Keyleads and MOI

[John Hartman]

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]