Sohmer Agraffe Bridges

[A440A@aol.com]

Greetings, 
  So far:
 Jim wrote:
 >  Than there are the bridge agraffe thingees, like Ed's little Sohmer
>  > grand which actually have 'upbearing'
>  >in a portion of the scale and 'downbearing' in another portion of th 
scale(JB)
>
>  Not quite.  As Ed Foote described it: (DAVID)
>
>  Yes "quite" without regard to how Ed described it. Any downbearing on the
>back of the agraffed bridge is a function of the upbearing on the agraffe and
>not downbearing as we know and use the term. Ever seen a busted agraffe 
>down by
>the tuning web...Those little suckers just pop right on up there don't they?
>Wellllllll that is what also happens on an agraffed bridge when one of them
>break.
>Could it do that if in fact there were any true downbearing present?
>> Does  anyone have a good picture of an agraffe bridge that could be 
posted to resolve this, soon to turn violent, debate?  Lacking such a 
photo, anyone with a relevant model in front of them who would venture an 
opinion?  As I am remembering, the net effect of this config was to put a 
major ripple in the soundboard under the bridge.  <<

   Violent?  With a "Cupid Model" grand piano??  Hell yea,  we techs are a 
psychotic lot, no?  Or was that supposed to read "Violet" as in the color of 
love.... 
 
    Actually,  I took my Lowell bearing gauge and eyeballs to this piano, 
measured the bearing, and examined the board.  It is difficult to really tell 
what the ripple effect (not to be confused with feelings of omnipotence that 
follow drinking three bottles of Ripple), on this board might be, since there is a 
maple plate that runs the full length of the bridge on the bottom of the 
soundboard, which makes normal crown determination somewhat of a problem.  The 
ribs are notched over this plate,(more on that later). 
    The downbearing is not totally unconventional, but bears (dang right 
that's a pun) mentioning.  
    The top octave, which has no agraffes on the bridge, has a LOT of 
deflection in the normal sense.  With the tool leveled on the speaking length, the 
bridge measures higher in front, and the strings certainly angle their way down 
to the duplex bar in front of the hitch pins.  It looks a little excessive but 
the top octave on this little piano really screams.  Maybe it is worth 
mentioning that the C8 string length is 2.20 inches!  (Do I hear the scalers 
starting to scream, too?)

    Assume all measurements with the Lowell gauge begin with leveling it on 
the speaking length, and all deviations are in contrast to this baseline.   At 
C6 the string definitely rises from the back of the agraffe to the 
back(distal) side of the bridge, so the agraffe would pop up if the threads broke.  
However, from the back edge of the bridge to the hitch pin, there is a downward 
angle to the string, so I read this as indicating that the total bearing pressure 
at this string is downward. The same holds true for the next octave or so.  
  At C5, I notice that the downward angle in the backstring has approached 
zero, yet there is still a certain amount of rise from the back of the agraffe 
to the distal edge of the bridge.  This may be an area where the bearing is 
actually trying to lift the soundboard.  Or it may result in a zero pressure 
either way.  Hard to tell. 
   Below C4, the bearing once again returns to normal cumulative downward 
pressure, with the aforementioned rise from agraffe to distal edge of bridge.   
The bass, which has no agraffes, exhibits a large amount of downbearing. 
  My feeling is that the agraffes were an acoustical endeavor and that the 
board originally had coventional downbearing throughout. The one section near C5 
where the the backstring and speaking length were at the same angle, 
interrupted by the small rise from agraffe to bridge, is where I normally see boards 
flatten out with age.  
   Now, about those cut-out bridges.  In the area of zero deflection (C5),  I 
notice that there is a small break in the glue joint between the notch in the 
rib and that long continuous maple plate.  This break is wider at the front, 
making it appear that the bridge has attempted to roll back,(distally).   For 
this to happen,  I believe that the downbearing had to have been lost and the 
bridge was slightly rolled backwards in this section.  This is also the most 
tonally deficient area of the piano, which, without a doubt, is either simply 
coincidental or irrefutable proof that bridge roll kills sustain.  Take your 
pick.  
Regards, 
 
Ed Foote RPT 
http://www.uk-piano.org/edfoote/index.html
www.uk-piano.org/edfoote/well_tempered_piano.html