Scruffing -was - Over-Strike vs Under-Strike

[ed440 at mindspring.com]

What does scruffing do to the sound? 
If the hammer did not scruff, would the piano sound different?
How hard do you have to play to have significant scruffing in a vertical?
Is it more significant in a particular range?
Ed Sutton

-----Original Message-----
>From: Frank Emerson <pianoguru at earthlink.net>
>Sent: Nov 25, 2006 1:00 AM
>To: Pianotech List <pianotech at ptg.org>
>Subject: Re: Scruffing -was - Over-Strike vs Under-Strike
>
>It's been a while since I have seen the slow-motion photographic study, but to the best of my recollection, the shank flexing due to impact with the strings seems to overpower other considerations.  Uprights could certainly benefit from more substantial shanks.  I said that my drawing was exaggerated, but not by much.  It is amazing how an upright hammer flops around before coming to rest.  
>
>Frank Emerson
>pianoguru at earthlink.net
>
>
>----- Original Message ----- 
>From: Steve Fujan 
>To: Pianotech List
>Sent: 11/25/2006 12:02:22 AM 
>Subject: Re: Scruffing -was - Over-Strike vs Under-Strike
>
>
>Wow Frank, great sketch!  
>
>Hmm......
>So, if the shank flex causes upward scruff, and the offset axis causes downward scruff, then could they be "tuned' to cancel each other out?
>
>Intuitively, it seems like scruffing and flex are both power and clarity robbers.  Could super stiff shanks help minimize both? 
>
>Steve Fujan
>
>
>
>
>On 11/24/06, Frank Emerson < pianoguru at earthlink.net> wrote:
>How can scruffing occur unless the hammer shank flexes?  It does flex, and it does scruff, but always upward.  As the flagpoling of the shank reverses, the hammer begins to scruff downward just as it is rebounding from the string.  The proximity of the axis of rotation to the string is less significant than the length of the hammer bore from the strike point.    This can be seen in slow-motion photograph of action movement.  It is amazing how much an upright shank flexes.  You would think it would break before flexing as much as it actually does.  A grand shank flexes also, but not nearly so much.  The drawing below is simplistic and exaggerated, but illustrates the point. 
>Frank Emerson
>pianoguru at earthlink.net
>
>
>----- Original Message ----- 
>From: Steve Fujan 
>To: joegarrett at earthlink.net;Pianotech List
>Sent: 11/24/2006 12:47:45 PM 
>Subject: Re: Over-Strike vs Under-Strike 
>
>
>Shifting slightly to the concept of scruffing...    The hammer contact will always "scruff" towards the hammer pivot axis (unless the pivot axis could somehow lie in the plane of the string).   The closer the pivot axis is to the string, the less "scruffing" will occur. 
>Steve Fujan 
>
>
>On 11/24/06, Joseph Garrett < joegarrett at earthlink.net> wrote: 
>Upon reading the follow-ups of Jons query, I'd like to wonder which is
>which. I've always considered "Over-Strike" as the Downward angle of the 
>hammer, which would put the hammer Beyond Perpendicular. ??? Am I correct 
>on that? If so, then, "Under-Strike" would be, where the hammer does not
>achieve Perpendicular, on contact?? The "Over-Strike" hammer, (on an 
>Upright), would "scruff", (for lack of a better word), downward, at impact. 
>The "Under-Stike" hammer would therefore "scruff" upwards.
>Do I have all of this backwards? Confused minds need to know what the 
>consensus is.<G>
>
>
>Joseph Garrett, R.P.T.
>Captain, Tool Police 
>Squares R I