Using Dry Wood for Tapping-Instrument Stability

– by Traktor Topaz

Something most of us musicians don’t often think about is … wood and moisture content.

However, the stability of your instrument can be adversely affected if the instrument is made without proper (and sometimes prolonged) drying of the wood. That is, if the natural moisture content of the live wood has not evaporated out of the cut wood, and come to equilibrium with the surrounding air, then there will be further movement — inside the wood of the instrument — even as you’re trying to play it.

• In some cases, the neck can change shape a little. Usually this is correctable using only the truss rod, assuming that the neck has been made of multiple strips of wood (which if done properly will eliminate side to side warping).
• In other cases, the ends of the frets may protrude. The metal frets haven’t become longer; the wood has become less wide, as it gave up some mass from water vapor.
• Of course, the *primary* job of an instrument finish is to slow down the movement of water vapor into and out of the wood. Even properly-prepared wood may have some changes later, if you play one night in the Phoenix desert and the next day in the coast city of Seattle. Beauty is nice, but the primary function of instrument finish is to slow down any later loss or gain of water vapor.

TALKING ON TAPPISTRY FORUM

On the Tappistry Forum (http://tappistry.org/forum), a member named Julian recently reported on a home-building project because he is building his own tapping instrument.

He commented that other tasks had taken him away from his building project, and when he returned two months later, the (unfinished) instrument had frets protruding from either side of the fretboard.

He commented that he should have got finish applied to the instrument earlier.

However, if the wood shrank away from the fretends, then although that shrinkage would be accelerated by having no finish on it — he ran the much more serious risk of “checking” meaning the wood cracks open from the end grain end — and if the wood shrank, it quite possibly means that he may have been working with wood that was not fully dried.

There are premium woods that have been ‘air dried’, sometimes for year. In a violin bow factory that I visited in China, they had an entire building about the size of a two car garage, filled with thin strips of wood stacked in opposite directions, with airspace around all of them.

They built bows from the wood on the south end, and the new wood they bought was stacked the same way on the north end, and they had more than a years worth of wood stacked like that, so by the time they got to a new batch of wood, it had been air drying for over a year.

Most wood you get nowadays is kiln-dried. Now for many purposes, that may be fine, but it does mean that the wood has been dried using heat, and this is a “quick” process. As you can imagine, it actually produces wood dry on the outside, but not so dry on the inside. And therefore it continues to dry for quite some time.

And that means it continues to shrink, for all wood shrinks as it gives up the mass of the water content.

KILN-DRIED VERSUS AIR-DRIED

So if homebuilding a musical instrument, always be sure you’re getting at *least* kiln dried wood (not green wood), and then paint the end grain with paint, or latex, or parafin or something that seals the end grain to prevent “checking” (cracks), and then stack it properly (“stickering”) so that it’s not bending under gravity, but has air space around it, and then let it dry for a time.

You can of course buy green wood, from a mill, and you can get good quality and pricing; however, be prepared to buy a lot, and have a lot of storage space and lots and lots of time for the drying process.

Here at Mobius Megatar, we have most of this outsourced, so I don’t have to work with it any more, and there are many guitar builders who can give the formulas better than I, but the general rule of thumb is that the common formula (for green wood) is a year per inch of thickness, plus a year.

I suspect that’s excessive.

For kiln-dried, it will be far less, but I’ve never heard an exact formula. Of course if you have large pieces that will be made smaller, best to make them smaller first, then paint the ends, and then let them dry. Because smaller pieces can more easily give up their water vapor, and therefore come to stability (being dried out) faster.

OTHER THINGS TO CONSIDER

Naturally, all this process is an interplay that also involves the humidity in your location, your shop, and the wood-storage area. In a perfect world these three would all have the same (fairly low) humidity.

You can get a tool that shows both temperature and humidity called a Thermo Hygrometer. This is handy for any spraybooth, but it’s also good to get an idea of your shop and storage humidity through the year.

You can also get a tool to measure the ‘wetness’ of wood. A cheap one has two prongs, and a more expensive one (about $300, if I recall) uses induction. Each has to be calibrated to the type of wood, as they’re correlating resistance or inductance that can be measured easily with the water content, which varies by species and which I think can only be measured precisely by burning up the wood. (Really not recommended for your guitar building!)

But I think our Julian may have lucked out. His wood became air dried, and it didn’t crack.

That’s lucky.

GUIDELINES FOR TAKING CARE OF YOUR INSTRUMENT

Here we’ll take our cues from acoustic-guitar builders, and they seem to agree that a relative humidity of 45%-55% is best, and that 40%-70% is generally safe.

Now if you grew up in a cold climate, you may just naturally think that dry and cracked lips are just a normal part of wintertime. But actually, that’s a symptom that the humidity is too low for your skin.

And … that’s too low for your guitar as well. Are solid-body guitars as sensitive as acoustic guitars? I’m speculating that it may not be as critical, however a good acoustic guitar can be a *lifetime* investment if cared for, and I see no reason that a good electric solid body shouldn’t outlast an acoustic, if you care for it.

So how do you care for it? Of course you could buy a Radio Shack hygrometer. (Not as fancy as the professional one in our spraybooth, but should be more than adequate for the purpose.) You could also invest in humidity-indicator strips. This would be a cheap alternative to getting a hygrometer, and would still be a scientific way to protect your guitars.

If your room(s) are too dry, then you’d be wise to cease storing your guitar on a stand or out in the open. Instead, put it inside a case. You can *easily* control humidity inside the small area of a case.

Then give your guitar some moisture in the air.

For example, dampen a cloth, place it in a baggie, then punch a couple of teeny-tiny holes, and store it in the case with your guitar.

Symptoms of too-dry wood may include: some neck shrinkage and fret ends feel sharp, intonation can go off, action can rise, and fret buzz can increase.

Patrick, our Shop Foreman, once had an acoustic guitar stored too long in too-low humidity, and it became too dry, and developed a kind of hump where neck meets body. A bit of water vapor from the baggie trick fixed it easily.

But you don’t have to wait for trouble to show up. A rough rule of thumb is that, if the human is comfortable, then the guitar is comfortable. (Just don’t think that dry, chapped lips are comfortable, tough guy!)

BUYING AN INSTRUMENT?

Buying an instrument, or having one made?

Want to make sure you’re getting properly cured wood?

Then … know your wood … or know your builder!