Action Geometry

[robert goodale]

Yesterday I worked on a new Chinese grand.  This was easily the
biggest piece of @&%#%*!!  I have ever seen.  There were so many
things wrong I don't know where to begin. Among some of the more
obvious, key leveling was merely a "suggestion", and the thin key
pins, (almost describable as "wires"), were all in different
positions, some so far back that they weren't making contact with
the bushing felt at all.  The felt in general was of the cheapest
quality I have ever seen.  The damper wires were a joke, each one
with it's own unique bend.  The under levers were the type with
both the bendable spoon and the leveling capstan on the bottom.
As a result no effort was made whatsoever to maintain some degree
of leveling when the wires were installed.  Instead, the spoons
and capstans were bent in a variety of extreme positions to make
them lift in a somewhat uniform order.  The key frame looked like
it was cut from scrap material from a factory that made something
else.

The complaint was that there were sticking keys and noises.  What
I found was that the drop tab on the wippen was rubbing against
the hammer flange rail.  Seems that the wippen rail is the type
with the oval shaped screw holes where the screws fastens onto
the brackets.  The rail was set too far forward, causing the
wippens to rub against the hammer rail.  Actually the screws were
so loose that the rail just decided be were it wanted.  The best
I can figure is that it never was tight from the beginning, and
it was just "regulated", (ha ha), in the position it happened to
be in.  It's position was so extreme that even with the jack
capstan screws in their most extreme position they would not
align correctly with the knuckle.

After analyzing the problem, I moved the rail in what I
determined to be the correct position.  The result was that the
hammers moved upward above the back rail considerably, greatly
reducing blow distance.  I proceeded to properly align the jacks,
lower the hammers to proper blow distance, and then set the let
off, (the hammers where now blocking after resetting the jacks).
At this point there was insufficient dip so that let off on most
of the keys was barely possible only when pressing them down
hard.  I proceeded to take the stack off and and add to the
balance rail to increase dip, (there were not enough front rail
punchings to remove to establish proper dip).  While I was at it,
I regulated the key pins so that they were centered in the
bushings.  Success! The action felt horrible, (Which I think is
mostly attributed to it's design- probably done on the back of a
dinner napkin), but it did function.  I checked the springs and
drop, did a quick string/hammer alignment, and left it go at
that.

I think under the circumstances I did a pretty good job.  Action
geometry, however, is a subject that I have never fully
understood enough to feel truly confident in.  Perhaps we can
start a thread on this, (action spread distance, wippen
dimensions, hammer shank length, tail length, back check height,
etc.).  whatcha think?

Rob Goodale, RPT