Dialing in your spray gun follows a methodical process of testing and adjustment. Here’s how to do it:

1. Prepare Your Finish: Thin your finish to the manufacturer's recommended viscosity. Use a viscosity cup to measure the time it takes for the finish to drain—this is your viscosity in seconds.
2. Set Initial Gun Settings: Start with the manufacturer's recommended air pressure and nozzle size for your chosen finish. A 1.4mm nozzle is a versatile starting point for many clear coats.
3. Test on a Scrap Piece: Always test your spray pattern on a piece of cardboard or scrap wood before spraying your project. Hold the gun at your desired distance (typically 6-8 inches).
4. Analyze the Pattern: Spray a short burst. A good pattern should be an even, elongated oval with soft edges and no heavy spots or "tails."
5. Adjust and Retest:
   • If the pattern is too round, increase the fan control.
   • If you see "orange peel" texture, the finish may be too thick or air pressure too low.
   • If the finish is running or sagging, you are moving too slowly or are too close to the surface.
6. Determine Overlap: Once the pattern is good, determine your overlap. For a 6-inch wide fan, you should overlap each pass by about 3 inches (50%) for even coverage.

• Spray Pattern (or Fan): The shape of the finish as it leaves the spray gun nozzle. It can be adjusted from a round circle to a wide, flat fan.
• Atomization: The process of breaking a liquid finish into a fine mist of tiny droplets. Proper atomization is key to a smooth finish.
• Viscosity: A measure of a fluid's resistance to flow. In finishing, it's often measured in seconds using a viscosity cup.
• Overspray: Finish particles that do not land on the target surface, creating waste and a messy work area.
• Transfer Efficiency: The percentage of finish that actually lands on the workpiece compared to the total amount sprayed. HVLP guns have high transfer efficiency.
• HVLP (High Volume, Low Pressure): A type of spray gun that uses a high volume of air at low pressure to atomize the finish, resulting in high transfer efficiency and less overspray.

"Your spray gun is a precision instrument, but it's only as good as your technique. The single most important aspect of good spray technique is consistency. Your distance from the surface, your speed of movement, and your overlap must be exactly the same for every single pass. Any variation will show up in the final finish as a light or heavy spot. Practice on scrap until the motion becomes muscle memory. A smooth, robotic consistency is what separates an amateur finish from a professional one." - Professional Automotive and Furniture Finisher

Spraying Kitchen Cabinet Doors: You are using an HVLP gun with a 1.4mm nozzle to spray water-based lacquer on vertical cabinet doors.
The calculator will recommend a spray distance of about 6-8 inches, a 50% overlap, and a steady hand speed. It will also remind you to keep the gun perfectly perpendicular to the surface to avoid uneven application on the edges.

Finishing a Large, Flat Tabletop: You are using a conventional spray gun to apply polyurethane to a horizontal tabletop.
The calculator might suggest a slightly larger nozzle (e.g., 1.6mm) and a wider fan pattern to cover the large surface efficiently. It will recommend a 40-50% overlap and a consistent walking speed to maintain an even coat across the entire length of the table.

• Arcing the Gun: Swinging the spray gun in an arc with your arm instead of moving your whole body results in a heavy coat in the middle and thin coats on the ends.
• Incorrect Viscosity: Failing to properly thin the finish is a primary cause of "orange peel" texture and poor atomization.
• Forgetting to Strain the Finish: Small, undissolved bits of finish or contaminants can clog the spray gun nozzle, leading to a sputtering, uneven pattern.
• Insufficient Air Pressure: Too little PSI will fail to atomize the finish properly, resulting in large, wet droplets and a blotchy surface.

• Cabinetry and Furniture: Achieving a professional, factory-like finish on custom-built pieces.
• Automotive Painting: Dialing in the perfect spray pattern for applying primers, base coats, and clear coats to vehicles.
• Architectural Coatings: Efficiently painting large surfaces like doors, trim, and walls with an airless sprayer.
• Hobbyist Finishing: Helping beginners understand the variables involved in spray finishing to reduce frustration and material waste.