Design of a classical guitar - by Bert Eendebak

10 The sides

From the discussion on the design of the top and the back the following starting points for the sides can be derived:

  • In the upper part the side should be rigid, giving no allowance to movement in any direction and an inflexible connection to the back
  • In the lower part the side itself should be rigid too, but the connection with the top and to a lesser extent with the back should be flexible in a sense that the edge is allowed to twist

For the construction of the guitar the pre-cut sides have to be bowed with the aid of an iron steam pipe or the use of a bending mold after pre heating the sides. In order to facilitate the bending process, the sides have to be thinned before bending, to a thickness of not more than 2 to 2.5 mm, depending on the wood and may be on the skill of the builder. This means for a rose wood side an overall thickness of less than 2.5 mm. Because we see the sides as a rigid part of the frame construction we could decide to start with a thickness of ~ 2.5 mm for the upper bout, ~ 2 mm for the lower bout and somewhat less in the vicinity of the glue edge of the lower bout. For brittle species like Santos or Australian blackwood it is not a bad idea to thin the sides some tenth of a mm extra at those locations the sides will be curved the most.

Image: Mould for the sides

Mould for the sides

But again, as was the case with the top and the back, we will improve the strength if we add some reinforcement bars, perpendicular to the grain of the sides, allowing for an extra thinning of the side in that region. The positions for those bars are indicated where the sides are extra vulnerable, e.g. the places which maximum curve and strain. To reflect the starting point of a flexible connection to the top these bars will not be connected to the top and have a length of 7 to 8 cm.

The tail block

From the foregoing discussions on the top, back and sides the starting points for the tail block are more or less obvious:

  • Start with a rigid piece of wood, strong enough to act as an inflexible, unmovable connection between the two sides.
  • Bevel the tail block to the width of the linings to free the top as much as possible
  • Do the same for the back side
  • The grain of the tail block may be parallel or perpendicular to the grain of the sides. Most in use and satisfying is to have the grain horizontally, so parallel with the soundboard and back. A good alternative is to have the grain of the end block vertically and use an epoxy as glue (used in the construction of the EB-guitars).

Another approach is to make the tail block out of two pieces of wood (with their grain perpendicular to each other) glued together.

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