DIY Network

Handmade Guitar, Part 3: Top Bracing and Tone Bars From "Handmade Music" episode DHMM-101

Lynn Dudenbostel places the bracing and tone bars on underside of the guitar top. Luthier's refer to this critical step in the guitar-making process as "giving voice" to the guitar.

In this segment, bracing and tone bars are added to the guitar's top and back. These additions, located ultimately inside the guitar, impact the sound of the instrument more than any other step in the process of guitar-making. Luthier's refer to this most critical step in the guitar-making process as "giving voice" to the guitar. It provides much of the beautiful and nuanced tone of an expertly crafted guitar.

Materials:

Spruce stock
Plans for guitar-top bracing
Sharp chisels
Finger planes
Sandpaper
Caliper
Straight-edge
Carpenter's pencil
Wood glue
Hot hide-glue
Clamps

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	Figure A
	Figure B
	Figure C
	Figure D
	Figure E

Top Bracing and Tone Bars

Tone bars and bracing provide both acoustic and structural support. Without them, a flat-topped guitar like the one built in this series could never transmit the beautiful sounds for which they've become known. Since the steel strings of the guitar create tension between the neck and body, the bracing provides very necessary structural reinforcement. When it comes to location for these critical elements, nothing is left to chance. After years of research and experimentation, master luthier Lynn Dudenbostel has developed exacting standards for placement.

• Following a plan diagram (figure A), he lays out a pattern on the underside of the guitar top. Then he cuts spruce into braces that will fit on the outline he has drawn.

• First, Lynn cuts four finger braces -- quarter-inch strips that primarily provide structural support for the top. He attaches these braces using ordinary wood glue and clamps (figure B).

• For the braces that serve acoustic purposes, he uses specialized hide glue. "Hot hide-glue, " says Dudenbostel, "is a traditional glue and offers very good strength and very high resistance to heat, unlike some of the modern glues. I use it in almost all applications where sound is very important. In gluing the braces to the top of the instrument (figure C) and the center-seam of the top, I use hide glue. The trouble with working with hide glue is working with it in a normal room temperature. It's cooked at about 140 degrees. Once it drops below about 90 degrees, it begins to gel. So when you have a large area that you need to glue, you have to work very fast.

• Before adding the rest of the bracing, Lynn carves the finger braces and tone bars using a very sharp chisel. The finger braces are carved down and tapered extremely thin as they reach their ends (figure D), but have a high peak in their middle. The structure of these braces is somewhat analogous to a suspension bridge, with wood removed where the stress is lower, and left intact where the stress is higher.

• With the finger braces shaped to a perfect dimension, Lynn moves on to the tone bars. The profile of these elements is meticulously trimmed and scalloped to exact shapes and dimensions (figure E). To do this, he uses finger planes, chisels, calipers and sandpaper. Lynn suggests studying the tone bars on an old, authentic Martin guitar to determine the shapes, or going by the dimensions of plans that can be purchased from luthier-supply shops.
  
  
• Once the tone bars are done, Lynn adds the X-bracing to the guitar. The X-braces (figures F and G) are key to the sound of the guitar. They are placed in keeping with the positioning on vintage Martins, attached using hide glue and held securely with clamps as the glue dries.

  Figure F

  Figure G

  
  

  Figure H

  
  
• Using hide-glue, Lynn attaches the traverse brace just above sound hole (figure H), clamps it in position and allows the glue to dry.

• Lynn also adds a plate to support the bridge that will later be glued on top. The plate is cut to fit just beneath the X-bracing, below the sound hole.

• Once the glue has dried, the clamps are removed. Lynn then tapers the ends of the X-braces using a block plane and chisel, essentially creating a "ramp" from the top down to the edge on each leg of the brace. The braces are trimmed and tapered to specific dimensions required for vintage guitars. Using a chisel, Lynn also sculpts a diamond shape into the intersection of the X-braces. He also shapes the traverse brace with a block plane, this time removing much less wood.

• Finally, a few smaller structural supports are added around the sound hole.
  

  Figure I

  
  

RESOURCES :

Kentucky Thunder
For more information on the band that appeared in DIY's Handmade Music, Kentucky Thunder -- and to hear streaming audio and download samples of their music -- visit the website for Skaggs Family Records, www.skaggsfamilyrecords.com.

GUESTS :

Lynn Dudenbostel, Luthier
Dudenbostel Stringed Instruments
Knoxville, TN

John Arnold, Luthier
Newport, TN

Ted Davis, Luthier
Loudon, TN