On flat surfaces paint finishes should be thoroughly brushed out until the covering film is of uniform density, working outward toward the edges to prevent accumulations along the sharp edges. It is always good practice to start each newly loaded brush on the bare wood, brushing into the lap left by the previous brushful. Cross brushing large areas eradicates "holidays" and evenly distributes the film of finishing material. It is always wise to rehearse the initial brush strokes of a finishing job on waste pieces of the basic material, or at least on a piece of wrapping paper. spraying Of recent years the perfection of portable spraying equipment within a moderate price range has popularized the spray finish among home craftsmen Compact outfits, with compressor and motor housed in one unit, are available, and may be used equally well with light or heavybodied liquids. Spray Guns. Certain fundamental differences are built into the various types of spray guns. In the matter of air pressure, guns may be of the bleeder or nonbleeder type. The bleeder type is required where the compressor unit is not equipped with a pressure relief valve, a continuous "bleeding" of air through the spray nozzle aperture being relied upon, after sufficient air pressure has been built up. In the nonbleeding type, no air passes the nozzle until the trigger is squeezed. Another distinction between sprav guns depends upon the method employed to feed the nozzle. Suctionfeed guns create a vacuum in the cup or paint reservoir. FURNITURE FINISHING HEAD CASTING AIR FILTER OIL MOTOR HERE SWITCH Courtesy Tile "DeVilbiss Company Fig. 5.3. Typical modern streamlined portable air compressor. which pulls up light liquids to the nozzle. This type, however, is not so efficient in sucking up heavybodied fluids. In pressurefeed guns compressed air entering the cup pushes theliquid into the nozzle, enabling this type of gun to deliver a uniform amount of liquid under a given air pressure. Courtesy Binks Manufacturing Company Fig. 54a. Nonbleeder externalmis pressurefeed gun. 312 FURNITURE MAKING AND CABINET WORK The cap at the nozzle of the gun mixes air and liquid either internally or externally. The externalmix cap usually has two hooded side ports (A in Figure 5.46) which aim twin jets of compressed air at the atomized mixture leaving the central orifice. This produces the fanshaped pattern so economical for spraying large areas. The internalmix cap has a long narrow slot to fanshape the spray that has been partially atomized by the venturi action behind the nozzle. The externalfeed cap is supplied on both the suction and pressurefeed guns, but the internalmix cap can be used with only pressure feed. Requiring less pressure, it is popular with small units, but is liable to clog with fastdrying mixtures. Spraying Technique. When properly applied to flat work, most guns produce the fan pattern illustrated in the detail in Figure 5.5. It averages about 8 in.