Hello Woody friends. Here's an interesting fact. This website is getting more than 600 visits each month. I find that amazing. When I started building guitars (~1976) there were probably less than 100 small-shop guitar makers in America.
Recently, I've been considering setting up a blog to address questions, answers and new ideas. Then, however, I would be spending more time talking about guitars than actually building guitars. Besides, there are many luthier discussion blogs on line. Just Google "Luthier Discussion Forum". Otherwise, to reach Woody__ Woody@WoodyStrings.com
I am now winding up a one-year project at Woody Strings. It has taken a year for me to finish my "5-guitar" project. When I started I thought that it would take about 8 months to build 5 guitars. Then life got in the way. For one thing, I realized that I need a finishing shop that is free standing and not connected to the ventilation of the house that my family lives in. So, I took a couple of months out to build the "Wood Shed" which is not telling the whole story but, here it is.
(Note: If the text and photos don't line up, zoom in or out to uncover.)
To build a guitar in a small shop (i.e., by hand) there is no substitute for manual effort. It's as Thomas Edison said, "...1% inspiration and 99% perspiration." Edison and I are of the mechanical age where hard work meant perspiration. Today, hard work might mean long hours sitting in front of a computer screen.
Along those lines, today I will spend some time putting in conduit to the Wood Shed. That's so I can run CAT 6 cable to the CNC machine that lives out there. Next year I hope that some parts and inlays can be designed in-house and routinely cut to dimension on the CNC (Computer Numeric Control).
CNC wood cutting first requires a drawing in AutoCAD (something Woody, a mechanical engineer, must re-learn). The (.dwg) drawing file produced in AutoCAD is then converted to a machine-language file (.dxf or .stl) that actually directs the path of the CNC router. It's all very interesting but, in a way, the opposite of hand-tooled woodcraft. All the woodcraft is done in your head and a robot actually cuts out the parts. Woody is completely OK with automated processes if the finished guitar is a better musical instrument.
More on the CNC project later.
Finishing the Guitar
There are at least a half dozen steps to complete after the guitar is assembled. These steps are necessary to make the instrument ready to be sprayed (or brushed) with vinyl sealer and nitrocellulose lacquer.
During the construction process, the guitar is kept as far from damage and dirt as possible. In a small shop it still gets dirty and occasionally dinged as it nears completion. A first step in the finishing process, therefore, is the cleaning and final sanding of the entire instrument. This shouldn't take more than a couple of hours if one has been careful along the way. There are always tooling marks and smudges that need to be removed.
To clean the guitar of surface oils, acetone is reliable and effective... and leaves no residue or smell. A caution is needed, however, with the use of acetone on rosewood. Acetone will draw the oils out of rosewood which will stain any lighter colored wood (like maple bindings or perflings). This staining is one of the reasons that most guitars have plastic bindings these days. Woody, of course, finds wood bindings to be attractive. So, I make the effort to keep the bindings clean and use no wood stains of any kind on the guitar if possible.
Final shaping of the neck is also done at this point, if it is needed. Woody likes to string up each guitar and play it before spraying the first coats of sanding sealer. This way I know the feel of the neck in the musician's hand... before nothing can be done about it.
The last step before spraying is the masking of the parts that are not to receive lacquer. This includes the fingerboard, the bridge and the sound hole. We touched on this last month. When masking the fingerboard, be sure to snug the masking tape tight around the end of each fret. Otherwise, there will be a little mess of lacquer that creeps under the tape and onto the ebony or rosewood at both ends of the fret.
The five guitars shown below are ready for spray except for the masking of the sound hole from the inside to keep lacquer out of the acoustic box. Usually, I stuff rumpled newspaper inside the box and that presses a circular cardboard cut out up against the sound hole from the inside.
Purpose of the Finish and Choices
The last skill that must be mastered to complete the guitar is that of applying a protective finish to the exterior of the guitar (except for the bridge and the fretboard, of course). The type and thickness of the finish is a matter of personal choice, however, instrument-grade, nitrocellulose lacquer is sold specifically for this purpose.
A few words of explanation: Polyurethane is used on many guitars sold in retail stores. Of course, plywood guitars are also sold in retail stores and online and these, almost invariably, have polyurethane finishes. Polyurethane is not suitable for a solid-wood guitar, in my opinion. It's just too hard and inflexible. If one is buying a plywood guitar the buyer is probably more interested in cost than in guitar resonance. Hand-made and high-quality manufactured guitars deserve much better.
Instrument grade lacquer is made to be flexible and that is what large, resonating, solid-wood surfaces (like guitar tops) need. Polyurethane is hard...very hard... and, for one thing, impossible to repair. So, one can imagine what it does to the flexibility of the guitar top.
