As mentioned last month, the 2016 five-guitar project is nearly complete, the finishing process is underway. When I first started building instruments, I felt that 'finishing' was the wrong word to describe this process. Actually, I believed that it ought to be called 'starting all over again'.
The tools, equipment, processes and even the work space has to be completely different from a woodworking project. Finishing is not a process that Woody looks forward to. This is because finishing is not wood...working. Finishing requires the use of tools and materials that are unrelated to shaping wood to dimension and assembling components.
Just because finishing requires new and different skills, however, there's no reason to complain. If done in a controlled manner, finishing adds value and appeal to your work already completed.
If one has built a guitar from scratch, the labor that went into it can only be fully appreciated by another luthier, and maybe a few musicians. The other 99.999999% of the world will judge it by what they see first... the finish. That's just the reality of it.
(Note: If the text and photos don't line up, zoom in or out to uncover.)
That being said, I know several very popular guitar makers who sub out the finishing. Woody might do the same if he could find someone within 50 miles that knew how to do it. I checked into it and all I found were furniture finishing and re-finishing shops. None could produce the high-gloss lacquer finishes that are now the standard for stringed instruments.
So, a small-time luthier must acquire the tools and skills for himself. In the end there is some peace of mind to controlling the entire process... yet, that is also the challenge... control. This month I will try to explain a few of the 'necessaries'.
Understand that Woody is not a finishing expert and the descriptions below are how Woody goes about the finishing process given the budget and equipment that are available. Many of the techniques described are not recommended for production work. I will apply a finish to five guitars in the next month and that will be my 'production' for this year.
In my research to find a finishing shop that could apply and polish my completed instruments, I met a professional refinisher who had some interesting recommendations. His comment when I asked him what spray gun he recommended was, "They're all crap!" He might have been having a bad day, but the sentiment was well taken. Spray guns can malfunction for seemingly no reason.
Today there are HVLP (High-Volume, Low-Pressure) guns that deliver the finish more efficiently than siphon guns. That is, they deliver more volume (more lacquer) and require less air pressure. These are generally gravity guns_ meaning the canister is mounted on top of the gun. Gravity guns also require less air to move the finish from the canister into the air stream through the nozzle. (i.e. gravity is helping).
Another advantage with a gravity gun is greater ease in spraying at angles. It's best to keep the gun upright at 90 degrees to the work, but sometimes, that's not practical. The gun pictured is a DeVilbiss Starting Line. It is pictured as a generic HVLP. It's not expensive and probably a very good gun. I don't have one (yet).
All this being said about HVLP guns, it might surprise the reader that Woody still uses a traditional bottom-canister, siphon gun. That's because I believe that "It's better to deal with the devil you know, than the devil you don't know."
Right now I am probably in transition to an HVLP gun, but I've been using a siphon gun for 30+ years and I know how to use it to spray high volume with little over spray as well as how to control it for detail work. The gun is designed for auto body work, so I've modified it a bit and learned to control it to suit my needs. For instance, I am now using a smaller nozzle (and a larger compressor) for clear finishes. Auto paint is thicker and requires a larger nozzle. When shopping for a clear coat nozzle, 1.4 mm is about right.
The gun pictured below, and most siphon guns, requires more air (> 6cfm @ 40 psi) than HVLPs . This is important when shopping for a compressor. Since I up-sized my compressor to 8 cfm @ 40 psi, the gun has taken on a new life. With my old compressor, I often needed to modify my vocabulary to use the gun. Most of the problems were due to my compressor being too small. A lot of guys my age use a similar gun. The gun pictured below is also a DeVilbiss but from the old DeVilbiss company. Similar guns are built today but mostly off shore.
