Re; Helper springs WAS Re: Key Leads and Inertia

[David Love]

The problem I find might be solved in the following manner.  Use a helper
spring on the way up attached to the wippen (as usual).  Employ another
spring attached to the hammer flange pressing down on the top of the hammer
shank which would help to reset the hammer and keep it from bouncing around
(one of the problems with assist springs).  By utilizing the wippen assist
for 15 grams, say, and the hammer shank return spring for 5 grams, you
would still enjoy a net benefit of 10 grams off the FW.  Might be a small
clearance problem under the block, but hey, we sent a man to the moon
didn't we?  Or did we? 

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Bill Ballard <yardbird@vermontel.net>
> To: Pianotech <pianotech@ptg.org>; <davidlovepianos@earthlink.net>
> Date: 6/14/2003 8:48:08 PM
> Subject: Re; Helper springs WAS Re: Key Leads and Inertia
>
> At 8:23 AM -0700 6/14/03, David Love wrote:
> >I can't comment from real scientific data, but I have never liked the
feel
> >of assist springs when they are tensioned above some undetermined amount
> >(say, 10 - 15 grams which is typically the level at which they are used),
> >if at all.  I am suspicious of the disconnect that they create between
key
> >and wippen with the assist spring always pushing the wippen away from the
> >key.  Any bounce in the hammer off the rest rail (something that they
also
> >contribute to) will enhance this disconnect.
>
> Figure a hammer weight at #1 of 7.5 to 13.5g, multiplied by~ a 7:1 
> shank ratio would feel like to 95g measured at the knuckle. the 
> uplift of the spring on the the wippen could be measured at the jack 
> (at the knuckle, really), and compared to this (the positive figure 
> with the spring attached, and the negative without the spring).
>
> >My hypothesis is that an
> >assist spring will work best when used in conjunction with a rocker arm
> >capstan arrangement in which the key is directly linked to the wippen.
>
> I would suggest that the helper should be applied to the driven lever 
> (the shank on the way up and the key on the way down) and not an 
> intermediate lever (the wippen in both directions). If the driven 
> lever can be the restrained one, then the chances of it becoming 
> uncoupled from the levers driving it on the return is kept to a 
> minimum. Actually, as the hammer and wippen return to the starting 
> position, the spring is offering its maximum resistance to the 
> hammer's motion, and is in its best position for damping the hammer's 
> return motion.
>
> The coupling issue would seem to come down to that requirement, that 
> the helping (or impeding, on the return trip) be applied to the 
> driven lever. What I'd like to know is, if the helper springs really 
> make the SWs seem smaller, how is the dynamic  behavior of a spring 
> balanced action different from one with  simply, equivalently light 
> hammers. (Obviously I'm not interested in the sound of a hammer which 
> is 10-15g lighter; practically it doesn't exist.) The coupling 
> differences of springs and magnets aside, I believe they would behave 
> similarly, directly and immediately reducing the force of gravity, 
> and to the extent that we removed FWs whose work was now being done 
> by helpers, reducing the force of inertia.
>
> I think that would be worth a couple of oatmeal cookies.
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>
> "No one builds the *perfect* piano, you can only remove the obstacles 
> to that perfection during the building."
>      ...........LaRoy Edwards, Yamaha International Corp
> +++++++++++++++++++++