The Auto Painting Tips Newsletter

With Chris Curwen & Expert Auto Painter - Dave Gage (Car Cosmetics)

February 13th, 2008 - Issue 40

All About Auto Paint Spray Guns - Paint Cups, Air Valves,
Why Quality Over Economy, the Importance of Seeking Professional Advice and heaps more.

It is recognized across the automotive painting industry that Sata, Sharpe and DeVilbiss are the three most popular brands of automotive spray paint guns.

Any novice shouldn't have any problems producing great results using equipment from any one of these name-brand manufacturers. You wouldn't see Tiger Woods teeing off using a $20 driver now would you!

For a full range of the various spray paint guns and all of their accessories, take a trip to your nearest auto body paint and supply store. Prices will start at around $80 with the overall cost depending upon the brand and level of precision quality.

Paint Cups

The paint cups are usually extra and will generally cost you $25-$40.

Air Valves

In addition to paint guns, you can purchase air valves that attach to spray guns in-line with their air supply. The purpose of these valves is to help you fine-tune the air pressure at the gun to perfect your paint spray patterns. We'll talk more about how to perfect your paint spray pattern a little later.

The Number One Factor You Must Consider When
Purchasing a Spray Paint Gun is...

Answer: Spray Gun Quality.

It's our advice to save up the extra money required to buy a top-of-the-line model than to settle for a middle-line unfamiliar import.

Why go for quality rather than economy?

The problems with cutting corners and buying a cheap paint gun relate to inadequate spray patterns and trouble in finding replacement parts.

ALWAYS opt for durable quality instead of make-do availability.

Going back to my earlier example, you wouldn't feel too confident entering a golf competition using a set of golf clubs you borrowed off Uncle Bob who bought them 25 years earlier...of course not, you'd go to a proper golf focussed outlet.

The materials that modern day golf clubs are made from are cutting edge designed purely for one thing and one thing only...to enable the user to get as much distance and/or accuracy from using them.

It's the same with modern high quality paint spray guns, the components they are made from are the result of thousands of hours of painful research and development, hundreds of thousands to fund that research and development.

The end result is a paint spray gun that does exactly what it was design to do...provide optimum results.

Seek Professional Advice before you buy

You need to take your paint gun purchase seriously and therefore buy from an automotive paint and supply store, the specialised knowledge available to you at these places will be everything you will need.

By being in direct contact with a knowledgeable salesperson who has firsthand experience using the spray gun you are considering buying has some advantages:

You see, product literature may suggest a particular setting for inlet air pressure; while real-world experience can assure you that an alternative inlet air pressure may be necessary.

If you do not have access to this firsthand knowledge, your brand-new spray gun may NEVER operate as well as intended.

Inlet air pressure settings are CRITICAL with HVLP spray guns, so it will be worthwhile to ask someone who knows for their recommendations, rather than relying solely on product literature.

Remember, what works and what works best may not be the same.

With conventional spray guns a typical air pressure of 60 psi or more is required. This quite high pressure blasts paint onto the surface with such force that over 65% of the material is lost due to overspray.

Additionally, the high air pressure is more likely to disturb existing dirt and debris and allow it to fall onto fresh paint causing a less than perfect finish.

High-Volume Low-Pressure Spray Paint Guns

A more practical solution was the development of HVLP spray guns.

How HVLP works is by increasing the volume of paint that can uniformly pass through the spray gun's ports and nozzle, so that a relatively low pressure is all that is needed to propel the paint material out.

The end result is that more paint adheres to auto surfaces and much less is wasted through overspray via paint particles bouncing off surfaces at high pressure.

And the benefits of this?

Well, with the price of paint material alone being at what it is, the purchase of a HVLP spray gun will certainly pay for itself in a couple of repaint jobs, if not the first one.

Not only will you save paint material with a HVLP spray gun, you will see a great reduction in the amount of overspray, which should be of major importance to any part-time auto painter who is working in his/her residential garage or workshop.

It has been recommended for HVLP spray guns to use an air pressure of 10 psi at the tip of the spray gun.

This is not to be confused with the air pressure at the inlet of the spray gun where the hose connects. It depends on the design of the spray gun but the inlet pressure may sometimes be near 60 psi to obtain the suggested tip pressure.

