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Baldwin SF10 Bridge Pin Spacing

  • 1.  Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 02:16
      |   view attached

    So why do you think Baldwin decided to alter the bridge pin spacing in just this small section (that's the tenor/treble break)?

          
       
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    David Love RPT
    www.davidlovepianos.com 
    davidlovepianos@comcast.net
    415 407 8320
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  • 2.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 02:36
    My uneducated guess would be that the extra mm of speaking length for those notes made them sound a little clearer. ???

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    Willem "Wim" Blees, RPT
    Mililani, HI 96789
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  • 3.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 02:58
    I don't think there's any extra speaking length.  The differences seems to be purely in the spacing between the pin rows.  

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 4.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 07:33
    So that the spacing of the front and back pins is not too close to the increase in speaking length per unison. This avoids the higher unisons's back pin intersecting with the next lower unison's front pins.  I do this for the same reason, maintaining my offset angle as I move the pins closer together or farther apart.

    Jim Ialeggio

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
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  • 5.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 11:01
    I do that too but that change is often subtle an only enough to avoid the intersection  This radical and abrupt a change and only in this one section isn't explained by that.  

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 6.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 12:31
    Look at the dogleg at the break. What dogleg? Lacking sufficient dogleg,
    the choices are:

    (1) Compromise the speaking length progression.
    (2) Adjust the pin row spacing.

    Yamaha compromises the speaking length in the P22, hence that F above
    the break tuning nonsense (low break%). Baldwin chose to change the row
    spacing to keep the back row of pins on the bridge. This doesn't hurt a
    thing, and is better than screwing up the speaking lengths. It's hard
    though, to accurately establish the offset angle with the pin rows that
    close. That's on the treble side of the break. On the bass side, it
    looks to me like avoidance of the pins of the next unison. Unlike Yamaha
    and Baldwin (and a lot of others), I choose to build bridges with
    sufficient dogleg at the break to accommodate both the speaking length
    progression and the row spacing. It costs more in time, which likely had
    something to do with their decisions. I still have to adjust row spacing
    as necessary to avoid intersecting the next unison's pins. Yamaha,
    incidentally, maintained the row spacing and moved the whole unison in
    some models.
    Ron N




  • 7.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 14:11
      |   view attached
    If the attachment works, here's an example.
    Ron N




  • 8.  RE:Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 15:32

    I don't quite understand. There's plenty of room behind the speaking length row to maintain the same row spacing through the section. In this case the back row has been moved closer to the front row for no apparent reason.
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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 9.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 16:34
    David L., all,

    My observations (fwiw):
    Four sets of bridge pins to the left of the strut, and four sets of bridge pins to the right of the strut are definitely closer together.

    However, if one looks closer, you'll find the four sets of bridge pins to the left of the strut actually are not equal in location on the bridge. They graduate toward the center of the bridge in the direction of the strut, whereas, the four set of bridge pins to the right of the strut do not duplicate that pattern of graduation in either direction.

    Keith McGavern, RPT
    Shawnee, Oklahoma, USA



  • 10.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 16:53
    In an off list discussion with Del Fandrich the reasoning may have been in order to keep each unison array more centered on the bridge. As both Del and Ron pointed out, it's the lack of dogleg that is at the source of the problem and means that the array will gravitate either toward the back or the front of the bridge (on either side of the strut).  The changing of the front to back spacing, therefore, was to keep the unison centered on the bridge. The correct fix, as was pointed out, would be to make the dogleg adequate to begin with to conform with the speaking lengths.

    In this particular case however, both sides of the strut have adequate room to spread the rows to some more normal distance and, in fact, the treble side of the strut would favor the back of the bridge and the tenor side the front creating, presumably, some type of equilibrium.  So why complicate the offset angle by putting them so close.  I imagine that this may have not been that carefully thought out but rather a factory on-the-fly adjustment of sorts.  

    I do see many pianos where the pattern moves well toward the back (or front) in some sections or others where there seems to be little attempt to actually center the unisons at all, front to back, on the bridge.  So how critical is this centering  Obviously one could go too far with things being off center and thereby apply excess pressure to one side or the other perhaps creating unwanted stresses on the board. But since making slight modifications to existing scales to put them in more consistent logarithmic form is something I do on a fairly regular basis, I'm curious to know at what point this becomes a problem.  



