is approximately 2000 lbs or 1 ton! Therefore, the pressure over the whole 4ft x 8ft bag is a whopping 32 tons!!! No hydrolics, no clamps, no heavy weights, just Mother Earth helping us out.