Inertia

[John Hartman]

madelyn mrykalo wrote:
> 
> I would like to address the notion that changing
> moment of inertia of the key is not really going to
> accomplish much because the hammer is what really
> affects m.o.i..  For some reason, the key does have a
> noticeable effect.  Let me give an example. 

Vince,

I am not sure what your customer is relating to but the evidence seams 
to be that adding leads to the keys does not raise the total MOI of the 
action very much. This is because the increase in angular motion from 
the key to the hammer increases the Moi of the hammer much more than 
than than the 5/1 leverage we usual think about.

I figured the MOI for the three action parts of a typical note. The 
hammer was 8 gms and there were three leads in the key. The front arm of 
the key was 25cm and action leverage was 5.3/1 with a BW of 35gms. Here 
are the number for the MOI as adjusted for reflected MOI:

Key MOI = 10,307 gmcm^2
Wippen MOI = 3149 gmcm*2
Hammer and shank MOI = 165,528 gmcm*2

There may be many virtues for keeping leads out of the keys but I can't 
see how it makes very much difference to the perceived weight of the 
action. The difference in MOI due to the leads you mentioned seam 
insignificant to the total picture.

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]