MOInertia

[John Hartman]

madelyn mrykalo wrote:
> John,

> Doesnt the leverage system of the action reduce the hammer's effect on 
> moi?  So if you take the moi of the hammer /shank assembly separately 
> (taking it out of the chain of leverages), will it not seem as though it 
> has a greater effect than it really does? 

Vince,

Well no, the MOI of the hammer and shank become magnified by the 
action's leverage. At least that's what the equation for reflected 
inertia would suggest. I made a drawing to show how this works attached 
to an earlier post. It is a little complicated but it makes sense if you 
fallow the logic of the basic principles of physics. Mark D. came up 
with the same thing and so far no one has disputed the equation so for 
now I am assuming it's right.

One thing to keep in mind is that counter balancing with lead in the 
front of the key is a necessary step to make the action function since 
without them soft playing would be very difficult to control. I think of 
the Balance weigh as setting the lowest threshold  for soft playing. If, 
for example, you have a BW of 38grams, the very least force needed to 
start to move the action is 38gm*gravity or 38gm*980cm/sec^2. Balance 
weight doesn't tell us anything about how the action will respond to 
more force than this.

John Hartman RPT

John Hartman Pianos
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Rebuilding Steinway and Mason & Hamlin
Grand Pianos Since 1979

Piano Technicians Journal
Journal Illustrator/Contributing Editor
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