Scott's Guitar Blog: December 9, 2006

Tone Wood Moisture Content

It doesn’t matter how beautiful the wood you have is, if it isn’t at the right moisture content when you make a guitar out of it! You’d be stunned how many builders I know don’t keep their shops properly climate controlled. Even some who do don’t check the moisture content of their wood. If wood is not dry enough when it is made into a guitar, it will shrink in the dry weather causing warping, cracks, and other problems. It is one of the most critical details to use stable wood!

I keep my shop at a relative humidity of 45-50% at all times. In theory, stored tonewood will be safe to use in this enviroment. I like to be certain however, for example, before I machine out an electric guitar body, make a neck, or an acoustic guitar soundboard, that the wood itself has a safe moisture content. I like to see my wood in the 6-8% range. I feel this is perfect for joinery, and all aspects of guitarmaking. Different species of wood however can fool you…each has its own specific gravity (lower in soft woods, higher in hard woods). Traditional pin style meters only give you a rough guess at the entry area of the pins, not the whole board.

The meter seen here is amazing. It is a pinless meter, using electromagnetic radio waves. It sends waves deep into the wood over a 1.5″X2″ area to measure the moisture content. It also has a species specific mode where you can enter the correct approximate specific gravity of the wood being measured. These numbers are a close estimate, and will vary a bit from board to board, but are close enough to trust. The piece of Koa I’m measuring in the photo will make a lovely back and top set for a ukulele. I set the specific gravity to 67 as the chart suggests, and then take a reading. It is 6%…perfect! Western red cedar for instance, has a specific gravity of 32. If you use a meter set at a standard 50 default for example, your readings from species to species could be off by 5% or more! I have bought wood from vendors who supply luthiers and seen numbers as high as 20% in wood that was supposedly dried and ready to build with. That is why this meter is so critical. A few months in a climate controlled shop will bring it right into line with my requirements for building.

This meter is a Wagner MMC 220 available from Woodcraft.com for about $299.00
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