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Controlling the Spray Gun Pattern for Proper Painting

Since drenching the exterior of a car in a single, simultaneous, smoothly even coat of paint is impossible, it is necessary to paint a vehicle in swathes several inches wide, known technically as strokes. Strokes can be made either horizontally or vertically – horizontal strokes are much more common, and are used for most painting situations, but there are some occasions when a vertical stroke is necessary. The spray gun must be adjusted to each of these situations, which is fortunately a fairly simple operation.

In order to make a horizontal stroke along the panels of a car, a vertical spray pattern is needed – that is, the spray pattern must be tall and narrow. In order to obtain this kind of spray pattern, the air cap must be arranged so that the wing ports are projecting at the 3 o’clock and 9 o’clock positions, parallel to each other on the horizontal plane. In this way, their jets of air pinch in from the sides, squeezing the central spray of paint and air into a vertical lens and simultaneously helping to atomize the paint.

A horizontal spray pattern is needed for a vertical stroke along a car’s surface, with a wide, very short pattern – the exact opposite of the spray pattern for a horizontal stroke. This is achieved by turning the air cap until the wing ports project at 12 o’clock and 6 o’clock, paralleling each other on the vertical plane. Their air then pinches the spray from top and bottom, creating a broad but short lens of paint on the car surface.

Regardless of whether the contemplated stroke is horizontal or vertical, the distance of around 7 inches should be observed for high pressure spray guns, and less for low-pressure varieties. The reason for this is that being too close will “flood” the surface with liquid paint which will result in runs. When further from the surface than 7 inches, or at maximum 8”, the tiny, atomized droplets begin to merge in midair, becoming larger drops which spatter onto the sheet metal. This causes peculiarly knobby “orange peel” paint flaws – a hideous result, best to be avoided.


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