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This article is from Issue 33 of Woodcraft Magazine.
A simple 3-step program to save your waterborne-finish spray gun
By Joe Hurst-Wajszczuk
The lesson typically costs a few good brushes, but woodworkers eventually learn that the success of the next finishing job rides on the cleaning regimen of the last. The same lesson applies to spray guns. A caked-up air nozzle or inlet will cause the best gun to sputter. And, as with a once-favorite brush, by the time you see the warning signs, it may be too late. Some cured finishes are impossible to clean out. An after-the-fact fix may require replacement parts, a pricey rebuild, or a complete spray-gun replacement.
The good news is that prevention is cheap, easy, and quick. Using a cleaning kit (such as Woodcraft #147658) and a few other items, you can clean your gun in the time it takes to clean your favorite paintbrush.
In this three-step program and cleaning guide (see Figure 1, page 40), we’ll help you match the cleaning regimen to the job. Quick mid-project cleanups will mean sputter-free coats, a gun that’s a cinch to clean at the end of the day, and smoother starts for future spray jobs.
Waterbornes vs. Shellac & Lacquer
This story focuses on waterborne finishes because that’s what we use in our shop. Waterbornes’ advantages—low-odor, quick-drying, easy cleanup—made the decision to “go green” a no-brainer. However, it’s important to note one major disadvantage: waterborne resins tend to stick within fluid passages, on the needle, and in the nozzle. Forget to clean your gun, and you’re likely to find it fried the next time you pull the trigger.
The solvents used in shellac and lacquer may be toxic and/or flammable, but they make the guns “self-cleaning.” Fresh finish dissolves the old. Cleaning involves little more than spraying the appropriate thinner through the gun. But unless you have a spray booth, they aren’t the best choice for regular use.
You can spray different finishes through the same gun, but it must be thoroughly cleaned and dried to avoid contamination problems. An easier solution is to buy a second gun. We use a turbine-driven HVLP for waterbornes and a smaller compressor-driven HVLP gun for shellac and lacquer.
Three steps to peak performance
Your cleaning routine begins not at the end of the day, but as soon as your gun starts to sputter.
Step 1: When in doubt, blow it out
At the first sign of trouble, wipe down the air cap with a rag. If that doesn’t do the trick, try a cool clean rinse.
Mid-job cleanup. Replace your gun’s cup with a clean cup filled with cool water. Spray the water into a catch bucket until the water runs clear (Photo A). Wipe down the air cap, switch cups (shown in Figure 1), and you’re back in business.
If your gun still sputters, check the air cap and fluid nozzle for clogs.
End-of-day cleanup. Repeat the step above, and then clean out your cup. Pour out any excess finish and then rinse it out with some soapy water. If the finish has started to stick to the inside, use a fine nonwoven abrasive; just be careful not to scratch through any Teflon coatings.
Give extra attention to the gasket between the cup and gun. Remove any finish buildup (Photo B) so that it does not affect the seal.
Spray warm water until the water is clear. In addition to clearing clogs, flushing the gun will prevent the needle from clogging during lunch breaks.
The gasket seals the cup to the gun. Wiping debris off the gasket now is a lot more convenient than installing a replacement gasket later.
Feed a round brush into the fluid inlet and then into the fluid chamber to snag any finish that might be sticking inside your gun.
Scrub the air cap holes with a small brush. The metal pick has side serrations designed to snag dried finish from the inside of the fluid nozzle.
Step 2: Break it down and brush it out
When you’re done for the day, rinse out the gun and cup as before, and then reach for a brush. The goal is to scrub out the inner workings before the finish has a chance to cure.
Starting from the front of the gun, remove the air cap, fluid nozzle, and fluid needle. Let these parts soak in a soapy bath while you brush out the fluid inlet and fluid chamber with a round bristle brush (Photo C).
When cleaning the air cap and fluid nozzle, do as little as you can get away with. Start by brushing both parts, inside and out. Now inspect the holes. If they look clogged, you’ll need to pick them out. Wooden toothpicks are handy because they can’t damage the metal, but there’s a chance the tip can break and clog the orifice. The mini-brushes and metal picks supplied with the cleaning kit won’t break; just be careful not to damage the metal orifices (Photo D and Inset).
Finally, wipe down the fluid needle. If there’s any stubborn stuck-on finish, step up to lacquer thinner. Avoid using any abrasives that might ruin the tip.
Apply a light coat of grease or silicone-free oil on all threaded or moveable parts before reassembling the gun.
Step 3: Use oil to fix sticks and leaks
You may not need to follow this step every time you clean your gun, but regular lubrication improves the seals and keeps parts from sticking.
A good rule of thumb is to apply a drop or two of oil into the needle packing nut after each use and to lubricate the threads whenever they begin to stick (or before putting your gun away for an extended period). To avoid the chance of finish contamination, avoid getting lubricant on the front-most part of the fluid needle (Photo E).
Make a habit of assembling your gun immediately after cleaning. Not only will this keep the parts together, but storing your gun fully assembled also protects the needle and tip from accidental damage and keeps dust and other potential contaminants from finding their way into the cup.
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