bracing on the old, cracked spruce top

Since my kit’s guitar top died the death of a thousand dry climates I have to re-create the top piece (I’ve already mentioned that, I know).  But as I was studying up on the bracing I kept running into the arc that is on the bottom of the X-brace.  I kept wondering, “But do I need a radiased dish to place the top into?”  And the answer?  No.  The reason is this: the bracing material is flexible and as the luthier shapes the pieces to the brace template the slight curve will be small enough [12' to 30' radius] that the go bar deck [which is another topic for discussion] will press the flexible braces down to the flat top and when the go-bars are removed the slight curvature of the braces will be picked up by the whole top.  This creates tension for resonance as well as creating a shape that (as I understand it) will direct the sound internal to the acoustic guitar through the sound hole.

Bracing is amazing to me from an engineering perspective.  My dad was a civil engineer (now a pastor, the past tense is not to indicate his passing) and so I grew up with some moderate exposure to things like structural engineering and since we lived in Nevada and California earthquakes were part of that discussion.  The whole point of bracing is to keep the wood in tact as it handles the abuses thrown at the guitar body parts.  This isn’t a surprise, but it’s important to recognize it’s job is to handle vibration and keep it down.  Except that the top and back make more awesome sounds when the (right) vibration is up!  So, bracing is rather interesting because the patterns that are out there help structurally, but do impact tone and resonance.  I’m not an expert on bracing yet, but I do hope to become one.

Gnarled Wood

I’m certain that more knowledge exists all over the Internet and that I’ll be editing this post over time, but I wanted to jot down some ideas about wood.  The first thing I want to talk about is the Janka Hardness Test.  This test, which you can read some rather nerdy bits about on Wikipedia if you’d like, tests how many foot-pounds of pressure a species of wood requires to insert a 0.444″ steel ball into the block half way the ball’s diameter (0.222″ inches).  While this test was developed for non-luthier related purposes, it clearly has a use in many wood-related projects.  For example, balsa wood has a Janka hardness value of 90 while redheart has a hardness of about 1,130.  You’d be wise to avoid creating anything instrument related  out of balsa.  I’m going to experiment with redheart  as a bridge material, but when it comes to the actual wood for the saddle to fit into almost all examples are made out of much harder woods such as ebony or even maple.  This leads me to think I may need to laminate the redheart I have with some ebony to create a solid platform for the saddle to handle the string tension appropriately.  Here’s one example from lumberjocks by Randy Bretz [click on the image with 3 bridges].

I’m much more enamored with the grain and colors of wood than some of the other qualities of the woods right now.  This is a bit of a confession in contrast to being purely scientific about things.  If Spruce has the best tonal qualities, but everybody has a spruce guitar, then I’m less interested in it.  The art part of wood working and luthery is definitely more exciting to me.  Speaking of which the tailpiece and bridge on this Rick Toone guitar is phenominal!  It isn’t wood, sure, but the design is so cool I have to link to it anyway  It does however, because of the sound hole being at the bottom of the guitar, show off the wood used.

I need to learn so much more about wood, but at least for now I’m learning about wood’s properties, and I figure that experimenting (even if it ends up showing off some failures) will be good for me to learn and grow.  I’ll post my findings as I do the research.