[pianotech] Sostenuto

[David Love]

Helpful.  Thank Jon.

David Love
www.davidlovepianos.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Jon Page
Sent: Sunday, February 17, 2013 8:00 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Sostenuto

 >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