The type of gun that you shoot paint with is very important as it will determine the quality of the paint finish. There's a few different types of guns out there and here's where you'll find out the differences.
Air Brush Gun
The air brush gun is used to paint murals and special effects on cars. It produces a fine spray and is more of an artist tool.
Touch Up or Detail Gun
The touch-up or detail gun is used exactly as its name implies. It is for touching up small pieces and correcting errors in paint. It is also used for difficult areas to paint such as the dash of my Pontiac. I used a new touch-up gun that I purchased from Princess Auto. Normally it was $45 but on sale for $15. It works like a dream except that I didn't check to see if all the fittings were tight. On the last coat, it spit a small drop of paint on the inside of the glove box cause one of the fittings loosened up. I'm not too worried as it'll be hidden by the glove box door. I'll leave the paint spit as a reminder of my first real paint job. The touch up gun holds 1 pint of paint and it took about 1 pint to paint 3 coats on the dash. I filled the gun for each coat as I didn't want to tilt the gun and suck air in by accident.
External Pot Spray Gun
I first bought one of these as I thought that it would be great as I wouldn't have to fill the pot up so often as it's huge. I never used it and sold it right after buying it. The problem is how do you clean the hoses? This gun is used for painting large objects like buses and in woodworking where all you do all day long is paint gallons of paint at a time. Maybe I should of tried it...
Older High Pressure Spray Gun
The older spray guns use a high air pressure to operate at. They were "good" in their day and you can lay down a pretty nice paint job with them. The problem is that the high pressure causes lots of overspray in the air. This causes two problems:
Binks Style Spray Gun
The one shown above is a "Binks" style spray gun that is a non spill design. On the top of the 1 quart reservoir is a bleed hole that has a yellow plastic tube connected to it in a U shape. If you tip the gun, the paint won't drip out the reservoir bleed hole.
HVLP Spray Gun
High Volume Low Pressure (HVLP) guns use a low air pressure to shoot the paint. There is significantly less overspray and 90% or more of the paint lands on the vehicle. There is no cloud of paint floating in the air and hardly any paint lands anywhere except on the part being painted. Just because it is low pressure it doesn't mean that you can use a cheap air compressor. You need a compressor that can provide the volume of air at about 10 CFM and that is typically a 5 HP minimum compressor.
Notice that the air pressure is measured at the gun with an air gauge and not at the compressor and that the paint pot is on the top of the gun. It uses gravity to help move the paint. One thing that you have to be careful with is that the pot lid is on securely when you are painting awkward areas like door jams. You don't want to be shooting up and spill a pint or two of paint! I've even masked the lid on. Another thing about top pot guns is that the balance is very different from the old style guns - the gun tends to be top heavy so smaller pots are used.
Smaller pots mean that you mix a large batch of paint and keep filling the pot as you paint. It is important that you have a stable spray gun holder as it takes both hands to fill a pot. You should always strain the paint when it is poured into the paint pot. The last thing you want is your gun to start spitting while painting because a fleck of dirt or unmixed paint clogged the gun.
There's three adjustments that you can adjust on the touch-up gun: pressure, material and pattern:
The first control is the air pressure which I set at the gun. The paint instructions will state what the paint pressure should be at the gun handle. HVLP gun instructions will state something like it requires 45 psi at the gun to shoot 10 psi from the tip. While the 45 psi is the same pressure as the older high pressure guns, the actual pressure at the tip is only 10 psi. The air pressure is critical for correct atomization of the paint. You want fine even droplets at the edge of the spray pattern. You should have a regulator at the gun to control the air pressure.
The second control to set is the material knob. The material knob sets how much paint is sprayed. The rule of thumb is to screw the knob all the way in and then out by 2 1/2 turns. his is the initial starting point that manufacturers recommend. The next time, I spray, I'm going to try adjusting it this way and the method shown in the above video to see which is better. I check it by test spraying a piece of masking paper so that the paint didn't run after spraying and holding for 2 seconds. You shoot about 8"-9" from the surface. Naturally, all three adjustments interact with each other - so you may have to run through the steps several times to get the right combination!
The fan control which sets the shape of the spray pattern. It should look like a "cigar" and be even spray throughout. I set it for about 6" to 8" wide depending if I was painting tight small areas like the dash or larger areas like a body panel.
Fan out of spray pattern
Interestingly, the gun tip is at 90 degrees from what the spray will be. The gun tip can be rotated to any position and tightened.
This pattern has very poor atomization as can be seen from the large droplets. It may not have enough air pressure or there is too much material being shot. Usually if there is too much material, then the paint will run with the 2 second test. It also looks like the gun was tilted towards the top when held as the top is thicker and has more paint.
The most important step is to test your settings by spraying on a piece of cardboard or flat surface. You should be able to spray for 2 seconds without running with a fine even atomization. This should be done every time you use the gun and in between coats. There are a lot of factors that come into account when you are setting up your spray gun: paint viscosity, air temperature, air humidity, paint tip, type of paint, etc... Only adjusting the gun and testing it will let you shoot a perfect coat.
Cleaning the Gun!
The last step in using a spray gun is cleaning it. You want to immediately clean the gun before the paint dries inside. Once the paint is dry, you might as well throw away the gun as it is near impossible to clean.
The higher end guns have a throw-away pot liner and all you need to do is to clean the gun. Some people spray thinner through the gun to initially clean the insides and reduce the amount of cleaning required. Here's a step by step guide to cleaning a gun:
I've previously painted 4 cars in my lifetime, all with spraybombs (lots of them). I was very impressed with the control and the consistency I had during painting when using proper equipment and paint. I was worried about mixing the paint, spraying the paint and even cleaning up the spray guns. It was a lot easier than I thought and a lot easier than spray bombs.
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