Lost motion: (was puzzler on M & H BB

[Porritt, David]

Ed:

If your blocked wippen did show some hammer movement when the jack was
tripped out that would indicate that the jack was indeed holding the
knuckle with no lost motion and the hammer dropped down to the
repetition lever when the jack moved away.

dp

David M. Porritt
dporritt at smu.edu

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On
Behalf Of A440A at aol.com
Sent: Monday, September 25, 2006 9:16 PM
To: pianotech at ptg.org
Subject: Re: Lost motion: (was puzzler on M & H BB

Conrad  writes:

<<  I agree with the method of setting the wink,('tis how I do it)
however I 

> have to disagree with the conclusion that there is no lost motion.

      Small point here, but I never said anything about a wink.  I said
that 
I want to feel the jack in contact with the knuckle.  I often feel the 
leather/jack friction without seeing a movement.  




> 

> I believe that the scraping is felt as the _edge_ or corner of the
jack 

> rubs as it leave from under the knuckle. As it stands at rest, with
the 

> jacktop surface tangent to the knuckle curve, that there is a very
small 

> amount of a gap. That little gap (paper thin?) amounts to lost motion 

> and is there for the same reason as that in an upright - to allow the 

> jack to reset for the next stroke. >>

     I don't know about this.  I also don't know how one would measure
it.  
However, I can't assume that the knuckle and jack are not in contact by
the 
theoretical geometry of the jack's arc, ie. given the resilience of the
leather, 
if the distal edge of the jack is aligned with the distal edge of the 
knuckle's core, the  arc of the jack's leading edge will easily compress
the  small 
amount of leather that would interfere with the sweep of the jack as it
is moved 
out from under the knuckle.  
     There is no need to guess at this, though.  simply block the
whippen so 
that it cannot move, and regulate the balancier so that the jack can
just be 
felt moving across the leather.  I find that I can do this and not see
any 
dropping of the hammer, which suggests that there is no lost motion
between the 
two.  
Regards, 

Ed Foote RPT 
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html