Woodworker's Journal 2011-35-Winter, страница 62

Understanding Spray Guns

Learn the ins and outs of adding a

spray gun to your finishing process.

Compared to the bulk of woodworking, finishing is a rather low-tech endeavor. There's not much investment in tools or equipment unless you decide to spray — at which point the investment can be substantial. If spraying is something you've considered, it makes sense to look at whether or not you really want to go there, what is involved if you do and how to get the best results.

The real advantage to spraying is speed. Spray guns can apply more finish faster to larger or more complicated surfaces than any other method of application. But there is a price for speed. Spraying wastes more material, involves higher equipment costs and uses more electricity than any other application method. Part of the reason is that guns have a relatively low transfer efficiency compared to brushes, pads, rollers and rags. For hobby finishers, spraying is not a necessity. You can be a superb finisher without ever touching a gun, but that doesn't mean you shouldn't. As with all woodworking, spray guns are one of the tools that can help

you achieve an end, and spraying is a technique you might want to have under your belt. That brings up reason number two: spraying is fun. Lots of fun, actually.

How Spray Guns Work

A spray gun works like a carburetor. It forms liquid into tiny droplets and mixes them with moving air to create an airborne mist. Pulling the trigger releases a controlled pattern of air and finish toward the wood. Most guns have controls to change the size and makeup of that mist pattern. The primary controller is the trigger. The further back you pull it, the more fluid is released into the airstream. The large knob at the back of the fluid pin is a governor. By turning it clockwise, you create a stop that limits how far the trigger retracts, which in turn limits the amount of finish flowing through the nozzle.

Either above the fluid knob or to the side of the tip there's usually a smaller knob. This one adjusts the size and shape of the mist pattern. Turn it clockwise to get a smaller, rounder pattern, and turn it counterclockwise for a larger, oval one.

On almost all spray guns, rotating the air cap 90 degrees will change the fan pattern from a horizontal oval to a vertical oval.

Some HVLP guns change from round to oval pattern by rotating the air cap 45 degrees.

Types of Spray Guns: Standard

There are three common types of spray guns sold to woodworkers. Two of them operate in conjunction with a compressor, and the third is powered by a turbine.

Up until the 1980s, the standard spray gun in the field was one that used high pressure compressed air. A standard gun is highly versatile and will spray any material, thick or thin, merely by changing the air pressure going into the gun and the gun's settings. It uses a relatively small volume of compressed air and will work with even a small air compressor. Since it is attached to the compressor via a 3/8" air hose, it is only as portable as the compressor and limited by the length of the hose. Standard guns have a continues on page 64...

62 Understanding Spray Guns