MOInertia

[John Hartman]

Richard Brekne wrote:

> I've asked this point on two occasions already and we havn't gotten
> really into the point. Its one thing to point out the individual MOI of
> the parts as John, and others have done. But how these turn out after
> leverage is figured would be another thing. If it came anywhere close to
> the roughly 5:1 ratio figure... then suddenly the Hammer and Shank MOI
> become reduced by a factor of 5 and we are talking a whole different
> degree of significance for the key MOI.

  Richard,

I thought I sent a drawing with how the leverage effects the MOI of the 
parts in the action chain? If you didn't see this I can send it to you 
off-list. The leverage that effects the MOI is different than the 
leverage that effects static balance. With MOI the angles that the wip 
and shank go through in relation to the angle the key travels is what is 
used.

[link redacted at request of site owner - Jul 25, 2015]
>>
>>   
>>     Key MOI = 10,307 gmcm^2
>>     Wippen MOI = 3149 gmcm*2
>>     Hammer and shank MOI = 165,528 gmcm*2

These figures are adjusted for the reflected MOI in relation to the key. 
If you add these all together they are the MOI of the action. The total 
MOI controls how the action responds to a force applied to the front end 
of the key. In particular how much acceleration the front end of the key 
   will achieve in relation to a given force.  In a loose sense the MOI 
is to action dynamics what balance weight is to static balance.

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]