More details for keyhead sliders...
![Image](http://www.gunlaug.no/att/div-2011/keyhead-changer-8b.jpg)
...with
full-size drawing on my site.
The slider guide with ball is at one end of the slider, and changer scissors knife edge at the other. Changer scissors take up full string tension.
Changer scissors have fixed height, but slider guide can in theory be set at any height/angle and be given enough adjustment range to fine-tune exact pressure on the guide ball and the screwed-down guide's angle relative to the slider. The minimal friction between ball and slider will make the ball stay and roll free of its end-stoppers once pedals has been operated once, and a tiny (around 0.1 degree) smaller angle at the (black) guide seat than on the (yellow) slider will counteract the tendency of the ball to move towards the changer scissors during operation/playing.
As can be seen I am designing in "loose", almost "rattling", low pressure contact points where 1/100 millimeter mechanical precision, or not, does not make a difference for tuning precision or cause string noise. The idea is that string tension has to be as precise as the strings allow for for neutral and any change, and that there should be no "mechanical hysteresis" tendencies.
Just want to mention that at a certain point "pragmatism" kicks in and says that "enough is enough and more isn't better", and (hopefully) prevent meaningless and costly over-engineering of details. As long as the mechanics is made precise enough to ensure less than 1 cent detuning in itself, my "mechanical precision" goals have been reached, and I believe that comes down to how sharp and precise I can shape those knife edge connections.
For instance: absolute precision and tight fits in the keyhead slider guide system will be more that upset by not being able to align the string "perfectly" on the tuning pegs every time I change strings, resulting in slight variations in sideways pressure since the tuning pegs go horizontal inwards (as on most PSGs). Unless the ball gets worn too non-circular or the inevitable grooves in the slider/guide aluminum surfaces become too uneven, one 3d string width variation in the slider guide system won't make a 0.1 cent difference to overall tuning precision.
Another point - that I have touched on earlier in this thread - is the intentional vertical "rattle" between neck and "backbone" near the bridge-end I will design, build and tune for. It is an important "tone" detail, but it will cause at least 0.25 cent detuning no matter how well it gets tuned.
Thanks for looking in and commenting.