Guitars are large, lap instruments and difficult to keep from bumping and scratching occasionally. Polyurethane is good for the rough lifestyle that almost all guitars must endure. As with furniture, mechanical protection of the wood is the primary purpose of the finish.
Resistance to change in humidity is not the purpose of the finish. No finish is applied to the inside of the guitar (or violin, or piano... or a chest of draws, etc.). The finish protects the instrument from liquids and ambient moisture only on the external surfaces of the guitar. This is a good thing for a number of reasons which we do not need to discuss here.
The finish should protect the exterior of the instrument from damage while minimizing the dampening effect on the transfer of sound vibrations through the wood. For a guitar, minimum sound dampening means using instrument-grade lacquer.
Unlike polyurethane, lacquer finishes continue to shrink over the life of the instrument and this is one reason why guitar tone improves as it ages. My experience is that the tone of an acoustic guitar does not fully 'mature' until both the wood and the finish of the instrument are 10-15 years old. I will never advise refinishing an old guitar. Restoring the day-it-was-built look will come at the loss of sound quality. Of course, this is completely contrary to Woody's perspective that a guitar is to be played and enjoyed for its sound, and admired as a museum piece... well... later.
In the Southeastern US the ambient relative humidity is a serious factor in the application of volatile finishes like lacquer. Ambient moisture in the air can become entrained in the spray and carried into the applied lacquer. Indirectly, this causes blushing, which is a fog trapped in the finish that is trapped in the applied finish if it reaches the dew point as it cures. It's the same as fog that one sees in the morning after a cool night following a very warm day. The moisture in the air at sundown is released into the air at the temperature falls below the dew point. Thus, the benefit of temperature and humidity controlled spray rooms.
Woody does not spray when the relative humidity (RH) is above 55%. That means that in the summer, when the temperature is right for spray application, the RH conditions are not. In Richmond, VA the best month for spraying lacquer is April. That's when, on average, both the temperature and RH conditions are right. At other times of year, like right now (October) one must wait for a day when the ambient conditions allow trouble-free spraying.
Large manufacturers have the benefit of climate-controlled, well-ventilated finishing booths and curing rooms. Most of us little guys do not. There are two major challenges, therefore, in a small shop... humidity and temperature control, as well as safe and effective ventilation.
Spraying lacquer creates immediate safety challenges in the ventilation of overspray and fumes. Lacquer is extremely volatile and any spark as from a compressor or fan motor, or fluorescent lights in the spray area can trigger a fire or explosion. I do not mention this casually or as an incidental. Safety precautions MUST be taken to avoid what could be catastrophy when spraying volatile liquids like lacquer. If not properly ventilated, lacquer overspray will accumulate on the walls and ceiling of the spray area and this is like painting the walls with nitro-glycerin. Small-shop luthiers have three choices:
Build a dedicated space and ventilation system for finishing
Brush on finishes in a space with a dedicated ventilation system
Woody has used the last two options successfully and the results have been acceptable; albeit with considerable effort. The Wood Shed mentioned above was built primarily to move all finishing procedures out of the Wood Shop... which is attached to my house and on the same ventilation system. Safety first.
Setting up to Spray
One will notice that the first challenge to spraying finish on a completely assembled guitar is that, unlike furniture, the entire exterior of the guitar receives finish. There is no 'bottom' that can rest on the floor while spraying the remainder of the instrument. The entire guitar must be within the line of sight of the spray gun at some point. This means that the guitar must, somehow, be suspended and still be capable of being manipulated while spraying. Hmmm...
The solution that I have found is truly effective and simple. Pictured below are various snapshots of a guitar suspended from the ceiling of the Wood Shed. One of the photos shows that the guitar is suspended from a board that is attached to lazy-susan hardware in the ceiling. Thus, the guitar can be rotated laterally and sprayed on both the treble side and the bass side without the luthier changing position.
Woody starts spraying with the guitar top facing up. Then, after spraying the top but not the neck, the guitar can be rotated vertically and the back, sides and neck can be sprayed.
Special (but not sophisticated) hangers have been fashioned to allow 360 degree rotation along the axis of the guitar. The peghead must have wire hangers attached to both ends of the dowels through the peghead. This allows switching from 'top-up' to the 'top-down' spraying by holding the guitar by the neck to rotate. At the same time, the butt end hanger flips 180 degrees.
Rotating from bass-side to the treble-side spraying is accomplished with the lazy susan. This method of suspending and controlling the guitar while spraying is incredibly simple and low tech... just the way Woody likes it.
Hope to see you next month and show off some shine on these guitars. While waiting for temperature and humidity to be right, I'll be working on my AutoCAD and CNC testing. That should be interesting.
Keep music in your life.
Joe Lenzi, dba Woody Strings
The Wood Shed