There are 4 main types of spray paint guns. Those are...

	SIPHON FEED - A siphon feed gun's paint cup is mounted below the air nozzle. This design requires more air pressure to siphon the paint material up and out of the cup. With a non-HVLP siphon feed spray gun, approximately 75% of the paint material ends up as overspray.
	GRAVITY FEED - A gravity feed spray gun has the paint cup mounted above the air nozzle. This allows gravity to do the work for some of the air pressure, allowing for the use of a lower inlet air pressure. However, on a non-HVLP spray gun, this will result in approximately 65% of the paint material ending up as overspray.
	PRODUCTION GUN - If your painting is going to be limited to large body panels, such as doors, fenders and hoods, a full-size production gun will suit your needs. Commonly having a one-quart paint cup, this gun can spray a fair amount of material before you need to refill.
	DETAIL GUN - The difference here is manoeuvrability. Detail guns are perfect for intricate painting jobs, like small touch-ups requiring fine spray patterns and door jamb painting.

Paint spray gun control and test patterns

Paint companies recommend specific spray gun setups for applying their products with. This would include a specific fluid tip and air cap that should be used with the particular paint product that would be available from the dealer of the spray gun.

This is another reason why you should purchase your spray gun from a paint supply store instead of from a tool store that sells a variety of tools without servicing any of them.

These settings are available from information sheets and application guidelines or from your auto paint supply store worker who may have firsthand success using a particular spray paint gun setup.

Most full-size production spray paint guns have two control knobs located on the upper rear section of the spray gun housing. These control the volume of paint that exits the nozzle and the airflow or fan spray.

Material control is usually adjusted by the knob that is in-line with the air nozzle, whilst the airflow is adjusted by the remaining knob.

Refer to the literature included with your spray gun or ask your paint spray gun supplier if you have any questions regarding adjusting or cleaning your spray gun.

This is yet another reason for purchasing a spray gun from an auto body paint and supply store instead of from a general, discount store. A properly adjusted spray gun will give you professional results and will last a very long time if you clean and maintain it correctly.

Practice makes perfect

Now, you are going to have to practice in order to learn how to make proper spray patterns and volume, this is important.

Various paint products and their reduction ratios will spray differently, especially with different recommended air pressures, so get hold of an old panel and use it to perfect your skills.

Many painters keep test panels in their spray painting area or they use sheets of wide masking paper taped to a wall, either will provide you with an excellent medium in which to practice and/or test on.

Our advice is to spray paint onto the test panel and then make adjustments to your gun in order to get the right pattern and volume. Never start the actual painting until you are sure you have the correct setting on your paint gun.

Occasionally, during your paint job, you may notice a defect in your gun's fan pattern. To check it, turn to your test panel and shoot a clean section with a blast of paint. If it doesn't look right, check the controls and the air pressure.

If the pattern is still flawed disconnect the paint gun from the supply hose and clean it thoroughly. The chances are that a small port or passageway has become clogged and must be cleaned before you can continue spraying paint.

As you move around your vehicle the surfaces that require paint are never the same for long and at times become more confined or difficult to reach, as on some front end sections.

In these instances, you must reduce the air pressure or change the fan spray to hit the smaller areas. You can make these adjustments again by practicing on your test panel.

The benefits of using a holding rack

Finally, holding racks are very useful when painting separate sections of dismantled bodywork as shown in How to Paint a Car - The System. These racks are designed to tilt and adjust for the part that needs to be painted.

They are commonly used in auto body shops but possibly too much of an investment for the average person painting their first vehicle. If you get lucky enough to find a second-hand rack still in great condition, it could turn out to be a very useful tool to add to your collection.

Check with your auto paint supply store; they may be able to point you in the right direction for getting hold of one.

If you can't get hold of a rack then you could try making your own, failing that make the most out of lying down or hanging up the parts to be painted.

You will need to place them so that you can comfortably access all of the part(s) for painting. This won't always be possible but do what you can to make your life easier.

After you feel you have painted all of the surfaces, take a second look at it from various angles to make sure you haven't missed anything.