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The small, concentric rings of alternating woods in the knobs for this desk are another expression of the "detail-within-detail" concept that I tried to maintain throughout the design. (See photo. page 4h.) Though they look expensive, these custom-made knobs can be made quickly and easily. All you need is a drill press, some dowel rod and a supply of standard, store-bought knobs with round tenons.

Step 1: Clamp a flat piece of scrap stock to the drill-press table and drill an alignment hole, using a bit « « ...

that matches the diameter the top of the maple knob. of the knob's tenon.

Step 2: Fit the knob in the hole. Then chuck a '/2-in. Forstner bit in the drill press and bore into the top of the knob. The bit should leave a clean, centered hole about 5/8 in. deep. (Make sure not to weaken the knob by drilling too close to its waist.)

Step 3: Glue a '/2-in.-dia. walnut plug in the hole, keeping the grain consistent with the knob. Trim and sand the plug so that it's about Vl6 in. proud of the knob, and curved to match its contour.

Step 4: With the knob in its alignment hole, bore a 3/16-in.-dia., 7/8-in.-deep hole in the walnut plug. Then glue in a 3/16-in.-dia. maple plug. Trim and sand this plug to a rounded button about Vl6 in. proud of the walnut surface.

Step 5: Chuck the knob in the drill press, adjust speed to around 800 rpm, and use a piece of steel wool (000 or finer) to smooth the concentric plugs. The heat caused by the friction will darken the maple and give the entire top of the knob a beautiful patina. —R.L.

Second hole. After gluing a walnut plug in the knob, Lay port lx)res the hole for a 3/1(>-in.-dia. maple plug.

Final spin. With both plugs glued and trimmed, Lay port chucks the knob in the drill press and smooths the bull's-eye with steel wool.

Buyer's Guide to Vacuum Veneering

Let Atmospheric Pressure Put the Squeeze on Your Work with One of These Affordabley Easy-to-Use Systems

By Jeff Jewitt

In my cabinctmaking business, I've traditionally relied on solid wood for most of the pieces 1 make. But in the past several years, solid wood has bccomc more costly and exotic species arc difficult to find. I've seen some beautiful veneer work done by large shops, but the prospect of setting up a big screw-type press to produce veneered panels was daunting. Other veneering tcchniqucs have their draw backs as well: I never quite got the hang of hammer-veneering and I don't trust the adhesive bond you get when veneering with contact cement.

Then I discovered vacuum-bag veneering. Vacuum-bag systems arc simple, affordable and nearly foolproof. Even a first-time operator can clamp complex work such as curved panels. And when you're finished, the whole system can be packed up and stored in a small space.

A number of companies sell vacuum-bag veneering systems or "vacuum presses" ranging in price from under $200 to several thousand dollars. Specifications for 16 different systems for woodworkers arc shown in the chart on page 53. For this Buyer's Guide, I tested 1 1 of these systems that arc priced under $1,000. The systems I didn't test arc constructed in the same way, but they differ in capacity. Before

Airing out. A vacuum veneer press makes quick w ork of c lamping curves. Here the author smooths the vinyl hag around the form as the pump sucks out the air.

Pumps, bags and fittings. There are three different types of pumps for vacuum pressing. All three use similar vacuum bags and fittings. Left to right: a 5-cfm automatic venturi, a 5-cfm electric pump, and a 2.2-cfm manual venturi.

I gcc into the details of what I learned in my tests, let's take a look at how a vacuum press works.

Vacuum Pressing Demystified

There are three basic parts to a vacuum press: a vacuum pump, a vacuum bag and a gridded platen on which you place the work. Manufacturers supply pumps and bags in different capacities and combinations depending on your needs, but you have to make your own platen. This is done by cutting a grid of shallow (Va-in.) saw kerfs into a piece of V4-in. melamine or similar nonstick material. The kerfs provide air paths so the pump can evacuate all the air from the bag.

Using a vacuum press is easy. For flat work, prepare your substrate (core material) and veneer, then make a caul the same size as the veneer and lay it on top to protccr the veneer. Spread your glue on the substrate, lay the veneer on the glued surface, position the caul and slide this "sandwich" onto the platen inside the bag. Seal the bag and turn on the vacuum pump.

From here, the laws of physics take over. As the air is evacuated from the bag, atmospheric pressure bears down on the bag and its contents like a giant clamp, pressing uniformly with a force of more than tons per square ft. It's stone simple. The uniform pressure prevents the veneer from slipping around, as it easily can in a conventional clamp-based veneer press. And the vacuum also promotes good adhesion by sucking the glue into the pores of the veneer and substrate.

Vacuum veneering isn't just for flat work. It's also great for curvcd gluc-ups since there's no need to fabricate both male and female forms. The vacuum clamping process exerts even pressure, no matter how complex the curvature.

The manufacturers listed in the chart sell complete vacuum-bag veneering systems that include a pump, a bag and necessary hoses and hardware. They all also sell individual components. To choose the system that's best for your woodworking needs, you'll need to select the right components and compare prices.

Choosing a Pump

The heart of a vacuum press is the pump, and there arc two general types: electric and venturi.

Electric pumps draw air out of the bag like small vacuum cleaners. These pumps arc available in different sizes, rated by cfm (cubic feet per minute). Large 10-cfm pumps arc best for production veneering or quick evacuation of large bags. A 5-cfm pump will suit most small shops doing custom work.

Venturi pumps work differently. In these, compressed air supplied by your compressor rushes through an orifice to generate a vacuum. Since they have no moving parts, venturi pumps are less expensive than electric pumps. Venturi pumps come in automatic and manual models. All bags leak air to some degree, and an automatic venturi pump turns on automatically to restore the vacuum when it falls below a preset limit. (That's important, because slow-setting glues such as urea formaldehyde take hours to set and the automatic control frees you to concentrate on other work.)

With a manual venturi pump9 you monitor the vacuum yourself by checking an attached gauge. To restore lost vacuum, you manually open a valve on the pump body. Vacuum veneering with a manual venturi pump is more work, but these "bare-bones" pumps cost hundreds less than most automatic pumps. With a manual pump, you can set up a system for as little as $200.

Venturi pumps arc also rated in cfm and need to be matched to a properly sized compressor. (Sec chart.) For example, a 10-cfm venturi pump requires a 4-HP compressor, while a 1.8-cfm pump will work with a 1 -HP compressor. (A large pump on a small compressor will overwork the compressor.)

I tested electric pumps rated at 5 cfm from four different companies. (Sec chart.) These pumps evacuated my 4-ft. by 6-ft. vacuum bag in about one minute. Speed like this is a good feature if you're doing production veneering.

With an evacuation time of about six minutes, the 1-cfm continuous-running diaphragm pump from Vacuum Pressing Systems is a unit I'd only recommend for occasional use. (Note: Bag evacuation times should be considered approximate, as actual time depends upon the bag size, the type of work being pressed and the condition of the bag.)

1 liked the three automatic venturi pumps 1 tested. The units from Vacuum Pressing Systems (3.2 cfm) and Mercury Vacuum Presses (4.9 cfm) arc solidly built and worked well. Each of these units comes with removable filters for vacuum and compressed-air lines. The filters trap sawdust and other minute debris.

I hc automatic venturi pump I tested from Quality VAKuum Products (1.8 cfm) is constructed of lighter-gauge steel and has no removable filters. I found that a small ball of steel wool placed in the vacuum line did a good job of filtering debris, as the manufacturer suggested. I had to adjust the pressure settings on my compressor to get this pump running properly. But this pump is priced low

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