Get a grip on vacuum chucking

Modern Machine Shop, Oct, 1990 by Henry Stier

Get A Grip On Vacuum Chucking

A vacuum chuck is the ideal way to hold many flat, thin or irregular shaped workpieces for machining. The parts may be magnetic or non-magnetic so long as they are not porous.

The power of vacuum to hold something in place was first demonstrated in 1657 in Madgeburg, Germany. One Otto von Guerike managed to fit two hemispheres of copper together and pump the air out of them. They were approximately 18-inches in diameter. Four horses on each side could not pull them apart.

An example of how vacuum chucks may be used to advantage is found in the example of 1/4-inch thick side plates in which some areas were machined down to a 1/16-inch thickness leaving a 1/4-inch island. At first a magnetic chuck was used to hold the plates for milling. Three passes were necessary to remove the required material. The magnetic field held the chips in place and interfered with machining. This led to a poor cutter life and a generally unsatisfactory operation.

By holding the workpieces on a vacuum chuck, the operation was tremendously improved. The parts were machined in one pass and cutter life was improved 100 percent.

Two types of vacuum chucks are commercially available. The universal type has a series of ports which can be closed with screws that seat on "O" rings. Only the holes corresponding to the shape and size of the part to be machined are left open. This system makes it possible to chuck regular or irregular shaped parts. A system of stops and locators permits nesting of parts without any special tooling.

For long run jobs or parts which need heavier machining cuts, special top plates with more open area per square inch are recommended. Since the holding power depends on the atmospheric pressure over the area of the vacuum openings, an "O" ring conforming to the shape of the part provides a maximum holding force. For different parts, the top plate of the chuck easily can be exchanged.

Vacuum chucks are the answer to holding parts for efficient machining in many instances. In some cases, they provide the only means of holding for productive machining.

HENRY STIER 4126 Sheppard Drive, Spartanburg, SC 29301