What's all this I hear about Inertia ?

[Fenton Murray]

>Key lead inertia problems will show up in repetition, where the rep lever 
>spring has to shove the back of the key, lifting the heavy front, for the 
>jack to reset.

That's exactly what it feels like. I think of that heavy hammer on a knuckle 
digging way down into the repetition spring as the key is played. There no 
doubt in my mind that I can feel the lead in the key. I haven't set up a new 
action with assist springs, but I've lightened or removed them and then 
added lead to the key, making the action worse. This on a high ratio, heavy 
hammer, action. Proper procedure for me in this scenario now is to remove 
hammers, lighten them, change knuckle and capstan location as required, and 
start removing lead to achieve a 38 to 40 BW.
Let's say we've got a shank ratio of 8.3 to one and a 9 gram hammer, that's 
74.7 grams that the repetition lever is supporting at the knuckle. Lower the 
hammer to say 8.2 and move the knuckle out 1.5 mm and the shank drops to 
maybe 7.6 and now we've got maybe 68 grams of load at the knuckle. This is 
maybe over simplistic but it works in my head and I play these action after 
I'm done and am getting a real handle on what numbers mean to the feel of 
the action. The dark ages of the '70s and 80's, at least out here on the 
West Coast, are gone and now I'm learning why an action feels like it does. 
It's hammer weight, action ratio, action geometry and friction, then 
finally, accurate regulation. Those first four were missing in my book for a 
long time.
Fenton
----- Original Message ----- 
From: "Ron Nossaman" <rnossaman at cox.net>
To: "Pianotech List" <pianotech at ptg.org>
Sent: Tuesday, September 30, 2008 10:10 AM
Subject: Re: What's all this I hear about Inertia ?


>> If you have heavy hammers, or a high action ratio, or even worse both, 
>> you will start to end up with too much lead in the key unless you are 
>> using assist springs. These actions are not going to 'feel' right even 
>> though they may have great numbers. I don't know any way too measure this 
>> easily with weights at the key board, but I have become pretty good at 
>> feeling it through all the great mistakes I've made.
>> Respectfully,
>> Fenton
>
> And assist springs won't make up for the heavy hammers in the inertia 
> battle.
>
> I've tried to point out before (Not to you, Fenton, to the list), that the 
> excess lead wouldn't be in the keys in the first place unless the hammer 
> weight is too heavy for the action ratio. I don't think key lead has a lot 
> to do with down stroke inertial feel. You'll get a similar feel with less 
> key lead and more spring assist because you're still accelerating a heavy 
> hammer at a nominally 5:1 leverage ratio. The root problem is hammer 
> weight. Key lead inertia problems will show up in repetition, where the 
> rep lever spring has to shove the back of the key, lifting the heavy 
> front, for the jack to reset.
>
> My take,
> Ron N
>
>