How does it work? - quite well! ....... Watch the video:
More - some techie stuff
The folding of the neck is a natural idea to reduce the size of the guitar - the implementation is the tricky part - and the Eo design overcomes these key challenges::
· geometric alignment of the guitar neck
· robustness.
· keeping nylon strings in tune when the neck is folded.
· Light weight and microphonics / buzz resistant.
The patented joint mechanism is accurately made by CNC (computer numerically controlled) cutting using aerospace type machinery capable of 10's of micron accuracy. It is made in anodised aluminium which means it is light weight but strong and has a durable stain - resistant finish. The parts are dimensioned mainly so that they are strong enough to withstand the forces when manipulating the neck - folding and unfolding. The force on the system when the guitar is in its stable, normal playing configuration, is actually of less concern, the bigger forces can accrue during folding and unfolding, etc.
These are the basic concepts:
String length (assume 650 mm scale)
String tension (assume normal classical strings):
Now if we can fold the neck, and retain the strings about a fixed point in relation to the body, we get this:
And in terms of the folded - up tension - note that if the string length is maintained (31.416 + 309.292 + 309.292= 650mm), the tension is maintained, which means that the tuning will not drift in nylon strings with their complex tension / memory effect. (Guitar strings are tuned by changing their length with the machine winders, which through the stress / strain, Youngs modulus properties, establishes the tension and thereby, frequency of vibration. )
What the Eo concept achieves is to accurately place a mandrel about which the strings are held within a rotating joint, fixed to the body and neck..
The joint mechanism implements a "pinless axis" and this device allows an offset to be applied in positioning of the folded joint which is useful to keep the folded strings as close as possible to the playing tension.
The joint is integrated into the wood of the neck and body parts using positive screw fixing - no glue to soften at high temperatures. The woods used must be strong, dense enough to provide a stable structure and obviously light weight and of good cosmetic appearance - Walnut and Sapele have been used. Other woods, and combinations of wood, including traditional cedar/ ebony are also used.
The joint is very firmly clamped together using an industrial grade lever clamp, capable of >100kg of tension. The geometrical alignment relies on 1) accurate placement into the wooden neck and body and 2) clamping together the flat faces of the joint when the neck is unfolded. The clamp force is determine by the need to keep the integrity of the neck when the whole guitar is being handled / man handled; the force needed to balance off the string tension is actually not that significant in comparison:
When the guitar is unfolded into its playing position, the geometry of the guitar results in a string-to-fret board angle of approximately 0.4 - 0.5 degree; this means that approximately 0.5 kg of vertical force is needed to balance the string tension: assume 44kg total so 44 * tan (0.5degree) is approximately 0.38 kg. So the strength capability in the clamp (100kg) is more than enough to handle this.
