Making the Back Workboard
Learn to make a back workboard that will set the spherical shape of the back of your guitar. The backs of most quality classical and acoustic guitars are not flat, they are domed. The back of a classical guitar is typically domed to a 15′ radius. The braces on the back hold it in its domed shape. the bottoms of the braces are shaped to the 15′ radius and glued on to the back in the workboard. In order to do this correctly and preserve the shape the back workboard must have a concave surface mimicking a small section of a 15′ rasdius sphere.
The back workboard is not difficult to make. It is a simple carving jog really. The hardest part in my opinion is visualizing the shape of the surface. In order to do that you must imagine the outline of the guitar intersecting with a 15’radius sphere. If you can do that you know what the perimeter of the workboard, or outline of the guitar, will be at different heights as you move around it. The parts of the edge that are closer to the center will be higher than the ones farther away from the center. Visualizing and understanding how the shape is arrived at will help not only with creating the workboard but other aspects of the guitar building process as well. Visualization is important with any construction project.
Making it as described in the video below you will teach you valuable skills that you will need when building your guitar. You will learn to carve using a gouge and learn how to use and possibly make a curved bottom plane. If you make the effort to make the plane you will not regret it. The plane will come in handy making it will be a lesson in itself. With a little practice you should be able to make this workboard in one sitting. It should not take you more than a half a day even if you have never done it before. Check out the video below. There is a tool list at the bottom of the page.
Why Make a Back Workboard?
The back of a classical guitar is not flat is it domed. The spherical shaped surface evenly distributes tension and pressure and can provide a pleasant visual effect. A flat back would have flat braces inside and will not distribute pressure evenly. That is why you don’t see many flat bottom boats or square gas tanks.
To create the dome shaped of the back, the bottom edges of the back braces are shaped to the desired radius and glued to the back in a concave work-board. To do this you need a workboard dished to the proper radius to hold everything in the correct shape as you put together the back. The back workboard must be dished or scooped out to the desired radius. This is not difficult to do by hand if you know what you are doing. Carving out one of these work-boards is a great woodworking lesson in of itself. There is similar carving to do on the solera so this is great practice.
Applying Finish to the Workboard
When construction of the solera is completed the entire work board must have finish applied to it. Shellac is an excellent moisture barrier so begin by coating the work board with at least 3 coats of shellac. After the shellac has dried a more durable finish may be applied over it such as varnish.
I recommend also putting on a top coat finish over the shellac. Any type of hard, durable finish will do. This will give the work board some protection and also make it impervious to alcohol or shellac which may be used on the guitar while in the solera. If the solera is finished only with shellac any alcohol or shellac that accidentally ends up on the surface of the work board will mar the finish. Watch a video on how to spray a finish on your work-boards.
Tools for Creating the Back Work-board
Virtually the same tools are necessary to create the back work-board as those necessary to create the solera. If you have all the recommended tools creating these work-boards will be easier and faster. The short list of tools for making the back workboard is as follows:
Compass planes are rare. Your best bet is to make one yourself. Its an easy project that will teach you some basic woodworking. A plane making dvd and plane making kits are available in the store. The kits contain everything you need to make your plane.
I also offer a plane making class. Students leave with the bench and compass planes they create in the class.