In our previous blog, we surveyed the various species and shapes of kerfing available and described their attributes. In this blog, we will look at some of the design considerations that might move you to choose one type over another.
Wood Movement—No matter how good your glue and your joinery is, there is no accounting for the small movements that woods make as time and environment have their effect on them. So, in order to minimize these effects, luthiers often avoid gluing two species together that vary much in density or composition. With this in mind, one might choose to use a Spruce kerfing with a Spruce soundboard, thinking that the hardwood sides would be less prone to developing a crack than the Spruce would be. Similarly, you would use Mahogany (a hardwood) for the back kerfing, were the back and sides (hardwoods) are joined.
The Rigid Rim Principle—Many modern luthiers have embraced the idea that the soundboard is going to vibrate more freely and more vigorously if it is attached to a rim (the sides) that will not absorb vibration. For this reason, many have taken to using laminated woods for their sides. This in itself should provide adequate rigidity, but it could be increased by using a hardwood kerfing and/or a beefier kerfing—such as the reverse kerfing profile we sell.
Weight—Using a lightweight soundboard is a choice that acknowledges that lighter weight material is better able to carry vibrations and that higher weight does not. With regard to this consideration, some select their brace, bridge, and soundboard material for the lightest weight (in addition to other attributes, of course). Others extend it to include the back and the kerfing and even the neck material.