The compressor is the heartbeat of the finishing system. In choosing a compressor it's a good idea to avoid oil-lubricated machines in order to reduce the chance of fouling the tank, lines and gun with oil. In-line filters are a good idea. When shopping for a compressor, be sure to know your gun's air delivery requirement and the air delivery capabilities of the compressor. That information is a nameplate standard and in the machine specs, i.e. xx scfm at 90 psi and xx scfm at 40 psi. The smallest compressor one might use in setting up to spray guitars would have at least a 10-gallon tank and deliver at least 6 scfm at 40 psi. (scfm = standard cu. ft. per minute) Check the nameplate.
Another point to be aware of with compressors is that they are often driven by large electric motors (3-4 hp or larger). The nameplate amp rating is a good thing to check. It will be written something like 15.0/ 7.5A (see above).
The 7.5 A is the running amp requirement and the 15.0 A is the in-rush amp draw. When the compressor is first turned on, it spikes the power supply (in-rush) in order to get the motor spinning and up to speed. If the
compressor is on a normal residential 15-amp circuit it could trip the breaker every time it's turned on. It may need a dedicated circuit and require a 12-awg extension cord. Think about it.
When buying a used compressor these are just a couple of things to check. Was the tank routinely drained? Is the intake filter intact and clean? Do I have an electric circuit that I can dedicate if needed? Are the tank and spray volume adequate?
The guitars that one sees in retail music shops these days are generally finished with polyurethane (low end) or nitrocellulose lacquer (high end). Lacquer is the choice of most of the small, high-end instrument makers at present. Woody Strings uses Behlen or Mohawk instrument-grade, nitro-cellulose lacquer (or equivalent). What's "instrument-grade' lacquer? It's more flexible than furniture lacquer. That's all that I want to say about that right now.
Like most finishes, lacquer comes as a high-gloss or some grade of satin. Satins are graded according to their respective sheen (10, 20, 40, 60, 80). Number 80 sheen is Classic Instrument Lacquer clear gloss. 10 sheen is flat and 20 sheen as very low gloss matte, almost flat. 40 sheen is what Mohawk calls satin. 60 sheen is semi-gloss. I like to use 80 sheen for a full gloss. If I am going for something a little flatter, I use 60 sheen...semi gloss. It's a personal thing. (See Mohawk Finishing Products)
A gallon of instrument lacquer will cost about $40... about the same as high-grade Sherwin-Williams paint. BUT... they probably don't sell instrument-grade lacquer at your local paint shop so one has to order it and pay the freight which will be about $20. It's the same freight charge up to three gallons. Might as well buy three gallons and only pay freight charges once.
A WORD ABOUT MAINTENANCE
KEEP IT CLEAN. Spray gun operation can be frustrating. Starting out I have this advice. Keep your spray system as clean as possible (spray area, spray gun, hose, compressor, etc). This means water and air filters in line before the air reaches the gun and cleaning the gun after every use. The degree of cleaning depends on what has been sprayed, how long it will be before using the gun again, and if one intends to spray the same medium. Changing from tinted sealers or lacquers to clear top coats should be applied from an entirely different gun to ensure no surprises.
No matter how clean you keep things_ bugs happen. Be prepared to remove minor bugs immediately... before the lacquer begins to set. While the just-applied lacquer is liquid, it is gracious. Little digs and rubs can be blended with the next coat if applied immediately... i.e. while the last application is still wet.
When finished using the compressor for the day, one should always drain the tank. This allows the moisture (water) that has accumulated in the tank to drain out. Otherwise, rust forms inside the tank. Moisture in the hose can be filtered with a moisture filter in the compressed air line. Also, be sure to maintain the intake filter on the compressor. If the intake compressor filter is broken or removed, dirt and water will accumulate in the tank and will eventually end up in your hose and possibly in your finish.
THAT'S ALL FOR THIS MONTH. I'm starting two mandolins and just picking out the wood for it this week.
So, there is way more going on than I have time to write about. Did I mention my made-from-a-kit CNC machine? It works great for small, delicate projects like inlay and cutting fret slots. I'm having to learn 3 new computer programs at once but the results are pretty good so far.
Hope that you come back next month.
If you're near Richmond, VA, drop me an email:
... happy for you to stop by.