[pianotech] Sostenuto

[Jon Page]

 >A few other measurements to make before I decide.  Thanks all.

The main reason why I'll move the tray pivot location (lower) is to 
relieve sliding friction on the key end felt. If the underlever has too 
much of a downwards pitch, there is too much friction and probably 
gouging the end felts. If you are relocating the tray pivot, have the 
key lift the underlever to parallel to the key bed. Beyond that and you 
are crushing the corner of the end felt and reintroducing sliding friction.

Many years ago, Chris Brown drew an X -Y axis on a chalkboard to 
illustrate friction while discussing actions. He went on to say that 
movement directly along the axises would have the lowest friction. As 
you delve further away from either axis with the motion of the action 
parts, the friction increases. To apply that to an underlever: parallel 
to the keybed would be along the X axis, or lowest friction (with the 
tip the furthest point from the Y axis; center pin on zero). As you 
lower the end the of the u/l from the X axis, the tip swings downwards 
closer to the Y axis. As lift is applied, the arc has an element of 
forward/outward motion. The steeper the downward angle, the more forward 
sliding motion is induced. So an arc ending on the virtual X axis would 
have the least forwards motion (friction) added to the lift. Lifting 
beyond the X axis (parallel to the keybed) would reintroduce the sliding 
friction as the arc takes a backwards/inwards sweep and mashes the 
corner edge of the felt to boot, counterproductive all around.

I have eased many actions simply by reducing the u/l sliding friction. I 
posted my latest exploit sometime last year where I removed the support 
blocks and redrilled the holes lower. Not only did it relieve the 
sliding friction but it timed the damper lift with the key better since 
they were lifting way too early. Since the u/l's were suspended by the 
damper wires, lowering the pivot raise the fronts. I didn't have to 
remove the dampers, only tweak a few set screws.

-- 
Regards,

Jon Page