bore distance: was Re: hammer replacement

[David Love]

Hi Newton:

Historically, many of the European makers short-bored their hammers and 
raked the hammer out a degree or two to insure the hammer was perpendicular 
to the string at impact.  I wonder if they didn't do that for a reason.  
Anybody who has mistakenly regulated the repetition spring with the action 
leaning downward onto their lap only to find when they stuck the action back 
in the case that the spring was to tight knows (hopefully) that starting the 
shank at an angle less acute to the string reduces the force required to 
start the hammer moving (read downweight).  By short-boring the hammers, the 
shank can be set a little higher and the touchweight is reduced (according 
to Richard Davenport's experiment) by a few grams per 1/6".  With recent 
talk from David S. about what he calls "breakaway", that is, the change 
(reduction) in resistance as the key progresses through the stroke; by 
starting with the shank in a little higher position, that overall change 
should be reduced.  In practice, you would be able to control ppp playing 
better by not having to start the key with a certain amount of force and 
back off as the resistance diminishes.  The reduced change in resistance 
from beginning to end of keystroke should result in a smoother feeling 
action.  I guess the question is, what do you sacrifice in regulation to get 
that?  And, is the trade off worth it?

In addition, I'm not sure that boring the hammer for future wear is such a 
good idea.  If the action benefits from a certain bore distance, why 
increase that distance resulting in a mechanical disadvantage until such a 
time that you wear the hammer down to a point when you can adjust the blow 
distance to be where you should have been in the first place.

Just a thought.

David Love

>From: Newton Hunt <nhunt@optonline.net>
>Reply-To: pianotech@ptg.org
>To: pianotech@ptg.org
>Subject: Re: bore distance: was Re: hammer replacement
>Date: Fri, 29 Jun 2001 15:27:15 -0400
>
>Hi David,
>
>The shank should be slightly below horizontal when the hammer is resting on
>the string.  By measuring string height and center pin height, subtract the
>shorter from the longer and you have the bore distance when the hammer is
>against the string, optimum, then at about 1/32 inch for future filing.
>When filing initially the hammer will expand to maintain original
>dimensions.
>
>		Newton
>
>David Love wrote:
> >
> > Newton:
> >
> > Another issue is the starting point for the shank.  Boring to the 
>let-off
> > point positions the shank slightly higher and reduces resistance at the
> > beginning of the key stroke effectively reducing the force required to 
>get
> > the key moving.  (I'm sure there's a more technical explanation)
> >
> > David Love
> >
> > >From: Newton Hunt <nhunt@optonline.net>
> > >Reply-To: pianotech@ptg.org
> > >To: pianotech@ptg.org
> > >Subject: Re: bore distance: was Re: hammer replacement
> > >Date: Fri, 29 Jun 2001 09:41:16 -0400
> > >
> > >Hi David,
> > >
> > >Interesting question you raise.
> > >
> > >I always calculate to string height because that is where the engineer
> > >determined the optimum mechanical advantage for the action.
> > >
> > >But...
> > >
> > >If you measure from bore center to strike point then add 1/8" to an
> > >imaginary line, that line represents the optimum regulation height for
> > that
> > >hammer.  No matter whether that point is below or above the actual 
>string
> > >height.  So, taking that in reverse...
> > >
> > >               Newton
> >
> > _________________________________________________________________
> > Get your FREE download of MSN Explorer at http://explorer.msn.com

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com