This written below was first written in 2002, it is not the perfect paint gun adjusting solution but it will give you an understanding as to why you should adjust your gun and some starting points.
PLEASE feel free to add any ideas that that may help!
This may sound trivial to an experienced painter but the fact is very few painters know how to adjust their paint gun. This one item separates a sprayer from a painter more than anything else. The fact is a painter that knows how to fine tune his paint gun will turn a lot more hours and have a lot less problems because he is controlling the paint and is not letting the paint control him. This is why 80-90% of the painters today hate to spray High Solids clears. They vision runs or orange peel and if you don’t adjust the gun properly this is what you will get make no doubt about it.
First of all the number one question I get is what tip should I use? My personal feeling is for basecoat a 1.3 or 1.4 and for clear 1.4. The exception on the 1.4 for spraying clear would be certain HVLP guns where a 1.5 is made for spraying clear. And of course a true painter is only going to use gravity feed gun. Leave the old siphon feed guns for the enamel sprayers that they are made for, as these guns have no place in today’s body shops that are using Urethanes and Polyurethane’s.
What happens with an improperly adjusted paint gun?
If you’re applying basecoat chances are you’re applying it way too heavy and your blends are showing, your metallic are not lying down or standing out like they should so your color marches are a problem and the base is drying slower between coats than it should.
The number one clue the basecoat is going on too heavy is if you’re having a die-back problem with the clear after setting overnight (trapped solvents).
If you’re applying clear the clear is controlling you instead of you controlling the clear. With a High Solids clear you try to spray it wet enough that the orange peel will flow out but hope that it doesn’t flow so much that it runs on you. The next day you tend to have a clear that looks cloudy or milky because of the trapped solvents and it requires a lot of wet sanding.
The benefits of adjusting the paint gun properly will be faster application of paint and you will know what the final job will look like when you spray it and not have to guess.
How do I properly adjust my gun?
Place a piece of masking paper on the wall, then set the fan how you like it. Adjust the air pressure to the rate that you plan to spray with. Screw in the fluid adjustment all the way. Hold the gun from the paper the distance that you would normally spray (usually 6-8 inches) and give the trigger a quick squeeze and release. If anything comes out of the gun it should be very little and dry.
Turn the fluid out one full turn and repeat this procedure half a turn at a time until you are getting an even pattern and the paint is even in build. If it is metallic the metallic should spray even as well.
At this point go to a rocker or bottom of a fender on the car and make a 12-inch pass. You will most likely have to back the fluid out one-half to one full turn to spray at the speed you want then fine tune your air pressure.
Now the gun is very close in adjustment, you should be able to lay the clear orange peel free with out running it, and metallic should spray even and wet with out much effort. Keep in mind this is not your last adjustment; every base color will spray a little different and may require a half a turn in or out for the new color. If you're going from a high solids clear for an all-over to a spot repair clear you will need to make a minor adjustment again.
A simple formula to remember is orange peel is fluid adjustment and run control is an air pressure adjustment. If you’re getting a few runs try upping the air pressure 5-10 pounds more.
One final note, spend the money for a good set of paint guns! This is your career and the paint gun makes or breaks you as far as labor hours turned. NASCAR drivers don’t buy their race engines at a parts store to save money, so why would a painter want a $200 gun? Spent the $400-600 for a good base gun and again for a good clear gun the payback will be faster than you think. You will always get what you pay for with a paint gun!