Finishing the guitar can be a very ominous task. I know that I had struggle with getting that perfect finish for a long time before I perfected my own style.
I can tell you from experience that the quality of your finish will be governed not only by your skill level, but by the quality of equipment that you purchase.
I started out with a very inexpensive system from the automotive store and happily went on my way to try to finish my first guitar, only to find out that I had do strip the finish and start over again. I had moisture in the system and had a finish blush, which makes the lacquer have a whitish tint. Also i had fish eyes. My self-esteem was really low after that experience.
So…I decided to get equipment that was up to the task. For a spray gun, I wanted a small, easy to handle gun that would have the ultimate in adjustability and give me any spray pattern that I wanted. So I chose the Binks Model 115 and I still use that gun today. I just purchased the 8 oz. Model 810540 cup, which is just right for one spray operation. If you are going to do more than that you may want to get a larger cup.
This gun requires a compressor that is capable of producing at least 1.5 cfm at 90 psi. It uses a 1/4″ air hose. When spraying lacquer, I have had the best results with somewhere between 30 and 35 psi available at the gun, so you would set your regulator inside the booth to about 35 psi. I love the overhead trigger that you control with your index finger. It gives you the ultimate in control.
If you will be using a water-based finish, then you will need to pump up the pressure a bit to about 45 psi and for the thinner stains, try about 60 psi.
You will find the control that you have with this gun is incredible. You have a wide range of spray patterns, from narrow to wide. You can use it for fine detail work as well as spray work for the large guitar surfaces and you can even use it for applying stain or shading if you would like to spray a sunburst pattern for instance.
As far as compressors go, you should get one with at least a 20 gallon storage tank that will allow you enough time to finish the guitar without the need to let the compressor to catch up. The smaller, nail gun compressors will not work very well for these types of duties as they are designed for short bursts of air to a nail gun. It is not too important that the compressor have a built-in regulator, (but most do) as I would recommend a much better quality, and usable regulator be mounted directly on the wall inside your spray booth to allow easy access for easy access pressure settings. Also, an added benefit is to look for an oil-less motor.
Air Filtration and Regulation System:
One thing that is absolutely necessary is a moisture capture system. I would place this in-line, just before the regulator in the booth as well. This will eliminate all moisture-related finish issues. Ideally you can put in a combination regulator-filter-air trap inside the booth. This will completely trap contaminates, moisture and give you the ultimate in air pressure control. Also if you are concerned about oil entering the system, install an oil capture system as well. Go with all brass fittings on this valving and capture system if you can and skip the cheap plastic setups.
As for air piping from the compressor to the booth, you can use galvanized steel piping, copper, or rubber. I would recommend that you use galvanized steel or iron piping with iron joints. Be sure to seal all the joints as you install the pipe to eliminate leaks.
When you install your piping, run the lines slightly uphill with moisture drains installed at the low points of the pipe. Compressed air is typically heated and holds quite a bit of moisture. As the air cools in the pipe the moisture condensates and this can then be drained at the valves at the low points in the lines. Also we want to eliminate as much moisture as possible before it enters the booth.
The longer the runs from your compressor to your booth the better. This gives the air a chance to cool down and you can address your moisture issues much easier. If you can manage a 40 to 50 run of iron pipe, I would recommend that.
Next get a quick-disconnet coil air hose that will allow you the most freedom without the hassle of a tangled air hose.