Solera

Acoustic guitar building / Chapter 1 : Before starting / Solera

Plan

Reduction of a solera plan (guitar : Torres)

Below, the pdf file, in A0 format.

A lot of varieties are possible depending on the building method you'll choose (sides assembly using the mold or not, use of spool clamps or not, etc.)

The curve for the soundboard may vary from 2 to 5 millimeters at the deepest point, behind the bridge position.

Media:Plan-solera-A0-ech1-2.pdf‎

Materials

• big board(s) of MDF or plywood (530*900), minimum thickness of 18mm.

Note : It is possible to make a solera that can be used also as a go bar deck that permits to glue easily the braces. In this case, it should be reinforced by adding another board to get a minimum thickness of 40 millimeters.

Building steps

1. Draw the center line (axis of simmetry)
2. Draw the guitar shape using the plantilla
3. Draw the outer line of the solera
4. Cut the external shape of the solera
5. Drill holes equally spaced along the edges (5cm between each hole and 5mm away from the exterior shape of the guitar)
6. Cut the grooves along the edges (if you've planed to use spool clamps and support blocks as Courtnall does for de sides and back assembly). Another method is to use side support molds, fixed on each side of the solera and closely following the definitive shape of the sides. The sides are then pressed against the soundboard with cam clamps. We will use here a mixing method were the side molds will be drilled to permit us to use both molds and spool clamps.
7. If you planned to use strips of rubber to glue the back on the body of the guitar, drill holes along the edge of the solera in order to insert some 12 mm diameter pegs into them.
8. If you decided to use side molds, drill some holes in order to permit to fix them onto the solera.
9. If you want a solera to be convertible into a go bar deck, drill the necessary holes.
10. if you decided to use side molds, drill the holes that are necessary for their fixation.
11. Draw the curve shape with some concentric smaller shapes inside.
12. Use a router to dig the curve, folowing the steps of the stair.
13. Finish the curve to have something regular with a sand block.
14. Drill the center hole at the rosette location.
15. Draw with precision the lines of reference.
16. Varnish.

Advices

How to draw easily the external shape

You can help yourself with a Ø15cm disc with a hole in the middle :

drawing of the extrernal shape

Making the center curve for the soundboard

center curve of the solera

• The easiest way to regularly make the curve of the solera consists in making some "stairs steps". Draw the shape of the curve then draw similar concentric shapes inside until you reach the deeper point (at the bridge position of the soundboard).

To make it easily and precisely, and symmetrically, you can use half-patterns made of bristol boards.

solera's curve drawing

Voici un fichier dxf avec les gabarits pour creuser précisément la solera (gabarits réalisés en fonction du plan de la solera donné ci-dessus).

fichier dxf des demi-gabarits permettant de réaliser le creux de la solera

Le fichier pdf correspondant ː

Media:Plan-gabarits-creux-solera.pdf

Using a router, "dig" the "steps" between the lines.

In order to maintain the router in a flat position, you can help yourself with a piece of MDF of plywood, drilled in its center :

One step of the stair being done

One step of the stair being done

Finally, smooth the curve with a scraper and then, with some sandpaper on a curved sanding block that has been shaped to fit the final curve.

Contrôlez la profondeur au niveau du sillet de chevalet régulièrement ainsi que la symétrie et la régularité de votre travail dans le sens de la longueur et de la largeur ː

Contrôle de la profondeur au niveau du sillet de chevalet.

Contrôle de la régularité du creux en divers endroits.

• Instead of digging the curve, it's possible to add some 3mm thick piece of cork all around.

Note : Florian THOMAS, luthier in Talence (France), gives the folowing advice : add 0.3 mm in the solera's curve. If you planed to obtain a curve with 3mm under the bridge of the guitar, the deepest point on the solera should be dig at 3.3mm.

The neck angle

Roy Courtnall recommends to make the neck angle on the solera.

Notez que la valeur de 3mm pour le renversement du manche est assez élevée et que cela est plutôt d'usage pour les guitares Flamenca. Pour une classique, cette valeur se situe en général plutôt vers 1.5mm. Si vous ne faites pas de renversement, comme dit plus haut, la touche sera alors retravaillée avant le frettage. Notez qu'une combinaison des deux est possible : rabotage de la touche et angle de renversement non nul selon les valeurs choisies. Les valeurs déterminantes sont le galbe de la table d'harmonie,l'angle de renversement du manche et l'épaisseur de la touche (6 à 7mm). Un galbe prononcé implique un angle de renversement moindre et inversement ou un rabotage plus ou moins important de la touche. Pour une première guitare, il est préférable de s'en tenir aux valeurs les plus communes comme par exemple un renversement de 1.5mm et un galbe de 3mm ou bien un renversement nul et un galbe identique avec réduction de l'épaisseur de la touche. L'angle de renversement impose de retravailler le dessous de la touche avant collage sur le manche et la table d'harmonie pour qu'il se conforme parfaitement à l'angle formé par les deux pièces..

• It's not an obligation. We can choose to make a flat neck, with a 0° angle with the body, and then, plane directly the fingerboard in the bass region, next to the rosette (near the last frets).

• Instead of making a gentle slope on the solera's neck, you can also decide to remove 3 mm all along the solera's neck and next, when assembling the body and the neck, use a wedge to adjust the angle. It permits to use different neck angles for different guitars with the same solera.

Plane directly the fingerboard

In this case, glue the fingerboard all along with the same thickness and plane it directly on the guitar. Take care to protect the soundboard with pieces of wood, plywood or cardboard.

For more informations, read the chapter 5 dedicated to the fingerboard.

Roy Courtnall method : a little tip

If you choose to make a neck angle with a value of 3 mm as described by Roy Courtnall.

A wedge is placed on the solera at a specific distance from the end of its "neck" so that the resulting angle allows to reduce the thickness of 3mm at its end and gentle slope to the location of the twelfth fret.

The 12th fret is positioned 320mm from the end of the neck of the solera. So we have 2 points  : A ( 0,0) and B (320, -3) and this equation : y = - 0.009375x. If, for instance, the wedge is 5mm thick, y is replaced by 5 and we have 5 = - 0.009375x. We finally obtain x = -5/0.009675 = -533.33

The wedge should be placed at a distance o 533,33mm from the location of the 12th fret.

• With a big mason's rule, stick a coarse sandpaper (P50)
• Sand with this rule based on the wedge until the sanding marks are as close as possible to the location of the twelfth fret .
• We should obtain a slope to the twelfth fret (point 0) at the end of the neck to the desired angle.

• Another method would be to use a router mounted on two large aluminum rules with the correct angle relative to the neck of the solera.

Moules support d'éclisse

Ces supports ne sont pas obligatoires, de simples équerres en bois placées judicieusement sur le pourtour des éclisses sont suffisantes et permettent de s'adapter à plusieurs formes de guitare.

Si vous choisissez de réaliser ces moules, cet article détaille leur fabrication.