Keyleads and MOI

[Richard Brekne]

John... and Ed

First Ed... the answer to your question is most certainly dependent on
your views as to what's good enough in the first place. Very many will
have it that even Stanwoods method is overkill. Jim Ellis points out
that as long as you have fairly even set of hammers (weight wise) and
are careful and meticulous in installing them and doing the weigh off,
you will end up with a fine playing instrument. Factories have used
traditional weigh off for years thus, and we all know the good ones do
good work, where as others leave some to be desired. I would point out
that, from scratch, a Stanwood job takes about the same amount of time,
and allows a degree of latitude for action configuration that
traditional weigh off does not readily lend itself to. But whatever. In
the end you have to do a fine job in an amount of time you can make
money with. Beyond that its up to you to go as far as you will, for
whatever market you can find that will appreciate your efforts.

Ed

We keep going apparently back and forth on this Key leading issue. I
know what you have had to say remains consistent. But I find seeming
conflict between on the one hand stating that moving key leads around
can only account for 1% (an insignificant amount) of the total MOI, and
then on the other hand acknowledge there can be a problem with key too
much key inertia to begin with. I know the two are somewhat unrelated...
but not THAT distantly. If you can actually cause a noticeable change in
action behavior by installing too much key MOI, then its hard to accept
that smaller changes are can not be felt without further ado. What would
be the percent difference between a key with the maximum amount of key
leads under any circumstances you could accept, and a key with none ? At
what point does this difference become insignificant.

I dunno... seems to me that a key with 40 grams of lead distributed
around the midpoint between the balance rail pin and the key front is
simply bound to feel significantly different then the same key with 20
grams of lead at the key front. 

Perhaps I am having difficulty with your definition of "dynamic
response". I would think that would include things that influence
repetition, but you seem to separate the two below.

John Hartman wrote:
> 
> Ed Sutton wrote:
> 
> > Throughout this discussion I have been trying to find an answer to the
> > question "How can I tell if it matters enough to do something about it?"
> > and "Is there a point of diminishing return where we should stop
> > worrying about key lead placement?"  As practicing piano
> > technicians, this is the question we are all seeking to answer.
> >
> 
> Ed,
> A while back I posted some numbers on the MOI of the key, wip and
> ham/shank. Looking at these numbers it would seem the key is the largest
> contributor to the action's MOI. But when you figure the reflected MOI
> of the hammer and shank the situation looks quite different. The hammer
> and shank contribute most of the MOI felt at the key. This shows that
> worrying about lead placement and the MOI of the key is just a waist of
> time. At least in relation to dynamic response of the action. It may
> still be useful to limit the MOI of the key to improve repetition.
> 
> Approximate MOI:
> 
> Key = .002 kgm^2
> Wip =  .000085 kgm^2
> Ham/shank = .00016 kgm^2
> 
> MOI reflected to key:
> 
> Key = .002 kgm^2
> wip = .000315 kgm^2
> Ham/shank = .01655 kgm^2
> 
> The Moi of the key is only about 10% of the total MOI so moving leads
> around will change the total action MOI by about 1% at best. That's a
> lot of work for a small improvement.
> 
> John Hartman RPT
> 
> John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
> Rebuilding Steinway and Mason & Hamlin
> Grand Pianos Since 1979
> 
> Piano Technicians Journal
> Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]
> 
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