Vacuum damping is a reliable and simple way to fasten templates and workpieces together. The systems shown in this section of the chapter offer as much holding power as mechanical clamps and greater convenience with
out risk of damage to the stock. The only requirement is that mating surfaces be flat and smooth.
There are two common vacuumclamping systems. The venturi system (below) is relatively inexpensive to set
up, but you will need a compressor with */:-horsepower capable of delivering 60 to 80 PSI. The system shown on page 82 relies on a vacuum pump rated at 3 cubic feet per minute or higher. In either case, vacuum tape is fastened to both sides of a commercially available bench plate, which is capable of clamping on two sides. The plate is then sandwiched between the workpiece and template. The tubing from the venturi or pump is attached to the outlets on the bench plate—one for the workpiece side and one for the template side. The venturi or pump then sucks air from cavities on both sides.
The setup shown at left relies on three vacuum tubes to hold a drawer side against a commercial dovetail jig. Two of the tubes are connected to an L-shaped vacuum-clamping jig; the vertical section holds the workpiece in position and the base secures the entire assembly to the bench. The vacuum tube connected to the dovetail jig’s backing board fastens the jig to the workpiece.
Preparing the bench plate
Apply four strips of closed-cell vacuum tape to each side of the bench plate, forming a rectangle with no gaps (above). Next, screw the fittings at the ends of the tubes from the vacuum source to the outlets on the bench plate.
Anchoring the workpiece and template to the bench plate
Cut the workpiece roughly to size, then set it on a work surface. Position the bench plate on the stock, making sure the tape strips are flat on the workpiece. Turn on the vacuum source to the work piece-side of the bench plate and press the plate on the workpiece to seal the vacuum. Air pressure will hold the two together. Next, position the template on the bench plate (left), aligning the straight edges of the template and the workpiece. Turn on the vacuum to the template-side of the bench plate and press down to attach the pattern to the plate.
The vacuum clamping system illustrated at right is similar to the venturi method presented on page 78, except that it relies on a pump as a vacuum source. The model shown is a – horsepower oilless pump, which draws air at a maximum of 4.5 cubic feet per minute. The hose features a quick coupler that attaches to a commercial bench plate or to a connector that is screwed into a hole through the template. The vacuum tape seals the cavity between the template and workpiece, or between the bench plate and the workpiece and template.
BUILD IT YOURSELF
A VACUUM TABLE
As an alternative to clamping a workpiece to a bench, the vacuum table shown below can secure a workpiece for edge shaping with a hand-held router. With no clamps to get in the way of the router, this system offers more convenience than conventional clamping.
For the top, cut a piece of plastic laminate and glue it down to a base of 3/i-inch plywood as you would for a shop-built router table (page 40).
You can make the pieces any suitable size, but cutting them 8 inches wide by 16 inches long will produce 1,280 pounds of clamping force. Drill a hole through the top near one edge and midway between the ends; size the hole for a threaded hose connector and fasten the connector to the top from underneath. Screw a solid-wood l-by-2 spacer as long as the top is wide to the top’s underside along each end; the outside edges of the spacers should be flush with the ends of the top.
Next, apply four strips of vacuum tape around the perimeter of the top, forming a rectangular cavity; make sure that there are no gaps between the strips.
Tn use the vacuum table, secure it to your workbench and center the workpiece on the table, ensuring that the tape strips make solid contact with the stock. Turn on your vacuum source, then use a router fitted with a bottom-piloted bit to shape the edges of the workpi6ce, making sure to keep the pilot bearing pressed against the edge of the stock throughout the operation (above).