Get the Lead out

[Doug Richards]

Rob,
The inertia IS dependent on the distance from the pivot, 
BUT...

A friend of my did some calculations and measurements on the "total" inertia
of the key/wippen/shank/hammer system.  Because of the mechanical advantage
of the key, it has the least effect on the inertial loading you would feel
when pressing the key.  The hammer mass has the most.  Just try adding some
of the hammer shank weights to your test piano and compare the difference
you feel with the key weight experiment you already did.  I think you will
find that although you can adjust things to that the upweight and downweight
end up "in the zone", the feel will be dramatically different.

doug richards
San Jose, CA

> -----Original Message-----
> From:	Rob Kiddell [SMTP:atonal@telusplanet.net]
> Sent:	Tuesday, October 06, 1998 7:29 PM
> To:	pianotech@ptg.org
> Subject:	Get the Lead out
> 
> Here's a question: 
> 
> 	Recently, I published  an article on grand piano action  diagnosis,
> and one of the conclusions I came to was re-balancing  keys with many 1/2"
> leads per key. Basically I remove larger leads  near the balance rail and
> insert smaller leads near the end of the  key. This seems to make the
> actions feel inertially lighter, and  there is less 'thumping' from heavy
> keys on balance rails.  
> 
> 	However, it was brought to my attention that (I quote here) 
> 
> 
> "When the key is moving the "moment" of inertia becomes much more
> important. Unfortunately it is affected by the distance from the balance
> rail by a factor of R squared. This means a lead weight 2 cm from the rail
> might have a moment of inertia of 1, but that if the weight is 4 cm from
> the  rail the moment of inertia will be 4, 6 cm = 9 and 8 cm = 16!"
> 
> 
> This all makes sense.  However, when I played the piano with 5  1/2" leads
> per key, it felt heavy to play, despite the 55 downweight  30 upweight
> average. With lead removed from near the balance rail  and 3/8" lead
> inserted farther away to balance the key to original  weigh-off, the
> action wasn't as hard on my forearms to play for long  periods.
> 
> 
> Mathematically, it seems that the smaller leads further from the  balance
> rail would result in the same inertia as the larger leads, but  my arms
> don't get tired playing! 
> 
> 
> Any ideas? 
> 
> 
> 
> Rob Kiddell, 
> Registered Piano Technician, PTG
> atonal@telusplanet.net
> 
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> I am the blue screen of death
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> 
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