Small-scale spray-finishing
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Wood Magazine

Small-scale spray-finishing

You've given up on the idea of spray-finishing projects because you think it's too messy, too complicated, and too costly for your small and medium-size projects, maybe you're thinking too big. Airbrushes and some small spray guns cost less than HVLP systems and some full-size spray guns. They reduce overspray and vapor problems when finishing small and medium-size projects, and require only a small compressor or just canned compressed air.

Small sprayers come in three types:

  • Airbrushes, such as the Badger Model 350-4, have nozzles and fluid jars large enough to handle small spray-finishing jobs like jewelry boxes. (See Sources.)
  • Small spray guns, such as the Paasche Model 62-2-3 and the K-Grip Siphon Gun sprayer, hold and spray more finish than airbrushes, but less than most intermediate spray guns.
  • Touch-up spray guns, such as the Speedaire 4RR06 (Sources), handle large projects, such as cabinets and furniture, but they still require less air than full-size spray guns.

Airbrush small projects
Airbrushes may seem too small to be practical, but they have advantages. There's less overspray waste on small projects or projects with narrow parts, as shown above. Despite their diminutive size, airbrushes can shoot light-body stains, thinned and some unthinned lacquers, shellac, thinned varnishes, plus water-based finishes. The material needs to be the consistency of skim milk or thinner.

To handle these finishes, select an airbrush with the largest available nozzle and a container that holds 3/4 to 2 oz of material. Choose an external-mix, single-action airbrush that mixes the finish and air outside the body of the airbrush and on which the trigger controls just the release of finish, not finish and air flow.

Next, choose an air source that suits your spraying plans. An airbrush can operate off air sources as simple as a compressed air tank you can refill at a gas station. A light-weight tankless inflater provides a constant air supply, as will portable tank-type air compressors sold at home centers for powering pneumatic nailers.

Sources
Airbrushes: Badger 350-4 set with three nozzles, hose, and two jars, from webairbrushes.com, 888-499-6996. Badger Air-Brush Co., 800-247-2787 or badgerairbrush.com. H-Card model set, from Paasche Airbrush, 773-867-9191 or paascheairbrush.com.

Small sprayers: K-Grip Siphon Gun sprayer, from Woodcraft Supply (no. 149425), 800-225-1153 or woodcraft.com. Model 62-2-3, from Paasche Airbrush.

Touch-up spray gun: Speedaire 4RR06, from Grainger, 800-323-0620, grainger.com.


 

How to read an airbrush pattern

How to read an airbrush pattern

Before spraying your project, practice on cardboard to adjust the finish viscosity and airbrush settings. If you're using an air compressor, set the pressure reaching the nozzle to 25-30 pounds per square inch (psi). Spray a short burst of finish, and then adjust the fluid flow using your results against the examples shown in the chart right. Airbrushes produce a conical spray pattern that can be narrowed by holding the airbrush closer to your work and reducing the fluid flow.


 

Small guns for larger jobs
Spraying half round table top
Enlarge Image
 
For spraying water-based finishes,
a box fan with a furnace filter taped
to the intake side directs odors
toward the nearest window.

Small guns for larger jobs

For larger projects, consider a small spray gun with greater finish storage capacity and a larger fan pattern than an airbrush but with lower air requirements and less overspray than an intermediate spray gun.

For greater versatility, look for models that allow you to control the fluid flow in addition to regulating the air flow at the compressor, such as the K-Grip Siphon Gun sprayer. By using canning jars to store finish and as the fluid reservoir -- coupled with a simple siphon action that mixes air and fluid outside the gun -- the K-Grip cleans up quickly.

Small sprayers often call for compressors that generate 3 cubic feet per minute (CFM) or more at 90 psi, although we sprayed small projects with the K-Grip using an air compressor producing just 2.4 CFM. The K-Grip needs as little as 20 psi to spray lacquers and 25 psi for polyurethane.

Just a touch-up larger
Stepping up to a touch-up spray gun gives you more control over the pattern. Unlike airbrushes and some spray guns, touch-up sprayers produce a fan pattern instead of a conical shape. You can dial in a wide fan pattern to spray a cabinet side or tabletop, as shown above, or tighten the pattern to finish narrow table legs. Customizing the pattern conserves finish material by reducing overspray.

Two other features of touch-up spray guns also let you work faster: Their greater fluid capacity means less refilling when spraying larger projects, and by using larger nozzle sizes than a small sprayer, heavier-body finishes, such as varnish and shellac, can be sprayed with little or no thinning. That means you can spray two or three heavy coats instead of four or more thin ones.

Unlike full-size spray guns, a touch-up sprayer's 3.5-CFM requirements could be met by a 2.6-gallon portable compressor. Even when touch-up sprayers specify an air source requirement like 3 CFM at 90 PSI, most finishing jobs require far less pressure. Thinning may help a slightly undersized air compressor atomize a finish while reducing air use. Lower air pressure also reduces ?bounceback? -- droplets of finish that ricochet off the surface you're spraying.


 

Set up a spray space

Set up a spray space

The smaller the spray gun, the smaller the work area you'll need. But even a touch-up sprayer can be dialed back to apply water-based finish in a tabletop spray booth made from a large cardboard box.

Whether spraying water-based or flammable finishes indoors, position a fan to draw fresh air into the space, around your workpiece, and toward a window or door without pointing the fan directly at your workpiece. Avoid drawing flammable vapors into the fan motor, where they could be ignited. And wear a respirator made to filter organic vapors.

Then arrange a low-angle light to reflect where your finish lands and call attention to any missed spots. To make small and medium-size projects easier to rotate for spraying, place them on pieces of cardboard or a turntable.


 

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