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A vacuum table is a system for holding workpieces during machining. The device consists of a perforated table top containing a vacuum chamber, and a vacuum pump to keep the vacuum chamber below ambient enough pressure. The workpiece is placed on the top of the vacuum chamber, and thus held down by the pressure differential between the vacuum chamber and the outside air.
A Vacuum Table consists of a typically flat rigid surface in which exists small holes or channels in which to evacuate air from under a workpiece, as to apply varying vacuum from between the desired workpiece and table to maintain a clamping force greater than that needed to machine a part, generally, in a Mill, Lathe, EDM (Electro-Discharge Machine, Pantograph or any other commonly used machine in a machine shop environment.
The main purpose of the Vacuum Table is to allow full access to all sides of a machined part, except the side in which the part contacts Vacuum Table.
A Vacuum Table is similar to a "Magnetic Clamping Table" in use, typically, to the same end as a Vacuum Table except instead of vacuum, the Magnetic Table uses electro-magnetic attraction to restrain ferrous materials to the table facilitating ease of access for modern machining. A Vacuum Table, of course, is not limited to ferrous materials.
The Table works by manipulating atmospheric pressure to provide workpiece force against a surface. This increases static friction against forces of a cutter of various types used today. As atmospheric pressure up to 29 inHg allows clamping force of approx 14 PSI at sea level.
To use a vacuum table one must place the work upon the table and use air dams around the work to minimize lose of vacuum to atmospheric pressure. This maximizes force to the work in any attitude that the table may be held, in all axis, that the work may be machined or inspected.
Air Dams can be nothing more than masking or packing tape, flat stock of just about any material, anything that can resist the vacuum force sufficient to vacuum applied and thus clamping force. Also the Air Dams may provide a closer seal that light vacuum applied to delicate parts can be used.
Air dams are not entirely required in the use of a Vacuum Table but they can be when the source of vacuum is limited. As a vacuum pump, generally, is designed for high vacuum as opposed to high volume, air dams can be used, again, to increase clamping force. A source for vacuum in some applications may be as simple as a typical shop vac or vacuum cleaner, in light application. Vacuum pumps are the usual vacuum source.
Vacuum tables are also used in other industries besides machining. In the furniture business, foam cushions can be stuffed more easily when the foam is compressed previously by the use of a table and a surrounding air resistant fabric. Fabric or film wrapped around the foam allows air to be removed thus shrinking the size of the foam "stuffing" substantially. This smaller foam quickly expands once inside the cushion as the foam obtains equalibrium to atmospheric pressure.