I have not been working on the guitar for a month or so.
Recently I have been thinking about the spanish heel construction; something which I did not particularly favour.
I was thinking more in terms of a mortise and tenon joint fasten on by bolt and nut.
The particular advantage of this method of construction:
1) It allows the neck and body to be work on separately.
Particularly when it comes to installing the fret wire or french polishing the body
2) It allows to adjust the neck angle after assembly. Spanish heel construction there is no way to adjust the neck angle.
That's why a solera is essential in spanish heel construction; it is to built the neck angle into the solera so that the correct neck angle is maintained during assembly.
Romanillos advocate a different method of construction for the Spanish heel.
The neck angle is only fixed at the time when the back is closed.
Instead of 2 narrows slots to grip the sides at the traditional Spanish heel, the slot is widen into a ramp slot.
At the time of the back closing, a wedge is driven into the ramped slot to hold the correct neck angle in place.
This method allows the final neck angle to be adjusted.
Here is a picture of the Romanillos method of construction.
This particular pic is a construction by an amateur luthier RCoates
Neck angle is the angle where the neck of the guitar makes with the plane of the top board of the guitar.
With forward angle, the neck plane is above the top of the top board of the guitar.
This will cause the saddle to be low, which is essential in flamenco guitars.
However, take note the too much forward angle will cause in determining the saddle height.
The saddle need a certain minimum height and the neck angle cannot be below this minimum height or else the the action at 12 fret would be too high for comfort.
Backward angle will cause the saddle to be high.
An example of extreme backward angle is violin family of instruments.
You can see that the cello's bridge/saddle is a few inches tall.
Zero Neck angle:
Forward neck angle: You can see that the saddle height is reduced.
Backward neck angle: You can see that the saddle height is increased.
NB: the effect of neck angle has been exaggerated to illustrate the difference better. Typical neck angle is very minute in terms of 1 or 2 mm differences at the nut.
See the picture of a Andrea Amati cello from Cremona, it clearly shows the effect of an extreme negative neck angle on the bridge.
Neck relief is the amount of curvature built into the fingerboard to allow the string to vibrate without hitting the fingerboard.