CNC router vacuum tables come in an endless selection of options from a single sheet of MDF with vacuum ports pulling a vacuum through the sheet to a pretty sophisticated layout that is modular and zoned, but before discussing these options, maybe take a quick look at what vacuum pressure is and how we can put it to good use on a CNC wood router.

What is vacuum pressure?

In most “normal” locations in the world, atmospheric pressure exerts 15 (PSI) pounds force on every square inch of surface area. (note this increases at lower elevations and decreases at the top of mountains.

Can we use this for CNC vacuum hold down devises?

Vacuum pressure uses this basic natural phenomenon to its advantage, by removing all the air within an enclosed space forcing the atmospheric air outside to push down into the vacuum space and hold-down  whatever objects are in its path between the natural atmospheric pressure and the artificially created vacuum below.

Think of vacuum packing food. You suck the air out from the inside of the bag.. so you’re creating a vacuum inside, and the atmospheric air pressure outside is pushing the plastic bag tight to the surface of say, your favorite steaks!

In an industrial CNC application where you are trying to create a vacuum hold down, you create a box to contain the vacuum and cap it with the wood or metal that you are trying to machine. By pulling the air out of this box, you suck the piece of wood or metal down to the box's frame.

Calculating the CNC vacuum table pressure.

The dimensions of the surface area where the two engage, determines the strength of the holding power. This is an important point to make in designing CNC vacuum tables; the surface area is one element that controls the pounds of pressure available for workholding.

In a perfect vacuum the pressure will be equal to 15 psi * the width in inches * the length in inches. So if the inside of the box where it meets your work material is 4” x 6” you end up with 15*4*6= 360 lbs of pressure on the material holding it to the frame of the original box.. so sort of the weight of one relatively heavy human being.

Can we get a perfect vacuum?

Now of course this is a pretty simplistic view of things. A perfect vacuum is rarely achieved for a variety of reasons, and often the path of the tool is creating a side load on the work piece doing its best to unseat it from the face of the your box or vacuum pod… so lets look at a few other issues that might affect your success of vacuum clamping before we actually look at how a manufacturer might design a CNC vacuum table.

Friction's Impact on Vacuum Hold Down Devices >>