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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 11.  RE:Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 17:06
    The yellow line is where I would contour the bridge, and yes, there's
    plenty of room. That's the intent. Look at the original bridge line.
    That last one on the bass side would be very close to the edge without
    the narrow row spacing. The next three down would interfere with
    adjacent pins like Jim said, so they are narrow too.
    Ron N




  • 12.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 18:30
    Nicely drawn (what did you use to modify that photo with btw).  

    I understand what you're getting at but their solution seems extreme to me.  There's plenty of room to keep the back row away from the edge, avoid the adjacent pins and still maintain a more generous spacing.  I would not have put the rows nearly that close even with that bridge and those speaking lengths--certainly not on the unisons that are farther away from the strut on both sides. Perhaps the choice is somewhat random without real reasoning.

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 13.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 18:40
      |   view attached
    Here, for example, is a picture of a new treble bridge cap on a Steinway B treble in which I've created a log scale through each section. You'll notice especially in the lower capo section at the strut the speaking line drifts back quite a ways toward the middle of the bridge yet the spacing graduates down smoothly without problems of interference.   I saw no particular reason to jump to 6 mm spacing four notes up from the strut.  

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 14.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 18:46
    > Nicely drawn (what did you use to modify that photo with btw).

    Corel Draw,


    > I understand what you're getting at but their solution seems extreme
    > to me. There's plenty of room to keep the back row away from the
    > edge, avoid the adjacent pins and still maintain a more generous
    > spacing. I would not have put the rows nearly that close even with
    > that bridge and those speaking lengths--certainly not on the unisons
    > that are farther away from the strut on both sides. Perhaps the
    > choice is somewhat random without real reasoning.

    Extreme, maybe, but I outlined my opinion as to why they did it. What
    their real reasoning was in all detail, I can't say. Had they just built
    the bridge with adequate dogleg in the first place, it wouldn't have
    come up at all.

    Ron N




  • 15.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 12-19-2014 19:07
    In the big picture, there is, as we can all attest to, often a discrepancy between design intent and as built conditions.

    The bridge  and speaking lengths are designed and drawn out, the shape of the bridge committed, then the laminations coming out of the press and drying springs a little. In a bridge sweep, a little spring can result in some serious as built corrections in the heat of battle.

    Then the plate and board has to go in exactly at design locations, all indexed off the case which iften has its own tolerance issues on the factory floor.

    I think its reasonable that some of what we see is defined by design intent, and much of what we see is as built work-arounds. Add to this, that we as small rebuilders can take the time to work this kind of work-around out in a way that a factory workman can't, as the time allowed for the task is limited.

    I think all of the factors we have all mentioned are in play in this kind of thing, which leaves design intent and reasoning somewhat...flexible, in the heat of battle.

    The big point for me is, that I don't think what they did makes a bit of difference tonally, from any of my own work...so they just made it work.

     

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
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  • 16.  RE: Baldwin SF10 Bridge Pin Spacing

    Registered Piano Technician
    Posted 12-19-2014 19:32
    No I don't think so either.  My own preference is not to get the pin rows that close and create unnecessary pressure on the cap should the dogleg turn out to be a bit more severe than one intended.  So unless there's a compelling reason I would try to avoid rows that close.  To reiterate what Ron (and Del) said, with an adequate dogleg there's not a problem or need for a work around.  Of course if you are working with an existing bridgeroot attached to a soundboard then it's more difficult to address.    

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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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    ...snip

    The big point for me is, that I don't think what they did makes a bit of difference tonally, from any of my own work...so they just made it work.

     

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
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  • 17.  RE: Baldwin SF10 Bridge Pin Spacing

    Posted 02-20-2015 22:33
    When I look at that picture, I see a deliberate attempt to change how the 4 notes--on either side of the bar--render during tuning. Because of the closer bridge pin spacing, the increased side-bearing will tend to 'trap' more of the tension at the backside of the scaling.

    With prolonged exposure of the plate to an extreme temperature (e.g, overnight on a truck), these are the exact number of notes that create a temporary bell-shaped curve in the tuning (i.e., which is different, and in addition to, the temperature change to the string itself). I could easily understand how a piano builder might want to see if this type of change to the bridge system might prevent the plate from unevenly interacting with the tuning.

    Just another theory...